DA. See distribution amplifier.

D/A. See digital-to-analog converter.

DAC. See digital-to-analog converter.

DAE. Digidesign Audio Engine. An application that runs in the background on a computer and provides communication between audio software, such as Pro Tools, and Digidesign hardware and audio interfaces. DAE manages the transfer and processing of all the digital audio in the system.

daisy chain. A serial wiring arrangement where device one connects to device two, which connects to device three, which connects to device four, and so on. A MIDI system connected by wiring the thru of each device to the input of the next device is an example of a daisy chain. See Figure D.1.

Figure D.1. MIDI equipment is often connected together in daisy-chain fashion, MIDI thru to MIDI input.

damp. See damping.

damper. A weighted felt pad in an acoustic piano that mutes the string, or stops it from vibrating. When a key is played or the sustain or sostenuto pedal is pressed, the damper is lifted and the string is allowed to ring.

damper pedal. See sustain pedal.

damping. Muting a signal or reducing its vibrations in level. Examples of damping can range from a muffler on a drum head to acoustic absorbers in a studio.

damping factor. The ability of an amplifier to control unwanted speaker movement. Since a speaker’s voice coil is a coil of wire in a magnetic field, whenever a speaker moves it actually generates a small amount of current, which feeds back to the amplifier. If the amp’s impedance is low (damping factor is high), the motion of the speaker will stop quickly. Low-frequency drivers are most affected by damping factor. Other factors can affect an amp’s damping factor, such as speaker cable resistance, a passive crossover between the speaker and the amp, and the resonant frequency of the speaker.

DASH. Digital Audio with Stationary Head. A stationary recording head technology used for early reel-to-reel large-format digital recorders from Sony and Mitsubishi. DASH recorders were available in 2-, 24-, and 48-track formats.

DAT. Digital Audio Tape, a.k.a. R-DAT. A rotating head, helical-scan, stereo digital audio recording format that used tape cassettes somewhat similar to video cassette tapes (though much smaller). The DAT standard supported four resolutions/sample rates: 12-bit/32 kHz, and 32, 44.1, and 48 kHz at 16 bits. Digital audio is recorded to DAT without any data compression or other processing, which made it a popular mixing and mastering format. Rackmount and portable field-recorder units were available for professional use, and a few models were released for consumer use as well (though consumer DAT was a complete flop).

data. Literally, information.

data compression. A wide variety of techniques for reducing the size of data files in order to conserve disk space or transmission bandwidth. There are two broad categories: lossless, which uses statistical algorithms to reduce file size without compromising data quality or accuracy, and lossy, or perceptual coding, which removes unessential data to reduce file size with limited impact on accuracy. There are a variety of types: JPEG (for graphic image files); FLAC, MPEG-2, MPEG-4, and AAC (for audio files); and many others.

data encryption. Encryption is a method of encoding or transforming information so that only those who possess the key can understand it. Data encryption is used to protect the privacy and confidentiality of information stored on computers.

data spanning. A feature of some CD- and DVD-burning programs that can spread a data file that is too large to fit on a single disc across two or more discs.

data transfer rate. The average number of bits or blocks of data being transferred in a given amount of time. In other words, how fast data is transmitted between devices. See also bit rate.

DAW. Digital Audio Workstation. A digital device or system that can be used to record, edit, mix, and process audio signals (see Figure D.2). There are three basic components to a DAW: digital audio software, analog-to-digital and digital-to-analog converters, and a computer. In some cases, these components are integrated into a single standalone device. In other cases, a computer is used as the base platform for the system. Digital audio workstations were developed as early as the 1970s, but the technology really grew to widespread prominence in the late 1990s. Several of today’s computer-based DAWs grew out of MIDI sequencing programs developed in the ’80s and ’90s, including Opcode Studio Vision, MOTU Digital Performer, Steinberg Cubase and Nuendo, Apple Logic, Cakewalk SONAR, and others. Digidesign Pro Tools, Sony Creative Software ACID, Ableton Live, and others were not based on sequencers, though they now include extensive MIDI features.

Figure D.2. A DAW can record, process, edit, mix, and play back audio.

dB. See decibel.

dB SPL. Also known as dB, though this is an incomplete reference without the “SPL” identifier. A decibel reference for sound pressure level. All decibel “measurements” are actually ratios against a particular reference. In the case of dB SPL, the reference is the accepted threshold of human hearing, or 20 micro-pascals of sound pressure. At the other end of the scale, 130 dB SPL is considered the threshold of pain. The optimal listening level for studio recording and mixing is around 85 dB SPL, a level that allows for safe long-term listening and that also provides the most even frequency response from our ears. Note that decibels and sound pressure levels are related in a logarithmic fashion—this is because the span between the softest and the loudest sounds we can hear is so huge as to be unwieldy. Decibel ratios allow this huge span to be represented in a more compact way. See Table D.1.

DB-9. A 9-pin audio connector. See also 9-pin, D-sub.

DB-25. A 25-pin audio connector. See also D-sub.

dBFS. Decibel Full Scale. A decibel reference that is equal to the maximum voltage level that can be sent into an analog-to-digital converter without clipping. Full scale, or full code, refers to all the bits in a digital word being utilized to represent a signal’s level; any higher level will result in distortion. In most digital systems, 0 dB is the full-scale reference, though there may or may not be some headroom built in above this reference in the system. Note that 0 dBFS is not the same as 0 VU or 0 dB in an analog system. Different digital systems reference analog 0 dB to various digital levels, such as –18 or –14 dB. See Figure D.3.

Figure D.3. A digital meter reads 0 dB as the highest possible level before overload (right), unlike a VU meter. A signal that reads zero on a VU meter typically reads –18 dB or –14 dB on a digital meter (left). Many experts recommend –18 as the best level for recording into 24-bit digital audio systems, as it allows plenty of room for clean transients.

dBm. Decibels referenced against one milliwatt of power, usually into a 600-ohm load. A value of 0.775 volts will produce one milliwatt at 600 ohms; this is the 0 dB reference point for power levels in mixers, recorders, and other audio equipment.

dBu (a.k.a. dBv [small “v”]). Decibels referenced against voltage—in this case, 0.775 volts—but without referencing an impedance load. At 600 ohms, 0 dBu is the same as 0 dBm, but many pieces of gear use impedances much higher than 600 ohms, so dBu usually ends up referenced against just voltage. In mathematical terms, the dBu ratio (all decibel ratings are ratios between two things) is calculated using 20log(V2/V1), where V1 is the 0.775 reference voltage, and V2 is the voltage for the dBu being calculated. For example, plugging in 1.23 volts, or 20log(1.23/0.775), gives a result of +4 dBu, the nominal input and output level for professional equipment. See also dBV.

dBV (large or capital “V”). A decibel reference similar to dBu, referenced against voltage without an impedance load. The difference between dBu and dBV is the reference voltage level. Where dBu references 0.775 volts, dBV references 1 volt. In mathematical terms, the dBV ratio (all decibel ratings are ratios between two things) is calculated using 20log (V2/V1), where V1 is the 1.0 reference voltage, and V2 is the voltage for the dBV being calculated. With a voltage of 0.316 volts, or 20log (0.316/1), we get –10 dBV, the nominal input and output level for semi-professional equipment. See also dBu.

dbx. 1. A manufacturing company that specializes in dynamics and noise reduction processors. 2. A type of analog noise reduction system that compresses signals as they are being recorded to analog tape, then expands the signals as they play back from tape. The expansion process restores the compressed signal while simultaneously pushing down any noise originating on the tape. There are two varieties of dbx noise reduction. Type I is intended for wide-band recordings, while Type II has greater “pre-emphasis” in the high frequencies, making it better for video tracks, telephones, and other applications.

DC. See direct current.

DC offset. A constant direct current voltage in an audio signal (which by nature is alternating current, or AC) that results from component imperfections or imbalances in an analog-to-digital converter. DC offset is a problem because it reduces the available headroom for the signal and can result in clicks and pops when an audio file is edited.

DCA. Digitally Controlled Amplifier. An amplifier module in a synthesizer or sampler whose gain is controlled digitally rather than using analog voltages. This allows for much more accurate and fine control, with better repeatability. See also VCA.

DC-coupled. An analog circuit in which the components are directly connected together, without capacitors between them. This has advantages; it has better low-frequency response, there is no change in the sound over time since there are no capacitors to degrade, and there is a linear phase relationship between channels in multichannel devices, such as mixers. However, the lack of capacitors means there is nothing to protect the circuit from unwanted DC voltage in the signal, which can cause distortion.

DCF. Digitally Controlled Filter. A filter module in a synthesizer or sampler whose parameters are controlled digitally rather than using analog voltages. This allows for much more accurate and fine control, with better repeatability. See also VCF.

DCO. Digitally Controlled Oscillator. An oscillator module in a synthesizer or sampler whose frequency is controlled digitally rather than using analog voltages. This allows for much more accurate and fine control, with better repeatability and tuning stability. See also VCO.

DDCD. Double-Density Compact Disc. A CD format specified in the Purple Book. DDCD has a storage capacity of 1.3 GB, double that of a regular CD. This is achieved by increasing the density of tracks and pits used to store data in the optical media. DDCD was conceived as a stopgap to help delay DVDs making CDs obsolete, but it was never successfully launched to the public.

DDL. Digital Delay Line. A digital device that can capture a discrete copy of a signal and replay it after a certain amount of time has elapsed, creating an echo effect.

DDR. Double Data Rate. A type of DRAM computer memory chip that is similar to SDRAM but transfers data twice as fast.

dead. A space in which all or most acoustic reflections are absorbed. The ultimate dead space is an anechoic chamber, which is specially constructed and treated to absorb all reflections at all frequencies.

decay. 1. The manner in which sound falls to silence. 2. A parameter in an envelope generator (for example, ADSR) that controls the drop from the attack’s peak level to the note’s sustain level.

decay time. See reverberant decay.

Decca Tree. A stereo-miking technique developed at Decca Records that uses three omnidirectional microphones. (Traditionally, Neumann M 50 small-diaphragm tube condenser mics are used.) The microphones are mounted to a T-shaped bar (although three mic stands could also be used), with two microphones spaced two meters apart on the sides of the T, and the third mic placed 1.5 meters in front of the side microphones and centered between them (see Figure D.4). The Decca Tree arrangement is most often used for orchestral and film-score recording. It provides a solid stereo image that holds up well under Dolby surround processing.

Figure D.4. Decca Records developed the Decca Tree, a three-microphone stereo technique using omnidirectional microphones placed in a T arrangement.

decibel. 1. One-tenth of a Bel. 2. The ratio between two audio levels. A decibel is an expression of the ratio between an audio signal and a 0 dB reference, and not actually a measurement of audio level. Because of the way in which our ears respond to volume, these ratios are logarithmic in nature. 3. The smallest volume change the human ear can perceive without a reference to compare against, in isolation. See Table D.2.

decimation (a.k.a. downsampling). A process that converts an oversampled digital signal into a digital signal at a standard sample rate by strategically dropping samples. For example, a 44.1-kHz CD sample rate might be oversampled at 64x, resulting in a sample rate of 2.8224 GHz. Decimation is used to reduce the rate back to a standard 44.1 kHz. This is a two-stage process. First, the signal is low-pass filtered to prevent aliasing, then it is downsampled or reduced in sample rate.

deconvolution. In convolution reverbs, a sweep, gunshot, or other impulse signal is used to excite an acoustic space so that the space’s sound can be captured and used to create an impulse response, or IR. The IR is used to calculate reverb effects based on the actual sound of the space (a process called convolution). To use the impulse response, the sweep, gunshot, or whatever sound was used to excite the space must be removed from the raw captured sound of the space. The process of removing the sound is called deconvolution.

decorrelation. In audio, using delay, reverb, or other processing to convert an audio signal to stereo or multichannel surround. Decorrelation was originally a technique used by older THX home theater systems to stereo-ize the mono rear channel signal to feed both rear surround channel speakers. Stereo reverbs also use decorrelation to create differences between the two channels, resulting in a more spacious effect.

decoupling. Isolating an object, such as a speaker cabinet, monitor, or even a room’s floor or wall, from its surroundings to prevent the transfer of vibrations or resonances.

de-esser. A dynamics processor that is set up to respond to high frequencies in order to reduce the levels of sibilants in a signal. (Controlling sibilants can be a creative choice to make a track sound better or a necessity to reduce high-frequency distortion.) A number of dedicated de-esser hardware and software units have been released, or any compressor with a sidechain input can be made into a de-esser by routing the audio signal to both the audio input and the sidechain input and boosting the high frequencies of the sidechain input using an equalizer. This makes the compressor more sensitive to high frequencies, particularly “s,” soft “c,” and other sibilant sounds. See Figure D.5.

Figure D.5. To create a de-esser from a compressor, route a signal to both the compressor’s audio input and its sidechain input. Use an equalizer to boost the high frequencies of the signal feeding the sidechain input.

default. The original, out-of-the-box settings for a device as it comes configured from the manufacturer.

de-install. See uninstall.

delay. 1. Also known as echo. A discrete repeat of a signal at some period of time after the original signal is played. 2. A device that captures a signal, holds it for a certain period of time, then plays it back to create an echo effect. 3. A side effect of latency, or the period of time it takes for a process to take place or for a signal to pass through a signal path. Latency-related delay is a problem when monitoring signals during tracking or overdubbing, or when performing live.

delay compensation. A function of some DAWs that coordinates the timing of signals or DAW tracks to compensate for the delays created by plug-in processing or other latencies. The idea is to restore the proper timing between those tracks or signals so they play back in sync with one another.

delay time. In an echo or delay effect, the amount of time that elapses between the original sound and when the delayed sound is heard.

delete. To erase a file from a hard drive, a quantity of text from a document, or an audio segment from a track, or to otherwise remove data from a document, session, or computer.

demagnetizer. As analog tape is recorded or plays back, the magnetism on it tends to slightly magnetize the metal parts of the recorder it passes. Over time, accumulated magnetism on these parts can degrade the audio contained on other tapes as they are recorded or played. A demagnetizer is a device that removes any magnetism that may have built up on the heads and other tape machine components. Demagnetizers must be handled with care to effectively demagnetize the desired items without affecting things that should not be demagnetized (such as tapes and hard drives).

demo. Short for demonstration. 1. In music/studio terms, “demo” refers to a rough version of a recorded musical piece created to test or evaluate the piece or to use as an example of the work to play for others. 2. A product offered for sale that a retailer or manufacturer has used for demonstration purposes and that is therefore not in strictly new condition.

density. See diffusion.

desktop. A part of a computer’s operating system graphical user interface analogous to the surface of a physical desk. The desktop is the basic screen “surface” displayed on the monitor screen. It can show background pictures and graphics; icons for hard drives, files, and programs; as well as other items.

destination. The parameter to which a modulation signal or message is routed.

destructive editing. Audio editing or processes that permanently modify or overwrite the original file. In many cases, there is no undo command or function to restore the original file after destructive editing takes place. The only way to get back to the original file is to make a backup copy of it first, before destructive editing takes place. Fortunately, most DAWs and audio programs offer non-destructive editing and processing that does not destroy the original audio data.

destructive recording. Audio recording or overdub-bing that permanently modifies or overwrites a preexisting file. In many cases, there is no undo command or function to restore the original file after destructive recording takes place. The only way to get back to the original file is to make a backup copy of it first, before destructive recording takes place. Fortunately, most DAWs and audio programs offer nondestructive recording that does not overwrite older audio data when new data is recorded.

detector. See sidechain.

detent. A notch in the travel of a potentiometer or fader that indicates a certain setting, such as zero, the center position of a pan pot, or a nominal level.

detune. Slightly pitch shifting a signal up or down, usually by five or fewer cycles per second. The detuned, or pitch-shifted, version of the signal is often mixed back in with the original un-pitch-shifted signal, creating a chorus-like effect resulting from beating and very slight playback speed differences between the two versions of the signal. A common production trick is to pan the dry, un-shifted signal in the center, to pan a version pitch-shifted up by a few cents to the left, and to pan a version pitch-shifted down by a few cents to the right. This creates a wide, rich effect useful for thickening signals.

device aggregation. See aggregate device.

device driver. A small piece of software that allows software applications to access peripheral hardware devices connected to a computer.

DFD. Direct From Disk. A proprietary technology developed by Native Instruments for playing large samples directly from a hard drive without having to load them completely into RAM first. A small amount of RAM is used to pre-load or buffer the samples to compensate for hard-drive latency.

DI. Direct Injection. See direct box.

dialog. An alert or window that opens in a software application and that contains a message to, or requests an action or input from, the user.

dialog box. See dialog.

diaphragm. A very thin circular (other shapes are very rarely used) sheet of metal or metal-coated Mylar held under tension in a microphone capsule. The diaphragm moves in response to air-pressure changes resulting from sound waves. The diaphragm motions either move an attached coil of wire in a magnetic field or change the distance relative to a charged plate to create electrical signals analogous to the sound waves.

diaphragmatic trap. See membrane trap.

die. A small piece of semiconductor material containing an integrated circuit.

dielectric (a.k.a. insulator). A material that does not conduct electricity.

difference tone (a.k.a. combination tone). A frequency created under certain circumstances when two other frequencies are sounded together. The new frequency will be at the difference between the two original frequencies. For example, the difference in tone created by two tones at 500 and 300 Hz would be at 200 Hz.

differential. See balanced. The term differential is usually used in reference to computer cabling.

diffraction. In acoustics, diffraction is the tendency of sound waves with long wavelengths to bend around objects (to diffract) instead of reflecting off them.

diffuse. Scattered or spread out.

diffusion. 1. In acoustics, the process of breaking a single reflection into many smaller, lower-level reflections and scattering them in different directions. This reduces the intensity of the reflection and helps to reduce acoustic interference problems. 2. With artificial reverbs, a parameter that sets how dense or “thick” the reverb effect sounds. Also known as density.

diffusor (a.k.a. diffuser, though the “diffusor” spelling is more commonly used in acoustics). An acoustic device that scatters sound waves (see Figure D.6). See also diffusion.

Figure D.6. A diffusor breaks up and scatters reflections to reduce acoustic interference problems.

digital. Signals or information stored and transmitted as series of discrete, non-continuous electrical impulses representing digits (numbers) rather than as a continuous analog voltage.

digital 0. On a digital meter, 0 is the highest level possible, at the top of the meter. At 0, all of the bits for the digital signal are turned on, so any signal higher than that will be clipped or distorted (although some systems do scale digital 0 down a small amount to allow for some headroom). Note that digital 0 does not equal 0 as indicated by an analog VU meter. Various manufacturers calibrate their systems so that 0 VU equals –18 dB, –14 dB, or another level on the digital meters to allow for sufficient headroom when recording transient materials, such as drums. See also dBFS.

Digital Audio Workstation. See DAW.

digital black. In audio, a digital signal with no audio present or a volume of zero. In video, a digital signal with a pure black picture. The digital signal still carries all subcode and clock information; there is simply no “content.”

digital synthesizer. A synthesizer that uses digital signal processing (DSP) to create sounds, rather than generating and modifying electrical voltages like an analog synthesizer. Digital synthesizers are available as standalone hardware units or as virtual software synthesizers that run on computers or in DAWs.

digital-to-analog converter (a.k.a. D/A, DAC). A device that converts a digital representation of an audio signal into an analog voltage.

dim. A function on many mixers that automatically reduces the monitor output levels when the talkback microphone is used. Some mixers also have a dim control that reduces the monitor level when pressed to allow for easier conversation in the control room. On some mixers, the amount of dim level is fixed; on others, there is a control for setting the dim level.

DIMM. Dual In-line Memory Module. A type of computer SDRAM memory expansion board that contains several RAM chips. A DIMM is essentially a double SIMM that provides a 64-bit data path. There are many versions, ranging from 72-pin to 240-pin, different form factors, and more, all available in a range of total memory capacities. See also SDRAM, SIMM.

DIN. Deutsche Industrie Normung, Deutsche Institute fur Normung, or Deutsche Industrie Norm. A standards organization in Germany. DIN standards are used for different plugs and connectors (a MIDI connector is a DIN connector), as well as a variety of noise, signal, and rack measurements.

DIN stereo. A stereo microphone technique where two cardioid microphones are placed 20 cm apart, angled at 90 degrees (see Figure D.7). Because cardioid microphones are used, the mics must be carefully placed in relation to the sound source to avoid inaccurate low frequencies due to proximity effect.

Figure D.7. With the DIN stereo mic technique, two cardioid microphones are positioned 20 cm apart, at a 90-degree angle.

DIN sync. See Sync 24.

diode. An electronic component that only passes current in one direction. Diodes are used in power supplies and other applications. A special type, the LED (light-emitting diode) produces light when current passes through it.

dip. An area where cancellation of sound waves causes a decrease in level at a particular frequency or range of frequencies.

DIP switch. Dual In-line Package switch. A type of compact slider switch designed to be mounted on a printed circuit board inside a device. Often there are a number of switches in a signal DIP module, which are used to semi-permanently set up rarely accessed parameters that define the operation of the device.

direct box (a.k.a. DI). A device used to convert high-impedance unbalanced signals to low-impedance balanced signals. Direct boxes can be either active (using a powered preamplifier) or passive (using transformers), and may include other features such as ground lift, polarity invert, and others. In the studio, a direct box is used to connect an instrument-level signal, such as an electric guitar or bass, to a mixer or preamp microphone input. Live, direct boxes are used to run the outputs from instruments such as guitars and electronic keyboards through a snake to the front-of-house mix position.

direct field. Speakers or a sound source set up so that the listener primarily hears the direct sound, with few or no reflections and little reverb. See also near field.

directional. 1. Moving in a single direction. 2. A type of microphone that is sensitive to sound coming from one or more directions (such as in front of the mic) and not sensitive to sound coming from other directions (such as from the sides or rear of the mic).

direct out. An output connection on many mixers that routes a single channel out of the board. A direct out taps off the signal before it is bused to subgroups or master outputs (see Figure D.8). In some cases the signal is taken directly after the mic preamp, after the EQ, after the channel fader, or other points in the signal path. Direct outs are most commonly used to feed a channel’s signal to a recorder or DAW input, although they can be used to send the channel anywhere desired.

Figure D.8. Direct outs on a mixer tap off the signal before it is bused and send it back out to another destination, such as a recorder or interface input.

direct radiator. A speaker that does not use a horn design for interfacing the driver with the air. Direct radiators can provide smoother sound than horn designs, but they are not as efficient and they lack the directivity and throw. For this reason, direct radiators are often used for studio and home use, while horns are often used for PA systems.

direct recording. Recording without using microphones, by routing signals from electronic instruments or from pickups on acoustic instruments straight into a mixer or recorder.

direct sound. Sound from a source that arrives at the listener’s ears without reflecting off any surfaces.

DirectSound. A type of DirectX software developed by Microsoft for managing, capturing, and playing audio through soundcards in the Windows operating system. DirectSound provides a direct connection between audio applications and soundcard and audio interface drivers.

Direct Stream Digital (a.k.a. DSD). A technology jointly developed by Sony and Philips for recording and playing digital audio intended for the companies’ jointly developed SACD format. Direct Stream Digital uses a 1-bit oversampling approach with sample rates as high as 2.8224 or 5.6448 GHz. Frequency response for Direct Stream Digital systems is typically 0 Hz to 120 kHz, with 120-dB dynamic range. See also 1-bit.

DirectX. 1. A family of protocols developed by Microsoft for use in Windows audio, graphics, game, and multimedia applications. 2. In audio, DirectX is the name given to a format for plug-ins that can be used in real time within Windows DAWs and other audio software, or, depending on the plug-in, may work off-line (in non-real-time).

dirty. A signal containing harmonic distortion (intentional or not!) or noise.

disc. Optical storage media. See also disk.

disc-at-once. A Red Book compact disc burning mode in which the entire disc is written at one time, in a single pass, without turning off the laser. Burning a CD with disc-at-once prevents imperfections on the CD caused by turning the laser on and off. These imperfections don’t cause problems for most CD players, but they can cause errors for a disc replicator if the CD is being duplicated for distribution. See also track-at-once.

discrete. Literally, separate. In electronics, discrete refers to using separate, individual components to create a circuit rather than using integrated circuit chips. With a discrete circuit, the designer can select each component, optimize interactions, and customize the final results, as opposed to using the pre-packaged design in an IC chip. Discrete designs generally are more expensive, require more room, take more time to create, generate more heat, and use more power, but they are considered by many musicians and engineers to have superior sonic quality.

disk. Magnetic storage media. See also disc.

disk cache. See buffer.

disk image. See image.

dispersion. 1. Scattering or distribution of sound waves as they travel from a sound source, such as a speaker. 2. The angle of coverage a speaker can produce. There are two dispersion characteristics for speakers: vertical and horizontal.

distant miking. Placing a microphone more than a few feet from a sound source. Distant miking will capture more of the room ambience along with the source, and with directional microphones generally will have more natural frequency response.

distortion. Literally, any change in a signal other than making it louder or softer. This would include equalization, compression, and other forms of processing. But in practice, distortion tends to be considered a negative or undesirable change in a signal’s waveform.

distribution amplifier. (a.k.a. DA). A specialized type of amplifier used to split a signal so that it can properly feed multiple devices.

dither. In audio, dither is low-level noise intentionally added to a digital audio signal. At very low levels, a digital audio system can have difficulty determining whether the last few bits should be on or off, resulting in quantization noise. A small amount of noise—dither—can cause the bits to positively turn on and off, making softer audio signals clearly audible and fade-outs to silence smoother. Dither is usually used in the final stages of production, such as when reducing the bit depth of a signal from 24 bits to 16 bits for creating a final CD.

divergence. A control found in some surround panners that determines how much of a signal sent to the front goes to the left/right speakers and how much goes to the center channel. In practical terms, divergence determines the “width” of a center-panned signal in a surround mix.

DLL. Dynamic Link Library or Dynamically Linked Library. In Windows operating systems, a collection of software resources that is available to other programs. In Mac OS X, DLLs are known as shared libraries.

DLS. Downloadable Sounds. A specification developed by the MIDI Manufacturers Association that provides a format for loading samples into wave-table-based synthesizers. Because the sample files are small, DLS works well for multimedia and game audio, as well as for web audio, where fast delivery is required. There are several levels of DLS (Level 1, Level 2, and so on) that add features and different methods of synthesis.

DMA. Direct Memory Access. A feature that allows hardware devices (disk drives, sound cards, video cards, and so on) to directly access memory locations without going through the computer’s CPU. In some cases, DMA is also used to transfer data among the memory locations within the computer. In most computers, DMA is arranged into channels, with each channel allocated to a device. See also UDMA, an enhanced version.

documentation. The manual and other instructional and information items that come with a piece of software or hardware.

Dolby. Short for Dolby Laboratories. A company founded by physicist Ray Dolby in 1965 that specializes in noise reduction and stereo and surround encoding hardware and software. Some of the formats created by the company include:

dome tweeter. A type of high-frequency driver composed of a voice coil suspended in a magnetic field that moves a dome-shaped diaphragm to create sound waves. Various materials are used for the dome, including titanium, beryllium, stiffened silk fabric, and more. Factors such as stiffness, low mass, and damping are important, as is lack of ringing or resonance. See also tweeter.

dongle. A hardware copy-protection key that attaches to a computer, usually using a USB port, and allows use of a piece of software. Without the dongle, the software will not run, or it may run in a limited demo mode.

Doppler effect. (a.k.a. Doppler shift). Named for Christian Doppler, a German physicist. The Doppler effect is the apparent change in the pitch of a sound as the source moves toward or away from the listener. Think of a car blowing its horn, and how the pitch goes up as it drives toward you, then falls as it drives away. The Doppler effect is the basis of how rotating speaker cabinets, such as Leslie speakers, create their effect.

DOS. Disk Operating System. The part of an operating system that controls and manages disk drives.

double. 1. See doubling. 2. See double precision.

double-busing. A feature found on some recording mixers that essentially sends the output of a subgroup or bus to a pair of duplicate outputs, sort of like a built-in Y cable. For example, on an eight-bus mixer, subgroup 1 would feed outputs 1 and 9, subgroup two would feed outputs 2 and 10, and so on. This allows the outputs of an eight-bus mixer to be permanently connected to 16 inputs on a recorder or interface, reducing the need for a patch bay.

double fast. A standard for using a single AES/EBU cable to carry stereo 96-kHz digital audio. The AES spec provides for stereo (two-channel) audio at sample rates up to 48 kHz on a single cable. The double-fast standard increases the data rate so that a 96-kHz stereo signal can be carried over a single cable. See also double wide.

double precision. A computer numbering system that uses twice as many bits to represent a number as a single-precision system. For example, a double-precision system would use 32 bits to store a number that would require 16 bits in a single-precision system. The extra bits increase not just calculation precision and accuracy, but also the resulting magnitudes that can be stored.

double tracking. Double tracking is recording the same part twice, to separate tracks. The two takes will not be exactly identical, so there will be timing and pitch differences between them. When the tracks are mixed, this results in a thicker, richer sound, or if they are panned opposite one another, a wide, full sound. See also doubling.

double wide. A standard for using two AES/EBU cables to carry stereo 96-kHz digital audio. The AES spec provides for stereo (two-channel) audio at sample rates up to 48 kHz on a single cable. The double-wide standard splits a 96-kHz stereo signal so that each AES cable carries half the data. See also double fast.

doubling. 1. See double tracking. 2. Using a short delay effect to simulate the effect of double tracking. Delay times are in the 10 to 50 ms range, short enough to not be heard as a discrete echo. A track is recorded, then during mixdown, sent through the delay. The delayed and original signals are mixed together or panned opposite one another in the stereo field.

downsample. To convert a higher sample rate to a lower sample rate. See also decimation.

downward expansion. Expansion is the opposite of compression, in this case applied as a form of noise reduction. When a signal falls below a certain threshold level, downward expansion pushes the signal down by a certain amount, set as a ratio. For example, with a 1:3 ratio, for every decibel the input signal falls below the threshold, the expander will push the output signal down by 3 dB. By carefully setting the threshold and attack and release parameters so that desired signals are not affected, unwanted noise between sounds, such as hiss and hum below the threshold, can be reduced.

drag and drop. A technique used in computers with GUI (graphical user interface) operating systems, where the user positions the mouse pointer over an icon, clicks the mouse button and holds it down, drags the icon to another location (usually a window or an application icon) by moving the mouse while keeping the mouse button pressed, then releases the mouse button.

drain. A bare wire inside a shielded cable that is used to more easily connect the shield to ground or to a component.

DRAM. Dynamic Random Access Memory. A type of RAM that uses capacitors in an integrated circuit chip to store bits of data, one bit per capacitor. DRAM differs from SRAM (Static RAM) in that the charge in the capacitors fades and must be refreshed after a certain period of time. The advantage is that DRAM is simpler and more compact per bit than SRAM. DRAM chips are combined onto circuit board modules, such as SIMMs, DIMMs, and other types, to make installation easier.

drawbar. A sliding bar on a Hammond organ that controls the volume of a particular tonewheel. Sliding the drawbar out increases the volume, while pushing it in lowers the volume of its tonewheel. By adjusting the blend of the tonewheels using the drawbars, different tonalities can be achieved.

drive. 1. Short for hard drive. 2. The amount of gain applied to a signal.

driver. 1. The element of a speaker or monitor that creates sound waves. 2. Software for interfacing peripherals with a computer. See device driver.

drop frame. A system for correcting for the fact that color NTSC video has 29.97 time code frames per second. To compensate for the missing 0.03 frames per second and to make synchronization between devices work out properly, two frames are dropped from the time code every minute, except for every tenth minute.

drop-down menu. See pull-down menu.

dropout. An area of an analog tape that contains no signal. Dropouts can occur for a variety of reasons, including tape inconsistency and the shedding of magnetic material from the tape.

drum grid. A graphic editor window in a sequencer or DAW that is designed to make programming drum and percussion rhythms faster and easier. The vertical axis of the grid represents the individual drum instruments, while the horizontal axis represents time. Notes can be inserted and deleted from the grid to create rhythms, and often the velocity and other parameters of the notes can also be adjusted graphically. See Figure D.9.

Figure D.9. A drum grid editor in a sequencer or DAW provides an easy way to program and edit MIDI drum parts—simply mark the square in the rhythmic grid where you want a hit to occur.

drum machine. An electronic musical instrument designed to create drum and percussion sounds through synthesis or sample playback, and to sequence or record and play back rhythms using those sounds. A drum machine often includes pads or buttons for manually playing its drum sounds or entering rhythms into the internal sequencer.

drum overheads. One or more microphones placed over a drum kit to capture the sound of the cymbals along with the sound of all the drums and a small amount of room ambience (depending on how high the mics are above the cymbals and drums). Typically, the overhead mics are mixed with individual mics on some or all of the drums to create a complete picture of the overall drum sound.

dry. A sound or signal without reverberation or other processing on it.

DSD. See Direct Stream Digital.

DSP. Digital Signal Processing. An algorithm designed to perform mathematical operations on various data types. Audio applications use DSP algorithms that have been designed to produce audio signals and to process digital audio signals in a variety of ways, such as with equalization, compression/limiting, mixing, reverb, and more. These algorithms might run on the computer’s CPU, or they may be designed to run on DSP chips that have been added to the computer via an expansion card or in an external box.

DSP chip. Digital Signal Processing chip. An integrated circuit chip optimized for running DSP algorithms to process data.

D-sub. Short for D-subminiature, a.k.a. DB connector. A multi-pin connector type used on some professional audio equipment. The connector is roughly D-shaped and can carry a number of channels of signal. For example, a DB25 connector, with its 25 pins, can carry eight balanced signals. Other common sizes include 9-pin (commonly used for synchronization and control signals) and 50-pin. D-sub connectors and multichannel cables are used to save space, make cable routing easier, and help organize and group like signals.

DTRS. Digital Tape Recording System. A family of multitrack digital audio tape recorders developed by TASCAM in the early 1990s, including the DA-88, DA-38, DA-78HR, and DA-98. Along with Alesis ADATs, DTRS digital recorders were arguably responsible in large part for the price versus technology revolution that led to the rise of affordable high-quality home and project studios. DTRS tape machines could record eight tracks with 16-bit (later models supported 24-bit) resolution to Hi-8 videotapes. The native sample rate for DTRS machines was 48 kHz, though varispeed could be used to achieve a 44.1 kHz sample rate. Multiple DTRS machines could be linked together for increased track count, resulting in the MDM (modular digital multitrack) system.

DTS. Digital Theater Systems. A company that developed the DTS digital 5.1-channel surround sound system for commercial and home theater use. DTS has also released a number of audio-only 5.1 surround sound music albums on encoded compact discs.

dual concentric (a.k.a. coaxial, point source). A type of speaker where the tweeter is mounted in the center of the woofer and the sound all radiates from a single point. Using a dual-concentric design causes the sound of all frequencies to arrive at the listener’s ears simultaneously, reducing slight colorations sometimes heard with “regular” speakers.

dual core. Two independent computer processors mounted on a single chip. The advantages to doing this over having two separate chips include compact size, reduced power requirements, reduced heat, and the ability of the chip to handle two independent instructions per cycle. See also core, core duo.

dual diaphragm. A microphone that contains two diaphragms. By electronically combining the two diaphragms in different ways, various polar patterns can be created. Since the polar patterns are created electronically instead of acoustically, in many dual-diaphragm mics, the polar pattern is switchable, either using a switch on the mic or using a remote control on the mic’s power supply. In rare cases, a mic will have two completely different diaphragms—for example, one large diaphragm and one small diaphragm that the user can switch between or use simultaneously.

dual-layer DVD. A DVD containing two layers that can each hold data, allowing nearly double the storage capacity of a standard single-layer DVD. One of the layers is semi-transparent to a great enough extent to allow a laser to focus through it onto the second layer.

dual mono. 1. A two-channel amplifier or processor that maintains complete separation between the two channels, essentially designed and constructed as two separate units inside one case. 2. Using a completely separate monophonic amplifier to drive each of the two speakers in a stereo system. 3. Using two microphones to capture different aspects of a sound source, resulting in two decorrelated signals or tracks. 4. Storing the left and right channels of a stereo audio track in two separate monophonic files on a hard drive.

dub. A copy of a tape.

ducker. A compressor that is set up to reduce the level of a signal or track in response to another signal or track. Typical applications include automatically turning down a background music track during a page or other announcement, dropping the background audio level during a radio commercial so the voiceover can be heard, and so on. A compressor is set up as a ducker by routing the signal that needs to heard—the announcer’s voice, for example—to the sidechain input of the compressor, and the background music to the audio input or inputs on the compressor. When the announcer speaks, the sidechain will trigger the compressor and reduce the level of the background music.

ducking. Using a compressor to automatically turn down a track or signal so that another track or signal can be heard. See ducker.

dummy head. A stereo miking apparatus that uses two microphones mounted in the ears of a fake human head. The idea is to capture the audio as it would be heard by a human listener. The effect is best heard through headphones. See also baffled stereo, binaural.

duty cycle. In synthesis, the amount of time a square or rectangular wave is above zero (positive) versus the amount time it is below zero (negative). A 1:1 duty cycle indicates that the waveform is positive and negative for equal amounts of time. See Figure D.10.

Figure D.10. The duty cycle of square or rectangular wave is how long the wave is positive versus how long it is negative.

DV. Digital video.

DVD. Variously, Digital Versatile Disc, Digital Video Disc, or nothing at all! DVDs are the same physical size as compact discs, but with 4.7 GB of storage capacity for a single-sided, single-layer disc and 8.5 GB for a single-sided dual-layer disc. There are three broad categories: DVD Audio (music), DVD Video (movies), and DVD-ROM (computer software and games). Types and formats of DVDs include:

DVI. Digital Video Interface. A connection standard created by the DDWG (Digital Display Working Group) for displaying analog and digital video on a digital monitor, such as an LCD display. There are three types: DVI-A for analog video, DVI-D for digital video, and DVI-I for both types on a single connector.

DXi. DirectX Instrument. A DirectX-compatible virtual instrument plug-in format for software synthesizers and samplers.

dynamic. A process or characteristic that is constantly changing.

dynamic allocation (a.k.a. voice stealing). All electronic keyboards, synthesizers, and samplers have a finite amount of polyphony—only so many “voices” can be played simultaneously. Dynamic allocation is a system for “stealing” voices when the polyphony of the instrument has been exceeded. Instead of additional notes not sounding when polyphony limits are exceeded, the instrument cuts off an old note and gives that voice to the new note. Usually the oldest note is “stolen,” though there are other schemes, such as stealing the softest note.

dynamic automation. Automation that supports continuous, real-time control over parameters. This allows for smoothly changing fader levels, EQ changes, and other parameter changes over time. See also snapshot automation.

dynamic equalization. An equalizer that responds to level changes in the input signal. Very few hardware equalizers offer dynamic EQ. Some plug-ins offer this feature, though they are more commonly referred to as multiband compressors or limiters. See Figure D.11.

Figure D.11. A multiband compressor is a type of dynamic equalizer that can dynamically change the levels of different frequency bands in response to input levels.

dynamic microphone. A type of microphone in which a thin diaphragm moves in response to sound waves. The diaphragm moves a coil of wire suspended in a magnetic field, creating an electrical signal. Dynamic microphones do not require phantom power. They are generally more durable than other types of mics and can handle high sound pressure levels without distorting, but they may not be as sensitive to high frequencies and transients as some other microphone types are. Dynamic microphones are used live for most applications. In the studio, dynamic microphones are used on electric guitars and basses, drums, some vocals, and other sources.

dynamic range. The ratio (in decibels) of the loudest to the softest signals a system can handle without distortion. In other words, the range of levels a piece of gear is capable of reproducing without distortion. In still other words, the difference between the noise floor and the onset of distortion.

dynamics. 1. Changes in the volume level and intensity of music. 2. Processors that manipulate the dynamics of audio signals, such as compressors, limiters, expanders, de-essers, and duckers.