rack. An enclosure designed to accept rackmountable equipment. A rack may resemble a piece of furniture for studio use, may be a metal cabinet for commercial installations, or may be a portable unit with handles and removable covers. Some racks have wheels to make them more movable when loaded with heavy equipment. Audio racks are set up to accept gear that is 19 inches wide and are measured vertically by the number of rack units of gear they can hold. See also rack space.

rack ear. A bolt-on or integrated flange of metal on the enclosure of a piece of gear that is used to mount the item into a rack.

rackmount. A piece of gear that is physically designed to mount into a standard rack.

rack rail. A wood or metal bar on the inside of a rack that is drilled to accept screws spaced for standard rack spaces.

rack space (a.k.a. rack unit, modular unit). A rack space is a vertical measure of a piece of gear. A single rack space is 1-3/4 inches tall. Equipment can range from a single rack space tall to two, three, four, or even more rack spaces in height.

rack unit. See rack space.

RAID. Redundant Array of Inexpensive Disks (the “official” acronym) or occasionally Redundant Array of Independent Disks. A RAID is a computer storage solution that stores and divides or duplicates data among two or more hard drives that appear as a single drive to the computer. There are two reasons to use a RAID system: faster speed, because the data is being stored to and read from multiple drives (that appear as one drive to the computer), or for back up, as the data is being duplicated on separate drives simultaneously (that appear as one drive to the computer). The disks used can be any plain hard drives; a RAID controller, whether hardware or software, is required to accomplish the RAID functionality. There are several types of RAIDs:

rail. 1. See rack rail. 2. Also known as power supply rail. A metal rod or bar used as a bus to distribute or deliver power from the power supply in some audio devices, such as mixers and amplifiers.

Rainbow Books. A set of books with colored covers developed by Sony/Philips that contains the detailed specifications for a number of different optical compact disc formats.

RAM. Random Access Memory. A type of semiconductor chip that the computer CPU can use to store data for later retrieval. Most types of RAM are volatile and lose their contents when power is removed. There are many types of RAM—some general purpose, and others intended for specific applications. Some examples include:

RAM disk. A computer function that uses part of the machine’s RAM to create a virtual disk drive. RAM disks operate just like physical disk drives, but can access data much faster. However, all data in a RAM disk (and the RAM disk itself) will be lost when the program that created it is shut down or the computer is powered down.

random access. A storage system in which the contents of memory chips or a disk can be accessed or retrieved by jumping directly to an item, rather than stepping linearly or consecutively through the data. Random access is much faster than linear access.

randomize. To produce or arrange data or other items in an unpredictable manner.

random noise. A type of noise often used for making acoustic measurements. Random noise features an even, constantly changing distribution of sound energy across the frequency spectrum. See also pink noise, white noise.

range of human hearing. The range of the highest and lowest frequencies the human ear can perceive. The range of human hearing is generally accepted as 20 Hz to 20,000 Hz, though there are those who feel that we also perceive higher and lower frequencies and that these contribute to the quality of the sound we hear.

rarefaction. An area of decreased air pressure caused by a sound wave. The opposite of a compression.

rate scaling. Rate scaling refers to shortening the length of the envelopes and reducing the volume of the higher notes produced on a synthesizer or sampler. This type of response corresponds more closely to how most acoustic instruments work. See keyboard scaling.

ratio. In a dynamics processor, such as a compressor, limiter, or expander, the ratio is the parameter that defines the amount of level reduction applied when an input signal crosses the threshold. The ratio indicates the change in output level for a given input-level change. For example, with a 2:1 ratio, a 2-dB change in input level results in a 1-dB change in output level (or the output signal having its level change reduced by a factor of 50%); with a 4:1 ratio, a 2-dB change in input level results in a 0.5-dB change in output level (or the output signal having its level change reduced by a factor of 75%). See Figure R.1.

Figure R.1. A dynamics processor’s ratio control determines how much the output level will change compared to the input level.

rattle. See flutter echo.

razorblade. The traditional analog tape editing tool.

RCA plug (a.k.a. phono plug). A type of unbalanced coaxial connector developed by Bell Labs for telephone applications, but widely used by RCA (Radio Corporation of America) for phonograph connections. An RCA plug has a center hot pin surrounded by a ring of ground flanges, which grip the corresponding jack, providing a solid connection. RCA plugs are used on consumer and semi-professional analog audio equipment as well as for S/PDIF digital connections on semi-pro and professional equipment.

R-DAT. Rotating Digital Audio Tape. See DAT.

Real-Audio. A proprietary standard introduced in 1995 by RealNetworks for streaming data-compressed audio over the web. A plug-in decoder is available for most web browsers that support Real-Audio streaming. RealVideo is also available for streaming video content.

real time. Typically, this term is applied to computers and software. Literally, “real time” refers to the computer receiving or reading data, processing it, and outputting it without a perceivable time delay. In audio, “real time” indicates a process or event that happens live and continues while the listener hears it, without breaks or pauses to allow the computer to work.

realtime analyzer (a.k.a. RTA, spectrum analyzer). An audio diagnostic and monitoring device that provides a visual display of the amplitude of the frequency spectrum in real time. A real-time analyzer may be either a hardware device or a computer program or plug-in. RTAs are useful for analyzing rooms, setting up and optimizing audio systems, and assisting with equalization in either live or studio situations.

reamp. A trademarked term of the Reamp Company for the process of playing back a recorded signal through a guitar or other amplifier, then recording the resulting sound to another track. Typically a dry, DI track of the desired guitar performance is recorded during tracking or overdubs. This dry track is then reamped through a variety of different amps in order to try different tones and to arrive at the best sound for the track, all without the player having to perform the part over and over. This allows the engineer greater flexibility and more options for getting the best sound. Note that with DAWs, reamping may mean recording the DI guitar track, then playing back through amplifier simulation plug-ins to achieve the desired sound instead of using a miked-up amplifier. See Figure R.2.

Figure R.2. Reamping allows greater flexibility when deciding on guitar tones. A DI track is recorded, then is sent out through an amplifier and recorded to a new track.

rear-ported. A speaker cabinet or enclosure designed with a port on the rear panel. See also bass reflex.

recap. To replace the capacitors in a piece of gear, such as a mixer or amplifier. Recapping is done to old or vintage gear because some types of capacitors will deteriorate with age, which can affect sound quality. Recapping is also done to “hot-rod” or improve sound quality by replacing the stock capacitors in a unit with higher-grade components.

reconstruction filter. See anti-imaging filter.

record. 1. The process of storing sound in magnetic, analog voltage, digital, or other form. 2. A collection of one or more pieces of music intended for distribution on physical media or via download or streaming. 3. A piece of computer data. 4. A vinyl LP; a plastic disk containing sound stored in grooves.

record arm. See record enable.

record enable. A control or function that “arms” a track or makes it available to record. A track must be record enabled in order to record; this helps prevent the engineer from accidentally recording over tracks that have already been recorded.

recording console (a.k.a. recording desk, recording mixer, mixer, board). A mixing console containing features that are intended and optimized for recording studio applications. Typically, this includes additional inputs for monitoring signals from multitrack tape decks, subgroups, talkback, studio and control room monitor control and switching, and in some cases, automation. See also mixer.

Recording Industry Association of America. See RIAA.

recording session. See session.

record-ready. A track that is armed and ready to record is said to be record-ready.

rectifier. An electronic component that converts AC electricity to DC electricity. Rectifiers are often found in the power supplies for audio equipment and amplifiers. They are most commonly solid state, though tube amplifiers may also use a tube rectifier.

Red Book. One of a set of “Rainbow Books” with colored covers containing the Sony/Philips-developed specifications for different optical compact disc formats. The Red Book contains the specification for audio CD, a.k.a. CD-DA or Compact Disc Digital Audio.

redo. A computer program command that reverses the undo command. Redo restores the data to its condition before the undo command was employed. Many programs now offer unlimited undo, and therefore offer complementary unlimited redo as well. See also undo.

reel. In audio, a “spool” used to wind and store magnetic recording tape. A reel consists of a hub, which is the central axis that the tape is wound around and that mounts to the tape deck, and two flanges, which are the sides of the reel that keep the tape from spilling off.

reel-to-reel. A type of analog or digital tape deck in which the magnetic recording tape is wound and stored on and travels between two open reels, a supply reel and a take-up reel.

reference. 1. To compare the sound quality of two sources. 2. A commercial recording used by an engineer as the basis for sound-quality comparisons.

reference monitor (a.k.a. monitor, studio monitor). A type of speaker optimized to produce flat, uncolored response—this differs from most home stereo, consumer speakers, which are often designed to enhance the sound of music. The idea is for the monitors to deliver true sound to the engineer, so he can depend on them as a reference when making decisions about the sound quality of recordings and mixes. Reference monitors may be either active or passive, and come in a variety of sizes, ranging from models with 3-inch woofers to models with one or more 15-inch woofers. Of course, studio speakers are only part of the monitoring equation; the room, any acoustic treatments, amplifiers driving the speakers, speaker placement, and even cables all affect the sound the engineer hears.

reflect. To bounce off a surface.

Reflection-Free Zone (a.k.a. RFZ^TM). A trademarked term for an area in a studio control room around the main listening position that has been treated with absorbers to reduce or prevent reflections. See Figure R.3.

Figure R.3. A Reflection-Free Zone is an area in a control room where all reflections have been controlled, increasing the accuracy of monitoring. In this case, absorptive acoustic foam has been mounted around the listening position to control reflections.

reflection phase grating. See Schroeder diffusor.

reflector. An acoustical device used to redirect sound waves.

refraction. 1. The “bending” or speed change of a sound wave as it passes from one medium to another or as air-temperature changes occur. 2. The tendency of low-frequency sound waves to bend around objects rather than reflect off of them.

refurbished. 1. A product that did not pass the manufacturer’s quality control and has been remanufactured or repaired. A refurbished product cannot be sold as new—though it may carry a full warranty—and is usually offered at a discount price. 2. A returned product that has been repaired or restored at the factory to meet the manufacturer’s specifications.

regeneration (a.k.a. feedback). A parameter on a delay or other processor that sends a portion of the effected signal back through the processor. In a delay, this results in additional repeats. In a processor such as a flanger, this results in a more intense effect.

region (a.k.a. segment, clip). A term used in some DAWs, sequencers, and audio programs for a segment or piece of audio or MIDI in a track. A region may be a complete audio or MIDI file, or a part of an audio or MIDI file. See Figure R.4.

Figure R.4. Each of the blocks on this track containing a waveform is a separate region of audio.

register. 1. To notify a manufacturer of the identity of a purchaser of a piece of equipment or software in order to receive support, updates, or other bonuses. 2. A small amount of high-speed memory in a CPU. Registers are used to temporarily hold data that will be needed immediately. The CPU transfers necessary data from RAM into a register, operates on it, then returns the data to RAM. 3. One of six vocal ranges or types (bass, baritone, tenor, contralto, soprano, mezzo-soprano). 4. One of three or more pitch ranges of a woodwind instrument, each produced using different blowing techniques. 5. The relative pitch range of a note, melody, instrument, or group of instruments.

registered parameter number (a.k.a. RPN). A continuous controller that is defined or dedicated to a parameter type by the MIDI specification. A registered parameter number is a multi-part message that uses CC #100 and 101 to indicate a parameter number and CC #6 (and optionally 38 for more resolution) to indicate the parameter value. Data increment messages (CC #96 and 97) can be used to adjust the current value of a registered parameter number. There are currently six RPNs: Pitch Bend Range or Sensitivity, Channel Fine Tuning, Channel Coarse Tuning, Tuning Program Select, Tuning Bank Select, and Modulation Depth Range. A seventh RPN, Null, should be sent to cancel access to the RPN after its data has been sent.

relap. To sand and polish a worn tape-recorder head to restore it to its original shape and performance. Relapping can generally only be done once per head; attempting to relap more than once can result in changes in the head gap.

release. 1. In a compressor, the amount of time between when the input signal drops below the threshold and when the unit is no longer applying compression. 2. In a noise gate, the time it takes for the gate to decay to its closed state after the hold stage is complete. Common settings range from two milliseconds to four seconds. 3. In a synthesizer or sampler, the parameter that sets how long a note continues playing after a key has been let up.

release trigger. A sound or sample that is triggered when a note is released. The most common example application of this is with harpsichord sounds. A real harpsichord sounds notes by plucking a string with a small quill or pick when a key is depressed. When the key is released, the quill returns to its ready position, striking the string for a second time as it returns. With a sampled harpsichord, a release trigger can be used to play a sample of the sound of the quill returning past the string when the key is released.

release velocity. How fast a player releases a key on a keyboard—literally, the time it takes for a key to go from the down position to the up position. Release velocity is sent as part of a MIDI note off message and has a range of values from 0 to 127. Release velocity can be routed to control the reverb amount, release time, or any modulation destination that is supported by the receiving device. Despite its expressive possibilities, release velocity is not widely supported by controller keyboards.

remix. 1. A new version of a piece of music created based on one or more tracks from the original multi-track sessions—which may be substantially processed or edited—and additional loops, melodies, harmonies, effects, and accompaniment material. A remix may be as simple as putting the original tracks over new beats or loops, and as complex as creating a completely original new production at an entirely different tempo, built around just the original lead vocal part. 2. To create a new mix of a track.

remote control. 1. A device used to control another device from a distance. A remote can be wired or wireless. Remotes are useful for being able to operate equipment without leaving the studio sweet spot, or for controlling equipment while recording yourself. 2. The ability of a device to respond to commands from another device.

removable storage device. A device that writes data to and reads from cartridges containing hard disks, rewritable CD and DVD media, or cards containing flash memory; or standalone devices, such as USB thumb drives. Removable storage devices provide several advantages: The media is portable and can be placed in any compatible chassis; when a piece of media is full, a new one can be used to expand the amount of storage; adding a new piece of removable media is usually cheaper than purchasing an additional fixed drive; information can be easily backed up to a new piece of media; and so on. The disadvantage is that removable media tend to be slower than fixed media, making removable devices less useful for audio and video playback and editing.

render. To create and write a new audio file based on the processed, mixed, or edited version of the original file.

repro. Short for reproduction, a.k.a. confidence monitoring. A function in some tape recorders that can play back all tracks, including those currently being recorded, using a repro or play head. This allows the engineer to monitor exactly what is being recorded to tape during the session, though there is a very slight delay because of the time it takes for the tape to move from the record head to the repro head.

resampling. A function of some samplers, where the device can play a sample from RAM through internal DSP and effects and re-record the processed output signal as a new sample.

reset. 1. To return a device to its default, power-on state. 2. To return a setting to its previous position.

Reset All Controllers. A MIDI channel message that tells all receiving devices to return all controllers to their default settings.

resistor. An electronic component that opposes or restricts the flow of electrical current by producing a voltage drop. The amount of resistance provided by the component is measured in ohms.

resolution. See bit resolution.

resolve. 1. To exactly synchronize a slave to a master using time code. 2. To synchronize a digital device to an external word or sample clock.

resonance. 1. A parameter on some filters that emphasizes the cutoff frequency. 2. In acoustics, a boost in a particular frequency due to a room mode or standing wave.

resonant. The tendency to vibrate at and reinforce certain frequencies.

resonant filter. A filter with resonance or emphasis at the cutoff frequency. The filter’s Q, or quality factor, determines the bandwidth and sharpness of the resonant peak. In some filters the Q can be increased until the frequencies above and below the cutoff point are no longer heard, and the filter begins to self-oscillate, generating a sine wave tone at the cutoff frequency.

resonant frequency. A frequency at which resonance occurs. Every object and every material has a resonant frequency.

resonant mode. See room mode.

resonator (a.k.a. acoustic resonator). An acoustical device that vibrates sympathetically in response to a sound wave. Because energy at a particular frequency is required to make the resonator vibrate, the energy level at that frequency is reduced in the room. This helps to control room modes and even out the response of the room.

restart (a.k.a. warm boot). A command or process that returns a computer to the state it is in immediately after being powered up, then reloads the operating system. Restarts are often required after installing new software or hardware or updating an application or the operating system. A restart may also be necessary if a device or application locks up or suffers a catastrophic crash.

resultant tone. A sum and/or difference tone that is heard when two loud notes of different pitches are played simultaneously. The sum tone’s frequency equals the sum of the two original notes’ frequencies. (For example, 500-Hz and 100-Hz tones would result in a 600-Hz sum tone.) The difference tone’s frequency equals the difference between the two original notes’ frequencies. (For example, 500-Hz and 100-Hz tones would result in a 400-Hz difference tone.)

resynthesis. The process of analyzing a sound, then using additive or other synthesis techniques to recreate that sound.

retro. An item that imitates an older style.

retrofit. To add a component or option to a device after it leaves the factory.

return. An input connection used to bring a signal back into a mixer after it has been processed using an external device, such as a delay or a reverb. Returns are usually paired with sends to create an external loop into which processors can be inserted.

reverb. See reverberation.

reverberant decay. The time it takes for the reverb in a room to stop ringing. See also RT60.

reverberation. The sound left ringing in a room after the direct sound from the source is silenced. Sometimes mistakenly called echo, reverberation differs in that it is a wash of reflections that typically does not contain discrete, discernible echoes. The reverb quality provides information about the size and shape of the space in which the sound is occurring.

reverb send. A mixer bus or external connection that is dedicated to routing a mix of signals from one or more channels to a reverb processor.

reverb time. A measure of how long reverb lasts in a room. See also RT60.

reverse polarity. A signal or connection whose polarity has been flipped so that positive is negative and vice versa. This is not the same as placing a signal 180 degrees out of phase (though the result can be similar)—changing phase implies a time-based change, whereas polarity is an electrical change.

rewind. A transport control that causes a tape to fast-wind in reverse toward the start of the tape or a DAW or audio program to quickly scroll in reverse toward the beginning of the song or project.

ReWire. An industry-standard protocol for Macintosh and Windows developed jointly by Propeller-head Software and Steinberg, and now supported by most audio software manufacturers. ReWire allows real-time MIDI and audio transfer between different applications running on the same computer. ReWire supports up to 256 audio channels, 4,080 MIDI channels, and transport control between applications.

REX file. A file format developed by Propellerhead Software. A REX file consists of a loop or audio file that has been chopped into slices at attack transients, with each slice assigned to a MIDI note number. The REX file is played back by triggering the slices by playing the appropriate MIDI notes. The speed or tempo of the file can be changed without changing its pitch by triggering the slices at a faster or slower rate. The slices can also be played individually or in a different order by choosing certain notes or varying the order of the MIDI notes used to trigger the slices. Most DAWs support the playback of REX files. REX files can be created from audio files and loops using Propellerhead’s ReCycle or other compatible software.

RFI. Radio Frequency Interference. A type of EMI consisting of radio and television broadcast signals. RFI can be picked up by electronic and audio equipment and cabling, resulting in buzz, hum, and sometimes even the actual broadcast signal mixed in with the desired signal. Shielding, certain types of filters, and proper grounding all help prevent circuits and cables from picking up RFI.

RFZ. See Reflection-Free Zone.

RIAA. Recording Industry Association of America. An organization that works on behalf of the recording industry. The RIAA presents gold and platinum awards for record sales, fights piracy, and has also developed technical standards for LP and copy protection purposes. www.riaa.com.

RIAA equalization (a.k.a. RIAA curve). A standard developed by the RIAA for vinyl LP playback. The RIAA EQ pre-emphasizes the signal during mastering by reducing low frequencies and boosting high frequencies to allow for easier record pressing and duplication. On playback, the reverse curve is applied to the sound to provide the correct sound, with the low frequencies boosted to restore them to their proper level, and the high frequencies reduced —which also reduces hiss from the LP surface.

ribbon cable. A type of wide, flat cable made up of many side-by-side conductors. Ribbon cables are often used inside computers and digital electronic devices because they are easy to route within a confined space and they provide many conductors for signal routing. Because they are unshielded and not very durable, ribbon cables typically are only used for internal connections within a piece of gear, and not for external signal routing, although some external computer peripherals do use ribbon cables for connecting to expansion cards.

ribbon controller. A control device found on some synthesizers consisting of a long, thin conductive strip or ribbon of touch-sensitive material. As a finger is placed on and slid across the ribbon, control messages are generated and can be used to change various parameters, such as pitch, filter cutoff, and others.

ribbon microphone (a.k.a. velocity microphone). A type of microphone that uses a thin corrugated metal ribbon suspended in a magnetic field as a diaphragm. Air motion created by sound waves moves the ribbon, creating a voltage. Ribbon microphones, by nature, have a figure-8 polar pattern. Ribbon microphones tend to be fragile, produce low output, have strong proximity effect, and are sensitive to mic preamp impedance mismatches. (Some modern designs use active circuitry to boost the low levels and to isolate the microphone from the preamp’s impedance.) Ribbon mics are prized by recording engineers for their natural high-frequency response and warm, unhyped sound quality. See also pressure-gradient microphone.

ribbon tweeter. A type of high-frequency driver that uses a very thin ribbon of metal or metal-coated plastic suspended in a magnetic field to create sound waves. A drawback of ribbon tweeters has been their low output, though newer designs have surmounted this problem. Ribbon tweeters tend to have good horizontal dispersion with limited vertical dispersion, making them useful for creating stacked arrays for high-power situations.

riding a fader. Manually adjusting a fader’s level throughout a recording or mixdown pass in order to manage levels without using compression or limiting.

RIFF. Resource Interchange File Format. A multimedia file format developed by Microsoft that serves as a framework for storing multiple types of data, such as audio, video, graphics, MIDI, and other RIFF files in a single package.

ringing out a room. The process of tuning or optimizing a monitor system to control frequency response peaks in the room and system that are prone to feedback. Ringing out a system is done by increasing the volume level until feedback begins, then using an equalizer to reduce the level of the frequency that is feeding back. The level is then increased again until another frequency feeds back; the equalizer is used to pull that frequency down; and so on.

ring modulator. A type of processor that combines two signals and outputs the sum and difference of their frequencies. No original or dry signal is heard at the output. The simplest example is to combine two sine waves—one of 300 Hz and the other at 200 Hz. The sum of the two signals is 500 Hz; the difference is 100 Hz. With complex waveforms, the output from a ring modulator can be extremely complex, often resulting in clangorous “metallic” sounds that have been used as special effects and to create certain types of “robot” voices. See Figure R.5.

Figure R.5. A ring modulator creates new sounds by generating frequencies that are at the sum and difference of the frequencies in two input signals.

RISC. Reduced Instruction Set Computer. A type of CPU developed by IBM in the 1970s that increases speed by very quickly executing simple, uniform, fixed-length instructions, rather than complex instructions. Because the instructions are simpler, RISC allows faster compiling of assembly language or machine code. The Apple Power Mac computers were RISC-based. (“Power” stands for Performance Optimization with Enhanced RISC.)

rise time. The time it takes for a signal or voltage to change from a low value to a high value, typically measured as the time it takes to go from 10% to 90% maximum level. See also transient, transient response.

RJ-45. A type of connector used on Cat 5 and Cat 6 cables for Ethernet and other communication applications.

RMID. RIFF .MID or Resource Interchange File Format .MID. A file format originally developed by Microsoft and adopted by the MMA (MIDI Manufacturers Association) that combines Standard MIDI Files (SMF) with Downloadable Sounds (DLS) and provides a portable way to transfer files while still allowing accurate and consistent playback on any compatible system.

RMS. Root Mean Square. A method used to calculate the average of values over time. In audio, RMS calculations are used to find continuous power ratings. (There is no such thing as “RMS power”; what is usually meant by RMS power is average power. The confusion may come from the fact that RMS voltage and RMS current can be used to calculate average power.)

RoHS. Restriction of Hazardous Substances. An agreement reached in 2006 by members of the European Union to ban new electronic equipment containing amounts of any of six environmentally damaging hazardous substances that exceed specified levels. The substances include lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl, and polybrominated diphenyl. Although RoHS has not been adopted in the United States, many U.S. manufacturers have found it necessary to comply so that their products can be exported to Europe.

rolloff. The gradual reduction in level of frequencies by a filter above or below a cutoff frequency, referred to as a high-frequency rolloff or low-frequency roll-off, respectively. The slope of the rolloff is rated in decibels per octave, with the rolloff slope being steeper with higher numbers. For example, a rolloff of 6 dB per octave would reduce the level 6 dB at a frequency one octave above the cutoff frequency, 12 dB at a frequency two octaves above the cutoff frequency, 18 dB at three octaves above the cutoff, and so on. With a slope of 12 dB per octave, this rate of level reduction would increase twice as fast.

ROM. Read-Only Memory. A type of computer memory chip whose contents can only be read, not modified, erased, or replaced by the user. The contents of ROM chips are sometimes referred to as firmware and typically consist of instructions and data required for the device to operate.

ROMpler. A synthesizer based on sampled waveforms stored in ROM. See also sample-based synthesis.

room mic. A microphone that is positioned some distance from a sound source in order to primarily capture the room ambience and reflections created by the sound of the source. The room mic signal can be blended in with direct mics placed near the source in order to add depth and realism to the sound.

room mode. 1. A low-frequency standing wave in a room. 2. An acoustic resonance at a particular frequency in a room. Room modes occur when sound reflects between parallel surfaces. They cause anomalies in the room’s response that make it very difficult to accurately monitor sound in that room.

room reverb. A type of preset in digital reverbs that attempts to re-create the ambience of a physical space, usually a small to medium-sized room.

room within a room. Type of studio construction in which a floating floor is constructed, then walls and ceiling are built on top of that floor, resulting in a room that is isolated from the surrounding structure.

root directory. In computer file systems, the root directory is the highest-level directory. All the other directories branch off from the root directory.

root key. The note on a keyboard that corresponds to a note being sampled. For example, the note Middle C on a keyboard, to which a sound with the pitch of Middle C will be assigned.

rotary encoder (a.k.a. shaft encoder). A type of control that is turned on a shaft and that resembles a volume knob. Commonly found on control surfaces, a rotary encoder generates MIDI or other data that is used to control parameters in a piece of software or in a hardware device.

rotary speaker. A speaker cabinet in which the driver rotates, or a horn or baffle rotates around the driver. A unique chorusing effect is created in a rotating speaker because of the Doppler Effect; as the driver rotates away from and toward the listener, the pitch of the sound it is producing changes. The most recognizable example of a rotating speaker is the Leslie speaker (actually a family of models), which was invented by Donald Leslie and first produced in 1941. The original Leslie cabinet was designed to be used with Hammond organs, though rotating speakers from several manufacturers are compatible with other instruments, such as electric guitar.

rotational delay. The time it takes for a specific area or location on a hard drive or optical disc to rotate under the read/write head. Rotational delay, together with seek time and transfer time, determines a drive’s access time.

rough mix. A quick mix created for the purposes of evaluating a song, mix ideas, an arrangement, processing, or for other reasons. A rough mix may also be used as a guide for overdubbing additional parts. A rough mix is not intended for release to the public, but is a reference for the project’s producer, engineer, and musicians.

RPM. Revolutions Per Minute. The number of times a disk or other item that spins around an axis rotates in a minute. This is an important spec for hard drives; the faster the disc revolves, the shorter the time the read or write head has to wait to reach a specific location or piece of data.

RPN. See registered parameter number.

RS-232. Recommended Standard 232. A telecommunication protocol developed in 1969 by the EIA (Electronics Industry Association) and commonly used for personal computer serial ports. RS-232 is intended for short- to medium-distance (up to 15 meters) serial bidirectional data transmission and uses DB-25 or other multi-pin connectors.

RS-422. Recommended Standard 422. A balanced telecommunication protocol developed in 1978 by the EIA (Electronics Industry Association). RS-422 is used for long-distance serial data transmission over twisted-pair balanced lines.

RTA. See real-time analyzer.

RTAS. Real-Time AudioSuite. A real-time native plug-in format developed by Digidesign for use in DAE-compatible host audio software, such as Pro Tools HD, Pro Tools LE, Pro Tools M-Powered, and MOTU Digital Performer. The RTAS format supports both processing and virtual instrument plug-ins.

RT60. Abbreviation for Reverb Time-60 dB. The time it takes for the reverberation in a room to drop in level by 60 decibels.

RTZ. Return To Zero. A transport control that rewinds a recording to the zero point on a time or location counter.

rumble. Low-frequency noise, typically below 50 Hz, often caused by mechanical sources such as traffic, HVAC systems, or trains, or by a playback/recording transport, such as a turntable. In many cases, rumble can be removed using a high-pass filter.