Audio
So you’ve got a camera and you are ready to make some terrific videos. That’s great, but one of the biggest mistakes that beginning videographers make is that they forget the importance of audio. Whether you are shooting news, a corporate video, or a dramatic scene for an entertainment show, nothing undermines the quality of your production faster than bad audio. The sound that accompanies your video has to be clear, clean, and appropriate for the video that you are shooting. This means that attention must be paid to sound and how you collect it. This chapter takes you through the basics of what you need to know about collecting sound for your video and the importance of understanding microphones.
Microphones (mics) are the first link in the technical chain that forms an audio production. The choice, placement, and quality of the microphone help determine how strong this link will be. Capturing good audio is essential to video projects; therefore, it is important to understand how microphones work.
Microphones have existed for more than 135 years. The first was used in Alexander Graham Bell’s telephone to change audible sound waves into electrical energy. It was a simple and inexpensive carbon microphone sensitive to the pressure of the sound waves typically generated by the human voice.
MICROPHONE STRUCTURE
A microphone is a transducer, a device that changes energy from one form to another. Microphones change sound or acoustical energy into electrical energy, or more specifically, sound waves into electrical signals. Sound waves strike the microphone’s diaphragm and the microphone’s element translates that physical energy into electrical energy. The diaphragm is the part of the microphone that moves when it is struck by sound waves. The element, which is connected to the diaphragm, is the part inside the microphone that translates this physical movement into an electrical signal.
Four basic designs have been used for microphone elements over the years: carbon, ceramic, dynamic, and condenser. The first two, carbon and ceramic, were used in early mics, but they are rarely used in professional audio work now. The latter two, dynamic and condenser, are the microphones of choice for almost all professionals. Because each element has unique electrical and sonic properties, knowing the differences between them will help you choose the right mic for the job.
MICROPHONES AND AUDIO-RECORDING TECHNIQUES
Dynamic Microphones
Dynamic microphones have parts inside them that physically move when struck by sound waves. This movement creates an electrical current, which duplicates the sound wave and becomes the audio signal. Although various companies have manufactured many different variations of dynamic elements, there are two general classifications: the moving-coil type and the ribbon, or velocity, type.
Moving-Coil Microphones
Most moving-coil microphones are made up of a Mylar diaphragm attached to a coil of wire called a voice coil, which is suspended within a magnetic field. As the term dynamic implies, dynamic elements are designed to allow movement. A moving-coil element consists of a finely wound coil of wire suspended in a magnetic field. When the diaphragm is struck by sound waves, the coil moves within the magnetic field. The movement within the magnetic field induces voltage fluctuations in the coil, which becomes the output signal.
Moving-coil microphones are the most widely used in professional audio applications for several reasons:
• They have a very good frequency response, similar to what our ears hear, and can gather audio from many different kinds of sources. A common frequency range for a professional dynamic mic is 40 to 15,000 Hz.
• Generally they are the most ruggedly designed mics available: they are shock resistant, unimpaired by most temperature extremes, insensitive to extremes in humidity, and can withstand high sound pressure levels without overloading.
• They do not require an external power source (known as phantom power, +48 volts).
• They are generally inexpensive.
Ribbon, or Velocity, Microphones
Another dynamic microphone similar to the moving-coil mic is the ribbon (or velocity) mic, in which a thin ribbon-like piece of corrugated metal is positioned between the poles of a magnet. When struck by sound waves, the ribbon vibrates between the magnetic poles, causing a small voltage in the ribbon that becomes the electronic audio signal. Because the ribbon is flat, it is sensitive to sound wave pressure striking it directly from either the front or the back. Ribbon mics were used extensively in the 1930s and 1940s in studio-produced radio. Although they are very sensitive and have a very good high-frequency response, their drawbacks include shock sensitivity, fragility, and noncompact size. Ribbon microphones are rarely used in professional video production, but recording engineers find them useful under certain circumstances for their unique frequency response.
Condenser Elements
Condenser microphones have a thin diaphragm that serves as one plate of a capacitor. Capable of storing electrical charges, a capacitor is an electrical component with two electrodes, two plates of metal (+ and −), separated by a small distance. Unlike the dynamic element, which makes use of electromagnetism to generate an electrical signal, condenser mics operate on a principle known as variable capacitance. The diaphragm and the backplate act as the electrodes of a capacitor.
When sound waves strike the diaphragm, the distance between the two electrodes changes, producing a change in the capacitance of the element. This results in a very small voltage signal that becomes the electronic audio signal.
The quality of a condenser mic depends on the design of its capsule, which is the condenser element and its acoustic system or housing. The capsule plays a major role in how the mic responds, not only to different frequencies but also to different directions of sounds.
A condenser microphone requires two additional features to produce its audio signal. One is an impedance-converting amplifier that converts the signal to low impedance to enhance signal quality. The other feature is a power supply. DC power is required to charge the capacitor element or, more specifically, to polarize the two plates of the capacitor and provide power for the amplifier circuit inside the microphone.
FIGURE 9.1
Diagrams of (A) dynamic and (B) condenser microphones. (Courtesy of Shure Brothers, Inc.)
In an electret condenser microphone, a more recent condenser microphone design, the voltage needs of the mic are smaller. The diaphragm is made of a dielectric material that is capable of permanently holding a charge. The power supply is needed only for the preamplifier. A good electret condenser mic should hold its internal charge for 10 years or more, but will eventually wear out. A disadvantage of this type of microphone is its inability to respond to the higher frequencies.
The power that a condenser microphone requires to operate is commonly called phantom power, or +48 volts. It is referred to as phantom power because the power is supplied to the microphone along the same wire that carries the audio signal. Recording consoles, field mixers, and high-quality ENG/EFP cameras are capable of supplying phantom power. However, this is not the only way condensers can be powered. Many condenser microphones are equipped with space for a battery inside the mic that will supply the power for the element and amplifier, or an external box can be inserted on the microphone cable that produces +48 volts along the mic cable. Very high-quality recording microphones come with a specific power supply for the microphone, providing the utmost efficiency for the microphone’s design and performance.
Considered the mic of choice for accurate sound recording in professional work, condenser microphones are very sensitive and have excellent frequency response. One drawback is that they are more expensive than their dynamic counterparts; a second is that they require a power supply. A battery does not at first seem like a serious drawback, but when you are in the field, providing power to a mic can become a problem if you are not prepared. Finally, condenser microphones are sometimes too sensitive for extremely noisy situations or sudden loud noises, and are sometimes inappropriate for outdoor use.
SENSITIVITY
Microphones are also categorized by their sensitivity—their ability to reproduce sound in several different ways. A microphone’s sensitivity to sound is its ability to hear quiet sounds, or its ability to produce a relatively high voltage level at its output. A microphone’s directional sensitivity is how well a microphone hears from different directions, and its frequency response is a measurement of the mic’s ability to pick up sounds of differing pitch or wavelengths.
Sound Sensitivity
Microphone sensitivity is defined as the amount of electrical signal a microphone produces from a given input sound source. Different mics have different sensitivities; some mics simply put out a stronger signal than others. Sensitivity is determined by measuring the microphone’s electrical output when the mic is placed by a sound source of a known intensity or pressure. At first it may seem that the more sensitive a mic is, the better; however, experienced audio production practitioners realize that good audio production consists of the absence of sounds you do not want to hear as well as the presence of sounds you do want to hear. Overly sensitive mics can be just as much a problem as those that are insensitive.
FIGURE 9.2
This lavaliere mic has a detachable power supply, allowing it to be used with a wireless transmitter.
Directional Sensitivity
Microphones have different abilities to pick up sound from varying directions. A polar response chart (Figure 9.3) is a representation of the pickup pattern, or polar pattern, of a particular mic. The mic’s polar pattern determines where sounds can originate and still be transduced into an electric signal. Manufacturers usually provide polar response charts to provide technically accurate information about the pickup characteristics of individual microphones so that the end user can understand the directional characteristic of the microphone and place it accordingly in practical use. These standardized charts depict the angle of sound sensitivity relative to the element of the microphone and sound pressure levels. In effect, they show how a mic will respond to sounds that come from various angles and at various levels of sound pressure. The head of the mic is at the center of the chart. Sounds coming from the top, or 0 degrees, are called on axis and those from the side, or 90 degrees, off axis.
A microphone’s ability to gather sounds at various degrees off axis is what determines how directional the mic is. Generally, as the distance from the mic is increased, the sound picked up by the mic is decreased. On the chart, this is shown by the concentric circles around the tip of a microphone, which represent sound levels that decrease in intensity as you go away from the mic. The concentric circles closer to the mic tip will have a higher level of decibels or dB. Mics with different pickup patterns will pick up sounds that come from different directions. An omnidirectional mic picks up sound equally from all directions, but a unidirectional mic like a cardiod will pick up sounds primarily from the area in front of the mic.
These charts are especially helpful because there are many variations of the general pickup patterns. Also, many mics have slightly different patterns at different frequencies. In addition, there are some hybrid and altered versions of the standard patterns. Three major polar patterns describe professional mics: omnidirectional, unidirectional, and bidirectional.
Omnidirectional
Omnidirectional mics are capable of picking up sound equally from all directions. The omnidirectional pickup pattern can be imagined as a three-dimensional sphere with the microphone’s diaphragm in the center. If you place an omnidirectional mic in the center of a circle of people, the sound level coming from any of those people should be almost identical to the others, assuming that they are all equidistant from the mic and all persons are speaking at about the same level. The mic’s diaphragm can react to sound pressure changes equally from all directions. However, an omnidirectional mic does tend to be more directional at higher sound frequencies; it is best to point the mic in the direction of the primary sound source to be recorded. In other words, even for an omnidirectional mic, sound on axis will tend to be of better quality than sounds off axis.
FIGURE 9.3
Polar response charts for various microphone types. The shaded areas show where sounds can be picked up by the microphone.
Unidirectional
Unidirectional mics are capable of picking up sound from only one direction. The unidirectional pattern can be imagined as a heart-shaped sphere originating at the microphone’s diaphragm. Unidirectional mics use a pressure-gradient device and/or reflectors to achieve this directional characteristic. These mics can respond to differences in audio pressure between the two faces of its diaphragm (the pressure-gradient device), or they can achieve directionality by the use of a reflector. Some designs use a combination of these methods. Directional mics are good at reducing background noise from two sources: (1) off-axis sounds and (2) excessive reverberation (usually found inside small rooms). They can also be placed at a greater distance from the sound source while maintaining their frequency response and sensitivity. These are the mics of choice in stereo recording because of their ability to give a sense of sound location.
Cardioid/Supercardioid/Hypercardioid When pressure-gradient and reflector designs are combined in one mic, the resulting pattern is called a cardioid. Cardioid microphones are unidirectional and pick up sound primarily from one direction. The word cardioid comes from the shape of its response chart, an inverted heart-shaped pattern. Cardioid microphones pick up sounds almost entirely from the area directly in front of the mic and almost nothing from the far sides or rear, which makes them very desirable in noisy situations. The three basic patterns are cardioid, supercardioid, and hypercardioid.
Each pattern has the same characteristic of rejecting sounds from behind and to the sides of the microphone, yet there are some imperfections. As the polar pattern is narrowed to achieve more directionality in front of the microphone (supercardioid and hypercardioid), the mic’s sensitivity to sounds directly behind it increases. This is the trade-off for being able to focus on only the sound directly in front of the microphone, and is generally not a problem.
FIGURE 9.4
An Electro-Voice® RE-10 dynamic supercardioid microphone. The ribbed shaft aids in the directionality of the microphone.
Ultradirectional More directional than the hypercardioid, the ultradirectional or shotgun microphone uses an entirely different capsule design to achieve its special purpose. The shotgun mic allows even greater distance between mic and source and greater rejection of off-axis sounds. The design is simply a tube with the diaphragm at one end. The tube has slits in it covered by an audio-dampening material to ensure the full frequency response of the on-axis sounds. This allows sound to enter the tube from straight on (parallel to the tube or on axis), while reflecting off-axis sound through the slits. In general, the longer the tube, the more directional the shotgun mic is, and the further away the sound source can be. Because its polar pattern is more sensitive to a wide range of frequencies, it is more directional for higher frequencies than for lower ones.
The shotgun is the workhorse microphone of ENG and EFP work. For the standalone newsperson, a shotgun mounted on the camera is the primary source of natural sound and sometimes even interview sound. A two-person news crew uses the shotgun for almost all sound gathering. In EFP production, the shotgun is often boom-mounted for precise sound gathering in the studio and on location where hidden mics are not possible. When using a shotgun microphone, it is critical that the user wear headphones that monitor the microphone’s signal, since a small error in aiming, or placing, an ultradirectional microphone can produce a big change in audio quality.
Bidirectional
A bidirectional microphone picks up sound equally from only two directions. Resembling a figure eight, its pickup pattern is achieved in mics that are purely pressure-gradient devices (no reflectors used). The most common of these mics is the ribbon mic. One of the oldest mic designs around, the ribbon mic is still widely used today in radio and studio work. If you interview someone who is at the same but opposite distance as you are from the mic and who speaks at about the same volume, a bidirectional mic will be equally sensitive to both voices and eliminate any side audio. This assumes that your locations are at the correct angles relative to the mic.
FREQUENCY RESPONSE
The goal of a sound technician is to accurately capture the sound source for reproduction. This requires a microphone capable of picking up the entire frequency spectrum of the sound waves that strike the mic’s transducing element. A mic used for picking up conversation needs to be sensitive to the frequencies of the human voice, a range of about 100 to 10,000 Hz. A mic used in a sound studio for picking up the sounds of a piccolo must accurately transduce frequencies as low as 500 Hz and as high as 15,000 Hz. Although the construction and pickup pattern of a mic may qualify it for a particular application, it should not be used unless it has the appropriate frequency response capabilities.
Most professional-quality microphones can reproduce sounds within a frequency range of about 500 to 15,000 Hz. A chart like Figure 9.5 can show a mic’s frequency response or sensitivity to various frequencies of sound.
FIGURE 9.5
Frequency response chart for a dynamic microphone. (Courtesy of Shure Brothers, Inc.)
Ideally, the microphone will have a flat response curve, which implies that the mic is equally sensitive to all frequencies in its range, but this is rarely the case. The most common weakness in mic frequency response appears at the upper end of its frequency range, where the response curve drops off considerably, demonstrating an inability to reproduce sound waves at high frequencies. This dropoff is present at low frequencies, but is not quite as common and often less important. Many mics are designed with special characteristics to slightly alter their frequency response.
It is common to have a mic with a bass rolloff switch of some sort, allowing the user to purposefully deemphasize frequencies at the low end of the audio spectrum. This helps correct the proximity effect, or the tendency of unidirectional and bidirectional mics to emphasize the bass or low-frequency response when the sound source is close to the mic. Bass rolloff can also be useful to eliminate troublesome environmental noise like air conditioners, footsteps that can shake a mic stand, clothes rustle, or the rumble of a distant train. (See Figure 9.6.) Other mics used in vocal work sometimes have a presence boost in the upper midrange to enhance the voice. These features also help add brilliance, clarity, and general intelligibility to the sounds recorded.
IMPEDANCE
Microphones can also be differentiated by several technical factors. One factor, impedance, is very important, because selecting the wrong impedance mic can cause immediate and sometimes serious problems. Other factors, like output noise and maximum sound pressure, are important only in very specific situations when the production requires specific sound pickup other than typical voice or music, or in situations with a lot of interfering signals or sounds.
Microphone Impedance
Microphone impedance refers to the amount of resistance a signal encounters in a microphone circuit. The more impedance in a circuit, the less signal will flow out of it. Therefore, all other things being equal, low-impedance microphones are more efficient in signal flow and therefore produce more signal than high-impedance microphones.
Most professional mics have low impedance, which allows long audio cable runs without significant loss of signal. Their higher level of signal, relative to high-impedance mics, gives better rejection of hum and other types of interference. Also, low-impedance mics are compatible with almost all professional audio and video equipment.
Although impedance levels are rated as high or low (corresponding to the designations high Z or low Z), mics can be found that are somewhere in between. Table 9.1 lists typical microphone impedance levels and their corresponding measurement in ohms, the unit of electrical resistance.
The impedance of most professional mics is usually 150 ohms; it is measured as −60 dB, which is referred to as mic level. After an audio signal has been passed through a mixer, recorder, microwave transmitter, or any other processing device, the signal coming from that device is usually sent at a medium impedance of 600 ohms and is measured as 4 dB, which is referred to as line level. When audio signals are called high or low in professional situations, that usually means the line level is high (more signal) and the mic level is low (less signal). In other words, a mic level signal is weak and a line level signal is strong. For a mic level signal to reach line level, it must be amplified, which occurs when the low-impedance signal is processed by a mic preamplifier.
FIGURE 9.6
The bass rolloff switch is located below the ribs, near the bottom of the shaft of this mic.
TABLE 9.1 Typical Microphone Impedance Levels and Their Corresponding Measurements
| Rating in Ohms | Impedance Level |
| 38 to 150 | Low |
| 600 to 2,400 | Medium |
| 9,600 and above | High |
Overload
When mics are bombarded with more audio signal than they can process accurately, the mic is overloaded. Dynamic mics are very hard to overload. They have very low distortion across their entire 140-dB dynamic range. The same cannot be said for condenser mics. At high acoustic levels, the output signal of the capsule can overload the impedance converter circuit in the microphone. Some mics have built-in pads (an inline device that can change the signal that passes through it) that can reduce the signal level, sometimes at the cost of adding noise to the sound, thus reducing quality.
The sound recordist must also be cautious not to overload the microphone preamplifier that boosts the electrical signal for recording. If a grating or distorted sound is heard that is not an accurate reproduction of your sound source, it must be determined which link in the chain is overloading. It could be caused by the microphone or the mic preamplifier, or by a problem with the mic cable.
OTHER FACTORS
Besides the major considerations of element construction, pickup pattern, frequency range, sensitivity, and impedance, several other factors should be considered when selecting a microphone. Hum and radio frequency interference, signal-to-noise ratio, output noise, clipping level, and maximum sound pressure are often specified by the manufacturer. Some of these factors are critical for broadcast applications, but are not as important in other applications.
SELECTION AND PLACEMENT
Now that the numerous characteristics of microphones have been explained, it is appropriate to discuss how to use this information to complete the processes of mic selection and mic placement.
Choosing a Mic
Mics have varying elements, pickup patterns, frequency responses, impedances, appearances, applications, and special accessories, such as built-in filters. In addition, some mics even have a personality—a sound different from other similarly constructed or designed microphones. Because of the variety of choices, it seems that the selection process could be lengthy and complicated. Fortunately, this is not usually the case. Most audio production facilities have a finite selection of mics available for production work. This selection consists of representatives of the different types of mics available: omnidirectional, unidirectional, dynamic, condenser, and so on. Not many production houses would stay in business if they decided to buy an additional microphone whenever the producer or production manager decided that a different mic might be somewhat better than those already owned. High-quality microphones are expensive. Good-quality microphones can often yield high-quality sound in a variety of situations, and many good mics often overlap each other in what they can do well. For example, a cardioid mic is best for many interview situations, but an omnidirectional mic might work just as well if you can keep the extraneous noise in the room low and keep the omnidirectional mic close to the source.
FIGURE 9.7
Various shapes and sizes of handheld mics.
Four factors should be considered when selecting the best mic for a production:
• What are the general production goals: What is the end product supposed to be, how will it be distributed, who will the audience be, and what quality level should be obtained?
• What is the sound source that is being captured? Is it a voice, a specific musical instrument or group of instruments, or environmental sounds? How loud is the source and what frequencies is it producing?
• How much control will there be over the sound environment?
• How many sound sources are involved in the production?
• Will the mic be on camera? If so, what are the aesthetics of the mic?
Placing a Mic
When placing a microphone it is critical to understand the mic’s polar pickup pattern—its directionality. The sound recordist must point the microphone in the proper direction and also place the microphone in the proper proximity to the sound source so that the mic can produce a useable electrical signal. The microphone’s sensitivity characteristics should be seriously considered when placing a mic. An understanding of a mic’s sensitivity, polar pattern, and frequency response affect where the recordist will place a particular microphone in relation to the sound source.
Not only must you choose a mic based on its design characteristics but also based on where the mic must or can be placed. Limitations such as personnel, budget, time, boom shadows, and environmental concerns can dictate which mics you can use and where they can be placed. Knowing how to place a particular mic helps you to identify whether a particular mic is right for the job and can make the difference in capturing usable or unusable audio.
STYLE
Of all the equipment manufactured for the reproduction of sound, microphones display the widest range of appearance and design. Although there are many different brands of audio recorders, they vary only slightly in appearance. Microphones can range in size from a lavaliere, sometimes smaller than a dime, to a shotgun mic more than two feet long, to a studio overhead mic the size of a large grapefruit. Because microphones vary extensively in size, weight, appearance, and application, knowledge of these factors provides a better understanding of how to use microphones and select the one appropriate to the task.
Handheld Microphones
The handheld mic category is the broadest of the style categories. It is not a question of which mics are in it but which ones are not. A typical handheld mic found throughout the world today is the Electro-Voice 635A.
This omnidirectional dynamic mic is so rugged it could be used as a hammer. Built to last a lifetime, it is the generic and general-purpose mic. The mic is small enough to fit in a hand and light enough not to be a strain. Most handheld mics are similar to the 635A in appearance. They have a relatively small head or capsule for the diaphragm at the end of a four- or five-inch shaft. Handheld mics can have any polar pattern, can be either dynamic or condenser, and can have various quality levels. Another example of this type of mic is the Shure SM58.
A handheld mic is generally used by a singer or someone addressing the camera or interviewing a subject. Because it is easily manipulated, it is good for gathering sound quickly from multiple sources, such as when a reporter doing an interview points the mic at the person talking with little effort or even walks the mic closer to the source. Almost all handheld mics are made with a pleasing appearance so that they will not be distracting on camera. Handheld mics can be mounted on a desk or floor mic stand. In ENG work, where speed can be the overriding factor in getting the job done, the handheld mic is indispensable because of its versatility despite any limitations. However, the disadvantages are limited pickup range and sound quality that is not always optimal.
FIGURE 9.8
Two rugged mics used on location: A. The Electro-Voice 635A and B. The Shure SM 58.
Mounted Microphones
Mounted mics can be one of two types, studio or shotgun mics, and are designed to be supported by a mechanical system such as a desk stand or overhead boom.
Studio mics are designed for the highest quality sound reproduction. Because appearance is not important, these mics may be larger than those that appear on camera or on a speaker’s podium. The on-camera or podium mics are sometimes referred to as desk mics, but are still designed for studio use only. Studio mics are not moved often, especially not when sound is being recorded. Many have solid or integral mic-attachment devices or specialized shock mounts that reduce low frequencies traveling into the microphone from the stand. These specialized mounts must be used on mic booms and floor stands.
Shotgun mics are generally not meant to be handheld. You can mount a shotgun mic in any of three primary ways: (1) on a camera, (2) on a studio boom or stand, or (3) on a portable boom called a fishpole.
Both studio and shotgun mics require a fair degree of isolation from mechanical noise, that is, noise caused by handling or brushing up against something. A good camera mount for a shotgun has a rubber pad in the holder surrounding the mic to cushion it from shock. A boom usually has a suspension system of heavy-duty rubber bands (a shock mount), so that the shotgun literally floats within the holding bracket.
FIGURE 9.9
This microphone is mounted on a fishpole that can extend to a long length, which helps to get the mic close to the sound source while staying out of the shot.
Generally, shotgun mics are not meant to be seen by the camera, so their appearance does not matter. They can gather quality audio at a distance from the sound source. Because they are so directional, a boom allows the operator to position the mics at the best possible angle to get only the desired sound while keeping the mics out of the shot.
The disadvantage of mounted mics is their need to be fixed to a certain location. The most widely used mic system in professional video production, the fishpole shotgun, is fixed to the fishpole and requires a full-time operator. If the shotgun is fixed to a camera, it cannot always be at the right angle to cut out unwanted background noise or to capture the sound source desired; it will gather any and all sounds in front of it.
FIGURE 9.10
A typical lav with windscreen and attaching devices.
Lavaliere Microphones
Lavaliere or mini-microphones became quite popular when TV presented new problems for audio production professionals. The mics used on TV had to sound good, and they also had to have an acceptable appearance on camera. The lavaliere mic was an answer to this appearance problem. Designed to be worn by the person whose voice is to be recorded, lavaliere mics (also called lavs or lapel mics) are quite small and unobtrusive. Lavs are usually condenser microphones, although there are some dynamic lavs. All condenser lavs need a power source to work, but dynamic lavs do not.
The microphone head or capsule is at the end of a long, thin cable run from the power unit. Most lavs use standard AA batteries but they can also be powered by the camera or mixer using phantom power. The end of the power unit acts as the connector end of the mic with the standard male XLR receptacle. Lavaliere mics are almost always constructed with an omnidirectional pickup pattern, because the sound of the human voice emanates from the mouth in an omnidirectional pattern as the head turns during speaking. Designed to be worn either against the clothing of the person or beneath an article of clothing, such as a tie, scarf, or shirt, lavaliere mics are designed with a built-in boost in the high-frequency range because the sound reaching the mic may be filtered by the cloth and cause higher frequencies to be missed. For live TV, two of these mics are often placed on the same tie clip in a technique known as dual redundancy to provide a backup if one fails.
SPECIAL APPLICATIONS
In addition to the considerations of structure, sensitivity, impedance, and style, the type of application for the mic may influence which mic is best for your audio needs. Special application microphones have been developed to meet the needs of some atypical applications.
Performance Microphones
Microphones designed for performances will usually have special characteristics or devices built into them to suit the needs of audio performers. Consider the needs of a performer like Beyonce. Because of her bouncing, swinging, and jolting style of singing, she needs a mic that will take some abuse. First, her mic should have a shock mounting that dampens the noise created from rough handling. She would also need a mic that would withstand the explosive wind and breath sounds generated from her movement and her style of singing. Mics designed for this purpose have a special filter called a pop or blast filter that will stabilize the diaphragm, thereby minimizing the distortion and allowing truer sound reproduction. Performance mics are often used at very close range. Anyone who has seen rock stars perform on TV knows that they practically swallow the mic as they sing. Mics used for this purpose must have the characteristics that enhance the singer’s vocal qualities, sometimes including a bass rolloff feature to minimize a booming low-frequency sound or a boost of the upper midrange frequencies. Another common design feature of performance mics is the ability to reject background noise to permit a higher amplification level for the desired sound before getting audio feedback in the system. For artists who prefer holding their microphones, lightweight mics are a necessity.
FIGURE 9.11
(A) Headset mics like those used by sportscasters. (B) This small and lightweight mic fits under and around the ear. Because it is almost invisible, it is more appropriate for on-camera use.
Multiple-Application Microphones
Some microphones are now designed and marketed to be used in a wide variety of applications. These mics are designed so that they are able to provide different pickup patterns in different situations. The mics designed in this way are also known as convertible or system mics. These mics often come with several attachments that allow different configurations for various applications. Some mics change configuration by the flip of a switch. Essentially, this type of mic can function as an omnidirectional or unidirectional mic, or even one or more variations of the special cardioid patterns to provide the pickup abilities of various types of shotgun mics. As with any multipurpose tool, this type of mic may not be as good in any one configuration as the best mic of that type. However, this slight trade-off of some sound quality excellence for versatility is a worthwhile one for many users with limited budgets but a wide range of audio pickup needs.
Headset Microphones
Headset microphones are mounted on a bracket with one or two earphones attached. This headset is worn on the head of announcers in both radio and TV. Their use in TV can be seen most often in sporting event announcing and network reporters on the floor of the political conventions.
The headset mic has a mini-boom that holds the mic in place very close to the announcer’s mouth. This is especially important in situations where the announcer has no hands free, but may have to turn his head to follow action or receive information from another person. This mic can have either a dynamic or condenser element. Its pickup pattern is cardioid, because the important sounds are coming from one source, the announcer’s mouth. A popular variation of this mic is the microheadset mic. This type of mic has also become very popular with on-stage singers, especially those who incorporate lots of movement into their acts.
Surface-Mount and Pressure-Zone Microphones
Surface-mount and pressure-zone microphones, also called boundary mics, are usually used in situations where two or more people are the source for audio to be recorded or broadcast, and these people are positioned in front of a flat surface such as the floor or a table.
These microphones are commonly seen on either side of a politician on the clear plastic rectangles that appear on camera. These rectangles are teleprompters that display the text of the politician’s speech but cannot be seen by the audience. In most cases there is a main microphone in front of the speaker and the microphones on the rectangles are used for redundancy and sound support for the main microphone and/or to add room tone.
The polar pickup patterns of these mics are somewhat different than conventional mics. The mics come with both omni- and unidirectional patterns, but only one hemisphere of the omnidirectional sphere or unidirectional heart shape is available.
When this type of mic is unidirectional, it can be used to isolate a particular vocalist or part of a musical group. It can also function as a single instrument mic, for example, for a bass drum, by placing the mic on the floor directly in front of the instrument.
You can create your own boundary mic with mics you already have. By taking a handheld mic or lav and laying it parallel to the floor or any boundary surface, pointing it to the center of the sound source, and raising it just slightly (1 or 2 mm) off that surface with a bit of tape or something else small, you can achieve a close approximation of an actual boundary mic.
FIGURE 9.12
Two examples of pressure-zone microphones.
Wireless Microphones
In many production situations, a standard microphone with a cable is not appropriate. Cables are not attractive on camera and can cause the talent to fall. Sometimes, production personnel or others at the location can trip on an audio cable, causing injury or pulling the cable out of the equipment it is connected to. The wireless microphone, often referred to as a radio-frequency (RF) mic, frees the person being mic’ed from the tether of an audio cable, which is often aesthetically undesirable or downright impractical in film or TV shots.
The belt pack radio transmitter, used for lavaliere microphones, is attached to the person being mic’ed. A plug is attached directly to the mic or other audio source and sends the radio signal encoded with the audio information to a receiver. The standard receiving distance is usually no more than 100 feet, but with a very good system the receiver may be at a location up to one-quarter mile away. Some handheld microphones have the transmitter built into the mic shaft itself.
Although wireless mics are essential in location TV work, they should be treated with caution. A great many factors can arise to interfere with the signal. This is particularly true in urban environments, where various electrical sources and other RF signals from standard broadcasting and point-to-point communications generate radio-frequency interference.
FIGURE 9.13
A wireless microphone system can consist of any standard mic connected to a small portable radio transmitter.
RF mics come in two frequency ranges: VHF (very high frequency) and UHF (ultra high frequency). Years ago, VHF frequencies (174 to 216 MHz) were very popular because they worked fairly well and were cheap to buy. But they were also very susceptible to interference of all kinds. Toward the end of the 1990s, the entire radio frequency spectrum was reshuffled by the FCC to accommodate digital TV and a host of new users. Most frequencies common before 1990 are no longer available today. Some older RF mics are not legal under the current FCC rules for frequency use. For that reason, most wireless mics sold now are in the UHF frequency range (450 Mhz and above). They provide much better range and reliability than earlier systems, but they do cost more. When you buy a professional wireless mic, you will be asked where the mic will be used to help ensure that you will not be using a frequency that many others in the same market will also be using. A mic bought in Phoenix for use in that market may not work well in Los Angeles. Production crews traveling around the country often carry wireless systems that can change frequencies to adapt to the local airwaves. These wireless mics are called frequency agile. Even with these, if more than one set of wireless mics are being used, the soundperson must take care to make sure the frequencies are spread out from one another to avoid interference. A large production or a network news crew may use up to eight wireless mics at one time. Keeping them all clear can be a headache, especially when traveling.
One of the biggest causes of interference is reflected radio waves from the transmitter striking the receiver at different times, just like reflected audio waves cause echo. The path between transmitter and receiver must be as clear of obstructions as possible, especially anything made of metal. To further improve your chances of getting a good signal, make sure the receiving and transmitting antennas are parallel; in other words, one cannot be horizontal while the other is vertical. Also, be sure that the antennas are not curled or bunched up if they are the soft type.
One type of wireless that cures some of the interference problems is the diversity system. In effect, in this system each transmitter has two receivers. The system switches seamlessly to whichever receiver has the best signal so there is no interruption of the sound.
Getting the signal into the typical wireless belt pack transmitter (the type most commonly used) is not as easy as it might look. Each brand of transmitter has its own special cable connector for its associated microphone, and it is not usually compatible with anything else. You will need an adapter cable that goes from a female XLR to the particular transmitter’s connector type to attach a different microphone to it. Because most wireless situations call for the use of a lav mic, it is beneficial to have one wired to plug directly into the transmitter. Some transmitters, called plug-ons, can be plugged directly into an audio line or the bottom of a mic. They are more bulky and cannot be hidden on a person as easily as the belt pack can.
FIGURE 9.14
A typical wireless transmitter, receiver, and mics.
FIGURE 9.15
An Electro-Voice RE50/B mic shown with a mic clasp to attach it to a mic stand. The mic is designed to reduce wind and popping noise and features an internal shock mount to reduce handling noise.
ACCESSORIES
Differing applications and locations demand that microphones be flexible enough to be positioned in various places under numerous conditions. Many accessories are available to the audio technician for mounting the mic and ensuring that quality sound can be gathered under adverse conditions.
Mounts
Microphones are not freestanding instruments and require a device or mounting system to keep them secured in place. For interviewing or sound collection on location, this is most often accomplished by simply holding the mic in hand. Most mics are shipped with a mic clip. The mic clip allows the mic to be attached to a microphone stand. Many mics will fit in a standard mic clip. But many mics have very customized designs and the mic clip that is supplied by the manufacturer is a must have if you are going to use the microphone. Mics with smaller shafts need their special mic clip, and highly sensitive recording mics and shotguns must use their custom shock mounting devices so that they may be attached to a mic stand.
FIGURE 9.16
(A) A zeppelin system is used for cutting down wind noise. (B) Various windscreens. The windscreen at the right would fit a shotgun mic; the small windscreen below fits a lavaliere mic.
Acoustic Filters and Windscreens
Some microphones are designed to cope with problems inherent in close mic’ing. Inexperienced announcers and people who are being interviewed may pop their Ps, (speak too loudly or forcefully), or blast the microphone with too much sound. Many mics now have pop-and-blast filters built into them to correct these problems. These filters are contained inside the mic housing; the sound must pass through them before striking the diaphragm. Some pop filters are designed for use in front of the mic rather than inside it. These filters are called pop screens, and are made of a mesh material. They are positioned between the speaker/singer and the mic, and are common in recording studios and radio stations.
Windscreens are foam-rubber-like casings designed to fit over the top of a microphone. Almost all hand mics, lavalieres, and headset microphones can be used with windscreens to reduce the sound made by air currents or wind. The effectiveness of this type of windscreen can vary greatly depending on the nature of the mic. In general, the more directional a mic is, the more susceptible it is to wind noise, and the harder it is to protect. Because shotgun mics are the most affected by wind, a simple foam windscreen is not enough to achieve quality audio under windy conditions. For optimum sound, a shotgun is used in a basket-type windscreen called a zeppelin. This device surrounds the mic with a space of dead air while allowing most audible frequencies to pass through. (See Figure 9.16.)
AUDIO CABLES AND CONNECTORS
To complete the technical chain of an audio system, the signal must get to a recording device through an electrical interface: a cable and its connectors.
Balanced and Unbalanced Lines
An unbalanced line is the type of audio line found in most consumer-level audio products and camcorders. The cable consists of a single conductor carrying the positive signal and a shield carrying the negative signal of a circuit. While this type of line is fine for most consumer needs, it is limited to cable lengths of less than 10 feet to maintain quality and can be susceptible to outside electrical interference, especially in cable lengths of more than 10 feet. This type of line is not recommended for any professional use. Unbalanced lines often have to be used on camcorders that have a mini-plug external mic input.
In a balanced audio line, the mic signal is carried by two leads instead of one. The shield is the ground so that the conductor leads are completely isolated from other electrical components. A balanced line is far less susceptible to RF interference and ground loop hum found in unbalanced lines. If you must connect a balanced line to an unbalanced line, it is best to have a one-to-one isolation transformer between the two. This device keeps the ground loop of the unbalanced line from inducing hum or noise in the balanced line.
FIGURE 9.17
Audio-balanced line (XLR) connectors. On the left is a male connector; on the right is a female connector.
Connectors and Adapters
The standard connector for balanced audio lines is the three-contact XLR type, sometimes referred to as a cannon connector. The input end of an XLR cable is always a female connector (receptacles for the connector pins), and the output end is always a male connector (the connector pins). A microphone always has a male connector. The XLR connectors are the only type used in professional audio recording but may not be the only types encountered in field production or news gathering.
It is typical in ENG work to be asked to record audio sources from a wide variety of systems in the field. A good audio kit should include adapters to tap into any of these systems.
The most common is the ¼-inch phono plug. This plug comes in balanced (stereo) and unbalanced (mono) versions. In most cases, you will not need a stereo signal. This ¼-inch connector is the most common way to tap into a house public address (PA) system or audio mixing board not designed for video production. The output of such systems is usually labeled “monitor out” and is typically mono at mic level, but it can be line level or even a nonstandard level. Many video supply companies sell adapters that are ¼-inch phone (stereo or mono) at one end and XLR at the other.
Other connectors that you are likely to encounter in the field are the ⅛-inch or mini-plug, the RCA-type connector that your stereo uses. While adapters are available to convert these plugs to XLR, it is quite easy to make up short cables with the different types of connectors at each input end and an XLR at the other.
FIGURE 9.18
Three popular unbalanced audio connectors: from left to right, ¼-inch phono plug, RCA type, and ⅛-inch mini-plug.
Signal Loss in Audio Cable
A mic level signal is able to travel up to 200 feet or more with insignificant loss of signal strength. On very long runs, a loss of some audio frequencies may occur as well as an increased susceptibility to hum or electrical interference. For long distances, it may be necessary to amplify the audio with a mixer near the source end to deliver enough signal strength to the cable destination. By amplifying the signal to line level from mic level, a higher-quality signal with less hum can be transferred over a greater distance.
Phase
If the polarity of the audio cables or mics used in a single system does not match, the signal may be out of phase and cause the cancellation of some frequencies or the entire signal itself. This can be a very tricky problem to track down without the use of a volt-ohm meter or a cable tester. While this problem is not common, it is possible. If you find a cable or source that is out of phase, a small in-line adapter can reverse the phase (polarity) of the audio line, or you can rewire the cable or connector.
Filters and Pads
A variety of in-line filters and pads in barrel style are available that aid the audio-gathering process. These items can be invaluable in getting the most out of your mics and overcoming weak points in your audio system. One common style is a barrel shape, which allows you to put the filter or pad in the audio line at any point where there is a connection.
• Switchable Attenuator Pad. A switchable attenuator pad reduces impedance by 15, 20, or 25 dB to avoid overload distortion at the recorder from too strong a signal. It also comes in handy for matching audio signal strengths.
• Line Adapter. A line adapter is a 50-dB attenuator that reduces line level to mic level. Whereas the output level of many mixers, VCRs, recorders, and amplifiers is at line level, many recorders and most wireless transmitters accept only mic level input.
• High-Pass Filter. A high-pass filter reduces bass and rumble by rolling off or cutting out the low frequencies. It allows high frequencies to pass through the circuit and reduces the low frequencies. This filter is good for reducing air conditioner noise and wind rumble.
• Low-Pass Filter. A low-pass filter reduces hiss by rolling off or cutting out the high frequencies. It allows the low frequencies to pass through the circuit and reduces the high frequencies.
• Presence Adapter. A presence adapter gives a slight boost in the upper midrange of frequencies to enhance the quality of the human voice.
• Response Shaper. A response shaper puts a slight dip in the upper midrange of frequencies to reduce the sibilance that can sometimes be present in certain mics or mic’ing situations.
FIGURE 9.19
Three-to-one rule: if Mic 1 is one foot in front of speaker 1, Mic 2 should be three feet from Mic 1.
Handheld Microphones
A handheld mic is often the easiest to use. You simply pick it up and point it at the source of the sound. Singers, TV evangelists, used-car salespersons, and TV reporters often use handheld mics, which are made for gathering audio close to the source. Meant to be seen on camera most of the time, handheld mics do not require a boom person or as much time and hassle to put in place as a hidden lavaliere would require. There is just one hard-and-fast rule: They must be within about one to two feet of the source of audio. Some handheld mics are shock-mounted within their outer shell to withstand rough handling without creating excessive mechanical noise. The Electro-Voice RE-50 is an internal shock-mounted mic well suited for ENG work.
A news photographer working without a soundperson may have no choice but to give the reporter a handheld mic to gather almost all the audio, especially for interviews and stand-ups. The handheld mic allows the reporter to place the mic where it can get the best sound. If the news crew is talking to a gathering of steel workers outside a closed factory, the reporter can maneuver the mic to whichever person is talking while being able to bring the mic back to record the questions as well. This approach can be problematic, because without a shock-mounted mic, the sound of fidgeting fingers on the mic can be very distracting.
In EFP work the handheld mic is used more often as a prop and not out of necessity, as in ENG. Because the quality of the audio is more important in EFP, it is not a good idea to leave the handling and placement of the mic in the hands of the talent. That is why most EFP crews have a soundperson. Some talent, such as a used-car salesperson, likes to have a mic to hold onto like a security blanket. It may in fact be just a prop, with the actual sound being recorded by an unseen mic. If you have time, budget, or personnel, there are usually better ways to get that audio in many situations. The best exception to this rule is in the case of singers, but even they are now using the newer micro-headset mics to free their hands for instrument playing or dancing.
Even when a handheld mic is used on a floor or desk stand, it still must be within two feet of the sound source to obtain good-quality sound. As the mic is placed further from the sound source, the risk of the audio sounding hollow or having an echo is increased. For a news conference at which several speakers are seated at a long table, using more than one mic is a good alternative. It is best to follow the three-to-one rule in the placement of the mics, however many people are present. This principle says that for every unit of distance between the mic and the audio source, the distance between mics should be at least three times greater. The greater the directionality of the mic, the less chance of phase problems from reflected sounds or multiple mics. (See Figure 9.19)
FIGURE 9.20
A front and back view of how to properly attach a lav mic to clothing using an alligator clip. It not only properly positions the cable, but also helps dampen cable noise.
Camera-Mounted Microphones
The best mic to mount on a camera is the ultradirectional type, although any type of mic can be used. A shotgun microphone will pick up audio mostly from the camera’s field of vision. Sounds that come from the sides (outside of the picture) are not picked up nearly as well. Even in highly directional mics, there are still flanges (off-axis lobes) of sound pickup to the side and rear areas of the mic. Although those flanges are not as sensitive as the on-axis lobes of the polar response chart, they may still pick up some unwanted sounds, such as the reporter whispering in your ear next to the side of the mic while you are shooting.
Sound gathered at the camera is usually referred to as background (BG) audio. Most producers refer to it as natural sound (natsound), or the sound the camera naturally hears. It is the most valuable sound an ENG person can get. Natural sound is what makes many pictures come alive. Having it can mean the difference in keeping your job or losing it. Some news photographers try to use their camera mic to do reporterless interviews. Under certain time pressures or acoustic conditions this may be acceptable, but most of the time it is not. The photographer places the camera (and therefore the mic) as close to the subject as possible to reduce the amount of background noise (unwanted audio) from this interview, so the person sounds more on-mic. The net effect here is that sound is acceptable, but the picture has its perspective (and therefore its subject) distorted. It can make people’s heads and their features seem enlarged or out of proportion. Of course any mic can be used to gather natural sound or BG, but for one-person crews, the camera mic is the standard tool for achieving that end. Camera-mounted mics can also be used to collect room tone. Room tone, or ambient sound, is the sound of the room without any speaking or other sounds made by the talent or the crew. It may include the sound of an air conditioning system, the buzz from fluorescent lights, or just the outside noise that leaks into the room. Room tone is essential in the editing process, so always take a few moments with the entire crew on set to call for quiet and record 10 to 30 seconds of room tone.
FIGURE 9.21
The safest way to get good audio when shooting video is to use headphones to monitor the sound.
Boom Microphones
Although most microphones can be placed on a boom, the most common one used on booms is the shotgun. The portable boom or fishpole allows its operator to place the mic in the optimum position to gather the best audio. This is a common way for production crews and larger news organizations to gather audio in the field. Good teamwork between the photographer and the soundperson can keep the mic out of the picture but in the right place to get the best audio. The task of the boom operator is to keep the desired sound source on axis while aiming the mic away from other distracting sounds. In the case of the reporter interviewing people on the street, a fishpole can be used by an audio person to do what a handheld mic does, only without the mic being seen. This gives a more natural, realistic look. The audio person lines the mic up with the person’s mouth at an angle to avoid having it also pointed at, say, the street or an idling car at the curb. Most of the time the mic is at waist level, as close to the person as possible and pointed up. The fishpole can also be held above and pointed down to the audio source, but this increases the possibility of reflected sound being gathered if the ground is a hard surface, such as concrete. (See Figure 9.9.)
Lavaliere Microphones
Lavalieres, lavs, or mini-mics can be the best sounding but most frustrating mics to use in field productions. They are, by far, the most susceptible to mechanical noise caused by material rubbing against the mic or the cable. Extra care is needed when using this type of mic. The most common use of a lav is on someone’s tie, jacket lapel, or shirt. The most common lav clasp is the alligator clip. You simply clip on to any edge or fold of material. The two most common mistakes in using lavs are not hiding the mic cable and not properly securing it.
Viewers are often distracted when they see people being interviewed on TV using a lav that is simply hanging from the front of their clothes. It looks sloppy and inappropriate. This leads us to another problem. It is natural for everyone to move somewhat during a conversation. If the mic is placed incorrectly or the cable is not secured, a little movement translates into a horrendous scratching sound called mic rustle.
You must use considerable care when choosing where to attach a mic to a person. Look for a spot that is not distracting to the camera and will not be brushed against by any part of the person’s clothing or jewelry. Be sure to use all of the alligator clip when securing the lav, not just the front of the clip, as the front of the clip will not hold the mic securely, allowing the mic to slip, move, and rub against clothing. Next, make sure the cable is fastened down so that it cannot pull on the mic. The easiest way is to loop the cord to the back of the alligator clip and pinch it with the material used to hold the mic. The other way is to use a fabric tape or a similar product such as surgical tape (from any drug store) to tape the cable to the inside of the clothing or even the person’s skin. For an active subject wearing a lav, using both procedures is highly recommended.
Many other devices are available for attaching lav mics. The second most popular is the pin or “vampire” clip. This holder attaches to the cable and has two fine stick pins that catch the subject’s clothing. It is used extensively when hiding the mic under clothing. Care must be taken not to damage the material or stick the subject with the sharp pin.
Because lavs are so small, most EFP users prefer hiding them in the person’s clothing. This is not an easy job, but the results are well worth the effort. This mic placement can make everyone wearing one sound good without seeing the mics. This is especially true in a dramatic production, where seeing the mic can ruin the mood. There are many ways to hide a lav that is often no bigger than a small pea. The dangers are clothing rustle and muffling. The mic capsule must be as unobstructed as possible, even if it is already under the clothing. The mic must be taped down with several inches of tape between clothing layers, with the capsule taped on both sides and with only the grill area of the capsule left exposed. If the mic goes between clothing and skin, the mic can be taped directly to the skin using surgical tape or the equivalent. Sometimes a little funnel made of tape or even very soft leather can be fashioned to shield a hidden mic from rustle. This process is tricky and may take some trial and error to perfect.
Wireless Microphones
The distinguishing factor about a wireless mic is not the mic, but the means of transmitting the audio from a mic to a receiver at the recorder. Of all the types of mics, using a wireless has the most dramatic results. Wireless mics allow the audience to hear someone perfectly as though they are “up-close,” even though they are obviously some distance from the camera or are moving about the set or location, without seeing a microphone or cable in the shot.
Combining the use of the wireless with the hidden mic can truly free up your subjects to be as natural as they can be. Wireless mics have become so popular in all forms of EFP that most producers simply will not work without them. They have become as important as, if not more important than, boom mics to get high-quality audio without a mic being on camera. A wireless mic allows the talent to roam the location cable free, to turn backward to the camera while still being on-mic, and to have close-in mic sound. With extensive use of wireless mics, a production can take on a more natural sound, as if the viewers were actually there.
The use of wireless mics has also made quite a difference in news gathering. Veteran news producer Ray Farkas made extensive use of wireless mics on stories for the networks and other news outlets in the 1990s. Farkas was the pioneer in using wireless sound and leading photojournalism into a new sound era. By eliminating the boom mic and placing the camera and crew a great distance from the subject, Farkas was able to relax the video subjects so completely that they forgot they were wearing a mic and being videotaped. The results became known as the “Farkas interview,” an interview that is not only more conversational in tone but actually looks like the viewer is eavesdropping on a private conversation. This technique can make a simple news story more compelling to watch and more convincing. Although no staging is allowed in journalism, the obvious presence of camera, lights, and mics can make an interview look more like a TV show than a slice of real life. Farkas’ highly stylized technique may not suit all or even many of the traditional looks of TV news, but it does represent what attention to the audio-gathering process can do for editorial content.
Even without the more complex uses that Farkas developed, the wireless is an invaluable tool for any everyday news crew. Besides wiring a subject for better natural sound or walking interviews, the wireless can be plugged into PA systems or placed on podiums at meetings and gatherings so that the camera can go anywhere within the location and still have a house audio feed. The wireless can be quickly and easily placed anywhere within a scene to get a close-in presence to the sound.
Even if you cannot plug in directly or put the mic at the source of the audio at an event that has a PA system (public address or house sound), you may be able to place the wireless directly in front of the PA speaker. The audio is not as good as a direct feed, but if the sound system does not have excessive buzz or hum, you can still get house sound. The small size of wireless transmitters allows you to place the mics just about anywhere. If you are shooting a long line of Super Bowl ticket buyers, you might simply set the wireless on the counter at one of the ticket windows. You could then make a shot from anywhere around the window and still have great audio from the activity there. One shot may be from the end of the line with the window in the background as the viewer hears the conversation at the window. This helps focus the viewer on what is taking place. The technique may also be as simple as putting the mic at the stream’s edge for a wide shot of a beautiful valley as canoeists pass through it. The camera is up on the side of a small hill, but the audio is of the water flowing in the stream below and the sounds of the canoeists as they pass through the shot. Synchronous sound that you could not get with the mic at the camera position can now be gathered with creative use of the wireless. This simple and subtle use of close-in sound can make a good video story into a great one.
FIGURE 9.22
This small but versatile audio field mixer can be powered by three AA batteries and is used for EFP or ENG sound recording for video.
MONITORING, MIC PREAMPLIFIERS, MIXING, AND STEREO
After you have selected the appropriate mic, mount, filter, and screen, and achieved proper placement, you need to consider other aspects of the sound-recording process. Multiple microphones for any given sound situation require combining signals, called mixing. To ensure that your sound is appropriate for your situation, you must also learn to monitor the sound. A brief mention is also made here about stereo-sound recording and microphone preamplifiers.
Monitoring
While the performance of your equipment may be well known, you cannot really know if everything is working properly unless you actually hear what you are getting.
A good pair of headphones is absolutely mandatory for any audio or ENG/EFP person, and at least a good ear piece is essential for a one-person operation. Without hearing what you are getting, an unheard problem can make all your efforts worthless. Most professional VCRs offer a confidence playback head in the audio-recording circuit. This system allows you to actually hear the sound on the tape after it has been recorded while you are still recording. The playback head passes over the tape about one second after the record head lays down the audio. Because of this delay, confidence audio sounds weird because it is out of sync with what you are seeing. Most videographers and audio persons only spot-check the confidence circuit occasionally during the recording process because of this distraction. Newer digital recorders do not have this feature and require direct monitoring.
It takes some practice to “hear” audio. Even with a good set of isolation headphones, it is hard to separate the audio you are monitoring and the sounds that are bleeding through the headset. If the headset is turned up too loud, you may think the background noise is excessive when in reality it is not. It takes the experience of doing field recordings and playing them back in the studio to become comfortable with knowing what you’re getting on location.
Microphone Preamplifiers
When a microphone is plugged in to a camera or a mixing console it is always connected to a microphone preamplifier (or mic pre). A mic pre is a special electronic circuit that amplifies the low-voltage, low-impedance signal of a microphone to the appropriate level for recording. ENG/EFP cameras come with an adjustment for audio gain. This is the preamplifier adjustment. All mixing consoles and field mixers have multiple microphone preamplifiers. It is important to take care in adjusting the microphone preamplifier as this is the most likely source for audio distortion if it is turned up too much, or too much gain is added to the incoming signal. As a general rule, adjust the mic pre so that the loudest sound does not distort and your average level approaches zero on the audio meters.
Mixing
The last stage that the audio signal is likely to go through is some form of mixing before it is recorded. To mix audio, it first needs to be monitored. Whenever more than one mic is being recorded on a single audio channel, it is best to use a mixer to make sure each mic can be separately controlled to ensure the best blend of audio sources.
Popular professional, portable mixers have three or four input channels, filters that will cut out certain audio frequencies, a tone generator, two output lines, and a master output volume control. They can take line or mic level impedance inputs and send mic or line level out. They can also feed phantom power to condenser-type mics on any channel. Most importantly, they are usually stereo, with each channel capable of being panned or adjusted to the right or left. This ability lets the operator place only the audio of channel 1’s input on the channel 1 output by panning channel 1 to the left. Panning channel 2’s control to the right would place its audio on the channel 2 output only. Additional channels can also be panned to either output channel. The audio person then has the flexibility of isolating or combining signals to the recording tracks in the camera.
These portable mixers are very popular for use with camcorders. Two record channels on the recorder can be set up with a tone signal from the mixer; the input volume adjustments can be made at the mixer, and no further attention is required at the camera. In some cases, the sound person will use a wireless mic to send the output of the mixer to the camcorder, thus allowing the photographer to roam freely while the audio person can go wherever the best sound-gathering location is.
Stereo
Stereo audio is most common in performance videos and is not practical for most ENG and EFP shoots. In EFP production, stereo sound is usually added in postproduction, where the variables are controlled and the source material is dependable. Such factors as the mics used and critical mixing techniques make stereo recording a very demanding job in the field. More effort is required at the time of recording than most productions can afford—and typical news gathering generally does not allow the time needed for stereo recording.
SUMMARY
Professional videographers know that the quality of the video project depends not only on the pictures, but also on the sound. Collecting sound for your video work is important—audiences know when the sound is not right. Selecting the best mic and using proper technique will help to make your video project look and sound more professional.
Microphones have been used in electronic media for over 135 years, beginning with Alexander Graham Bell’s telephone in 1876. Although many advances in mic structure and design have occurred, the mic’s basic function of collecting accurate sound has stayed the same over the years.
Microphones used in most professional situations have two types of construction: dynamic or condenser. Dynamic mics generate sound when sound waves strike a moveable coil of wire inside the mic, creating a small electrical signal. Condenser mics have a positive (+) and a negative (−) electrode inside of them. When sound strikes one of the electrodes, the distance between the two electrodes changes, resulting in a small electrical signal. In both of these designs, the small electrical signal becomes the sound signal. Microphones can also be differentiated by their impedance (resistance to signal flow) and their style (e.g., handheld, lavaliere, stand-mounted). Some microphones are used for special applications, such as when you are trying to collect audio from a moving singer/performer, multiple speakers, or in situations where microphone cables won’t work and a wireless mic is needed. There are a variety of cables and connectors that can be used in video production work, and selection of the appropriate equipment requires knowing the application and the advantages and disadvantages of the connectors. Most mics are designed to be placed and used in specific ways, so knowing how these mics work and how to place them on location will help you to collect accurate and appropriate audio. The best way to ensure that you are collecting good audio is to always monitor your audio. In the field, make sure that you wear headphones connected to your recorder to guarantee that the sound being recorded is the sound needed for your professional production.