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Dictionary of Audio Terminology - R


racket - A loud distressing noise.

rack unit - modular unit on which rack panel heights are based. Per the EIA and ANSI standard ANSI/EIA-310-D-1992 Cabinets, Racks, Panels, and Associated Equipment, the modular unit is equal to 44.45 millimeters (1.75"). Panel heights are referred to as "nU" where n is equal to the number of modular units. Examples are 1U (1.75" high), 2U (3.5" high), 3U (5.25" high), etc.

radar (radio detecting and ranging) - (1) A method of detecting distant objects and determining their position, velocity, or other characteristics by analysis of very high frequency radio waves reflected from their surfaces. (2) The equipment used in such detection.

radian - (1) A unit of angular measure equal to the angle subtended at the center of a circle by an arc equal in length to the radius of the circle, approximately 57°17'44.6. (2) - Frequency is measured in radians/second. One cycle (360°) equals 2π (pi) radians.

radiation error - All inclusive term describing the total lobing and cancellation error occurring in a loudspeaker response due to crossover and multiple driver effects.

radio - The wireless transmission through space of electromagnetic waves in the approximate frequency range from 10 kilohertz to 300,000 megahertz.

radio button - A graphical user interface style based on old automobile analog radio designs.

radix - The number base, such as 2 in the binary system and 10 in the decimal system.

radix point - The binary equivalent of the decimal point -- think of it as a "binary point."

Ragone chart - A useful way to compare such things as batteries, this chart plots storage device energy density versus power density on a log-log graph with discharge times represented as diagonal lines.


RAID (Redundant Array of Independent Disks) - A technology providing greater storage functions and reliability using redundancy.

rail-switcher - A term used to describe audio power amplifier designs utilizing more than one power supply for the output, and a means of switching between them based upon the input signal. This scheme improves efficiency.

rail-to-rail® - Registered trademark of Nippon Motorola, Ltd. for their op amp designs having maximum input and output levels equal to the power supply voltages.

rainstick - English translation for the original Chilean instrument called palo de lluvia.

raised cosine filter - A low-pass filter found most often in data communication systems. A perfect raised cosine filter is characterized by a frequency response that is symmetrical about 0 Hz, with a flat low frequency passband, then a smooth rolloff following a cosine curve to zero through the transition region and staying at zero (infinite attenuation) throughout the stopband.

RAM (random access memory) - A memory device in which data may be read out and new data written into any address or location.

Randall, Don - (b. 1917-2008) - American entrepreneur who co-founded Fender in 1946 along with Leo Fender. Beginning in the 1970s he started his own company using the Randall brand.

RaneNotes - A series of technical notes written by Rane's technical staff.

RaneWare® - A registered trademark of Rane Corporation used to identify Rane RW 232 software products.

Rankine scale - A scale of absolute temperature using degrees the same size as those of the Fahrenheit scale, in which the freezing point of water is 491.69° and the boiling point of water is 671.69°.

Rankine, William John Macquorn - (b. 1820-1872), Scottish engineer and physicist.

rarefaction - (1) A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave. (2) The region in which this occurs.

RASTI (room acoustics speech transmission index) - [Originally spelled RaSTI, with lower-case a, which was an acronym for rapid speech transmission index.] A speech intelligibility performance technique developed in 1973 by Dr. Steeneken in Holland, it is simpler than the more complex STI (speech transmission index), however overtime this procedure proved unreliable and was removed as a IEC standard with the 2011 revision to IEC 60268-16.

Rayleigh distance - "The geometric nearfield of a finite acoustic radiator is the area around the radiator where the sound pressure level does not follow spherical or cylindrical spreading ... The Rayleigh distance D = ka²/2, where k = 2 f/c, f is the frequency, c is the sound speed, and a is half the largest dimension, has been used to approximate the size of the geometric nearfield of plane radiators." From Kuntz, Hixson and Ryan, "The Rayleigh distance and geometric nearfield size of nonplane sound radiators," Jour. Acoust. Soc. Amer., Nov., 1983.

Rayleigh, Lord - (b. 1842-1919), Third Baron. Title of John William Strutt. British physicist. He won a 1904 Nobel Prize for investigating the density of gases and for discovering argon with Sir William Ramsay.

R&B (rhythm & blues) - Phrase coined by Jerry Wexler, who would go on to become a famous record producer for Atlantic Records.

RC (room criteria) rating - A new noise criteria adopted by ASHRAE to replace the NC criteria. The RC rating is based on ASHRAE sponsored studies of preference and requirements for speech privacy ratings for "acoustical quality." RC ratings contain both a numerical value and a letter to describe the expected spectral quality of the sound. The numerical part is called the speech interference level (SIL) equal to the arithmetic average of the measured SPL in the 500 Hz, 1 kHz and 2 kHz octave bands, and the letter part denotes the timbre or sound quality as subjectively described by an observer as neutral (N), rumbly (R), hissy (H) or acoustically induced vibration noise (RV). The RC curves serve as optimum spectrum shapes for background sound in buildings. Octave band analysis that meet a specific RC curve are considered neutrally balanced, i.e., they have the desired amounts of low-, mid- and high-frequency content to be heard as not offensive. RC curves are straight lines set at -5 dB/octave slopes (of course -- couldn't be 6, had to be 5). The RC rating standard is Criteria for Evaluating Room Noise, ANSI S12.2.

RCA jack - The Radio Corporation of America (RCA) originally developed this type of unbalanced pin connector for internal chassis connections in radios and televisions during the '30s.

RCDDTM (Registered Communications Distribution Designer) - A designation for individuals who demonstrate expertise in the design, integration, and implementation of telecommunications (voice, data, video, audio, and other low-voltage control) transport systems and their related infrastructure components.

RC time constant - One time constant equals the time required for the output voltage to increase to 63%, or decrease to 37%, of the final value, due to a step input voltage change. This action is fundamentally controlled by a resistor-capacitor pair.

R-DAT or DAT (rotary head digital audio tape recorder) - A digital audio recorder utilizing a magnetic tape cassette system similar to that of a video recorder.

RD-taper - A reversed D-taper.

re - The second tone of the diatonic scale in solfeggio.

REACH (Registration, Evaluation and Authorization of Chemicals) - The EU's latest legislation bans additional chemicals from electronic products.

reactance - The imaginary part of an impedance.

reactive power - The result of multiplying the rms value of the voltage by the rms value of the current in an electronic circuit. It is expressed in watts (W) for resistive loads and in volt-amperes (VA) for reactive loads. It's the amount of power the casual observer thinks is available (hence, apparent), but because of power factor may not be -- the real power is usually less.

Reado - The name of the first FAX machine, introduced by Crosley Radio in 1940.

real power - The total circuit power in watts (resistive load). Contrast with apparent power.

real-time analyzer (RTA) - A constant percentage bandwidth spectrum analyzer.

real-time operation - What is perceived to be instantaneous to a user (or more technically, processing that completes in a specific time allotment).

real-time transport protocol (RTP) - This protocol adds timing and sequence information to Ethernet packets, which allows accurate packet reassembly for real-time audio and video.

Reamp® - Registered trademark by John Cuniberti for his patented reamplifying device first produced in 1994; now owned by Radial Engineering Ltd.

reamplifying - Originally this term meant to take an already recorded guitar sound and use it to drive another different sounding guitar amp -- literally reamplifying it as a means of changing the original recorded sound. Now used on any recorded sound with a real amplifier or virtual plug-in.

rearaxial softspeaker - Term coined by Electro-Voice for their mythical loudspeaker, the SP13.5TRBXWK. Claimed by many to be the speaker that couldn't be made, it might have changed all future loudspeaker design, but it didn't. Characterized by being undirectional, the designer's claimed it produced silken highs and woolen lows. The only loudspeaker known to incorporate both "presence" and "absence" controls. Based on a ridiculously simple principle that still cannot be explained, the SP13.5TRBXWK was only heard once, during the Rane demo of their PI 14 Pseudoacoustic Infector, coupled by a Jensen JE-EP-ERs Multi-denomial Transpedance Informer to a Crown Belchfire BF-6000SUX amplifier.

rebab - A type of bowed or plucked string instrument indigenous to the Middle East.

Recklinghausen, Daniel von - (b. 1925-2011) American engineer and audio inventor who was associated with the AES for over 50 years. Famous for his quote: "If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you've measured the wrong thing."

reconing - The act of replacing a blown, torn, or cracked cone on a dynamic loudspeaker -- a highly skilled operation.

reconstruction filter - A low-pass filter used at the output of digital audio processors (following the DAC) to remove (or at least greatly attenuate) any aliasing products (image spectra present at multiples of the sampling frequency) produced by the use of real-world (non-brickwall) input filters.

Recording Academy, The - The organization formerly known as NARAS.

recording console - At its simplest level, an audio device used to add (combine or sum) multiple inputs into one, two or more outputs, complete with level controls on all inputs.

rectangular coordinates - A coordinate in a rectangular Cartesian coordinate system.

rectifier - An electronic component used to convert from alternating current (AC) to direct-current (DC). Works by only conducting current in one direction which allows inversion or suppression of alternate half cycles.

recursive - A data structure that is defined in terms of itself. For example, in mathematics, an expression, such as a polynomial, each term of which is determined by application of a formula to preceding terms.

Red Book - Nickname for the Philips and Sony's ECMA-130 standard document that defines the format for CD-Audio (compact disc-digital audio) discs; available only to licensees. Compare with Green Book and Yellow Book.

red noise (also called brown noise or Brownian noise) - -6 dB/oct decreasing density (most amount of low frequency energy or power; used in oceanography; power proportional to 1/frequency-squared).

reed relay - A relay using glass-enclosed, magnetically closed reeds as the contact members.

Reed-Solomon code - The most popular and powerful error-correcting code in use.

Reeves, Alec Harley - (b. 1902-1971) British physicist who first proposed PCM (pulse code modulation).

reflection - Sound that is reflected.

reflectors - In acoustics, an object or surface that reflects, or bounces back the original signal. A perfect reflector would reflect with no loss of energy. A diffuser is a special kind of reflector.

refraction - The bending of sound waves caused by entering a medium where the speed of sound is different.

reggae - Popular music of Jamaican origin having elements of calypso and rhythm and blues, characterized by a strongly accentuated offbeat.

reggaeton - A genre of dance music characterized by Entertainment Weekly as "a Spanish-language, pan-American fusion of Stateside hip-hop rhymes, Puerto Rican salsa flourishes, and Jamaican dancehall rhythms." Compare with Jawaiian.

rejustor™ - Trademark of Microbridge Technologies for their family of non-volatile, electrically-adjustable resistors.

REL (Rights Expression Language) - A unified vocabulary for individuals to express copyright law rights.

relay - An electromechanical device with a coil that when energized creates a magnetic field that either opens or closes metal contacts, for making or breaking electrical connections. Invented by Joseph Henry in 1835.

release - How fast the gain is turned back up once the signal drops below the threshold setting. Contrast with attack.

reluctance - A measure of the opposition to magnetic flux, analogous to electric resistance.

remixing - An alternate variation of one or more original song (or video, etc.) compositions created by manipulating the original using various recording techniques to create a new version.

resistance - the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes.

resistivity - Symbol ρ (Greek letter small rho). - An intrinsic property of a material that is measured as its resistance to current per unit length for a uniform cross section.

resistor - Circuit symbol: R (1). An element within a circuit that has specified resistance value designed to restrict the flow of current. (2). A device with the primary purpose of introducing resistance into an electric circuit.

resonance - (1) Electronics. In an LRC circuit, it is the condition where the inductive and capacitive reactances are equal; this is called the resonant frequency. (2) The increase in amplitude of oscillation of an electric or mechanical system exposed to a periodic force whose frequency is equal or very close to the natural undamped frequency of the system.

resonant frequency - the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy.

resonator guitar - Invented by John Dopyera, who founded the Dobro Manufacturing Company with his brothers Rudy, Emile, Robert and Louis, after leaving the National String Instrument Corporation, a company he co-founded.

retro audio - Termed coined by Tomlinson Holman of THX fame, referring to new audio gear designed using legacy or old technology, usually tubes, with cosmetics to match.

return loss - The ratio of the transmitted signal strength to the reflected signal strength. A characteristic often degraded due to excessive bending of the cable.

reverb - Shortened form of reverberator, or reverberation unit. Any electronic or acoustical device designed to simulate, or capture, the natural reverberation of a large hard-surfaced (echoic) room, and mix it back with the original recorded sound. Reverb today is accomplished by digital devices using complex DSP algorithms; previously done using a chamber, a plate, or springs.

reverberation - The total sound field remaining in a room after the original source is silenced. The length of time of this collapsing sound field is called the reverberation time and is defined below. Contrast with echo and ambience.

reverberation time (RT60 and more often today as T30) - all sound remaining after the source stops. The time it takes for this sound to decay is called the reverberation time, and it is quantified by measuring how long it takes the sound pressure level to decay to one-thousanth of its original value. Since one-thousanth equals a 60 dB reduction, reverberation time is abbreviated "RT60," however since most all acousticians measure the decay time for a 30 dB reduction and then doubles the number to express it as RT60, it is more accurately called T30.

reverse mixing - A term coined by Rick Chinn of Uneeda Audio who defines it this way: "Reverse Mixing refers to the practice of listening to a mix and NOT raising the level of something that you can't hear sufficiently but instead looking for the source that is masking what you can't hear and bringing its volume down. This is a good strategy to avoid Climbing Fader Syndrome."

RF (radio frequency) - General term for radio waves.

RFI (radio frequency interference) - A measure of radio frequency (RF) radiation from equipment. An RF disturbance is an electromagnetic disturbance having components in the RF range.

RFID (radio frequency identification) - Technology using RF signals to ID individuals. It uses silicon chip tags with radio frequency functions and on-board memory that holds unique ID numbers, allowing it to ID and track just about anything.

RF-Lite - A low-cost, low-power, two-way, wireless communications standard between compliant devices anywhere in and around the home (automation, toys, PC peripherals, etc.), developed by Philips and others. Claiming lower cost, lower power consumption, higher density of nodes per network and simplicity of protocols, it is an alternative to Bluetooth.

rhythm & blues - Abbr. R&B Phrase coined by Jerry Wexler, who would go on to become a famous record producer for Atlantic Records.

RIAA (Recording Industry Association of America) - A professional trade organization representing the U.S. recording industry. RIAA® members create, manufacture and/or distribute approximately 90% of all sound recordings produced and sold in the United States.

RIAA equalization curve - The standard first proposed by the RIAA and adopted by the disc recording industry in 1953, reaffirmed in 1964 by both the RIAA and NAB and issued as international standard IEC 60098 (old IEC 98) by the IEC, which remains in effect today.

ribbon controller (aka pitch ribbon) - A touch-sensitive strip used to vary pitch. The most popular design is a variable resistor shaped into a linear controller where the resistance is continuously variable from one end to another.

ribbon microphone - Invented in 1923 by Walter Schottky (the same German physicist who invented the famous diode) and Erwin Gerlach of Siemens Halske (German pioneering telegraph company), it is constructed using a very thin metal foil ribbon (~0.002 mm [really] and pleated or corrugated to reduce its longitudinal stiffness, to obtain the lowest resonant frequency so the ribbon is mass-controlled) attached between the poles of a permanent magnet. The acoustic signal (sound pressure variation) causes the ribbon to move and interact with the stationary magnetic field inducing a voltage into the ribbon proportional to the amplitude and frequency of the audio signal.

ribbon tweeter - Invented by Schottky and Gerlach simply by reversing the physical effects of their microphone; it is the inverse of the ribbon microphone described above. It creates a high frequency loudspeaker consisting of a paper-thin metal foil ribbon suspended in a magnetic field (i.e., placed between the poles of a permanent magnet).

Rice, Chester & Kellogg Edward - General Electric researchers who invented and patented the moving-coil direct-radiator loudspeaker in 1924.

Rickenbacker - Name for the company credited with producing the first commercially available electric guitar in 1931 (ten years before Les Paul's innovations).

ring modulator - An effects generator with two inputs and one output. The output is the sum and difference frequencies of the two input signals, and does not contain the original signals -- only the sum and difference signals.

ring out - Shorten form of "ring out a room," slang meaning for locating and treating a sound system's resonant and feedback frequencies.

ring-right-red - Old mantra from the early telephone days meaning the ring of a telephone jack always connects to the right terminal, and is red. Now used by audio designers and installers to remind that the right channel is always the ring in a 1/4" TRS connector and the red RCA phono jack and cable.

ring topology - A network topology where all nodes are daisy chained together (connected) in a closed loop.

RISC (reduced instruction set computer) - A computer design that achieves high performance by doing the most common computer operations very quickly, utilizing a high speed processing technology that uses a far simpler set of operating commands.

ritardando - Gradually slowing in tempo; retarding.

RJ (Registered Jacks) - As in RJ-12 the ubiquitous modular telephone jack, or RJ-45 the connector and wiring used for connecting Ethernet devices.

RLA (Richard Long Associates) - Dance club sound designers during the disco heydays of the '70s and '80s.

RMM (Recreational Music Making) - Music making just for the fun of it.

rms (Root Mean Square) - The square root of the average of the squares of a group of numbers. A useful and more meaningful way of averaging a group of numbers.

roar - Term for noise in the 125 Hz to 500 Hz range.

rock and roll - (seen more often as rock 'n' roll) In 1922, the words "rock" and "roll", which were black slang for sexual intercourse, appear on record for the first time, Trixie Smith's "My Man Rocks Me (With One Steady Roll)".

Rogowski coils - (after Walter Rogowski) A type of current transformer used for measuring alternating current or high-speed current pulses through a conductor.

RoHS (Restriction of Certain Hazardous Substances) - European directive restricting the use of hazardous substances in electrical and electronic equipment.

rolloff rate - The rate at which low-pass, high-pass and bandpass filters attenuate frequencies outside the passband. Expressed in dB/octave, it is a measure of the attenuation slope. Slopes occur in 6 dB/octave increments (due to the natural storage effects of capacitors and inductors), e.g., 12 dB/oct, 18 dB/oct, 24 dB/oct, etc.

ROM (read-only memory) - A memory from which data, after initial storage, may only be read out, but new data cannot be written in. The normal audio CD is an example of a read-only system.

room modes or eigentones - (from German eigen meaning "self" or "own") The acoustic resonances (or standing waves) in a room (or any enclosed space) caused by parallel surfaces. It is the dimensional resonance of a room, where the distance between the walls equals half the wavelength of the lowest resonant frequency (and resonates at all harmonic frequencies above it). Room modes create uneven sound distribution throughout a room, with alternating louder and quieter spots.

room ratios - The ratios of dimensions for a rectanguloid room recommended to ensure a uniform distribution of low frequency room modes.

root mean square - Abbr. rms The square root of the average of the squares of a group of numbers.

rosenfeld - A proposed unit defined as electricity savings of 3 billion kilowatt-hours a year, i.e., equivalent to the amount generated by a 500-megawatt coal-fired plant in one year. After Arthur H. Rosenfeld, who is referred to as the godfather of energy efficiency.

Rosie - First stereo DJ mixer developed by Alex Rosner, named after the designer and for its red paint.

rotary equalizer - A multi-band variable equalizer using rotary controls as the amplitude adjustable elements. Both active and passive designs exist with rotary controls. Center frequency and bandwidth are fixed for each band.

router - An audio device used to selectively assign any input to any output, including the ability to add inputs together. In this way, one input could go to all outputs, or all inputs could go to just one output, or any combination there of.

RPM (Remote Programmable Multiprocessor) - Rane Corporation's trademark for their line of DSP multiprocessor-based digital audio signal processing devices.

RRIO (rail-to-rail input & output) - Term created to indicate op amps with maximum input and output levels equal to the power supply voltages, without violating the registered term rail-to-rail®.

RS (Recommended Standard) - As in RS-232 serial interface standard, et al.

RS-232 - The standard serial interface (EIA/TIA-232-E)used on most personal computers. A format widely supported for bidirectional data transfer at low to moderate rates.

RS-422 - The standard adopted in 1978 by the Electronics Industry Association as EIA-422-A, Electrical characteristics of balanced voltage digital interface circuits. A universal balanced line twisted-pair standard for all long distance (~1000 m, or ~3300 ft) computer interconnections, daisy-chain style.

RS-485 - The standard describing the electrical characteristics of a balanced interface used as a bus for master/slave operation. Allows up to 32 users to bridge onto the line (as opposed to RS-422's need to daisy chain the interconnections).

RS-490 - The standard adopted in 1981 by the EIA entitled Standard Test Methods of Measurement for Audio Amplifiers. The power amp testing standard for consumer products.

RT60 - One-thousanth equals a 60 dB reduction, reverberation time is abbreviated "RT60," however since most all acousticians measure the decay time for a 30 dB reduction and then doubles the number to express it as RT60, it is more accurately called T30.

RTA (real-time analyzer) - A constant percentage bandwidth spectrum analyzer.

RTP (real-time transport protocol) - This protocol adds timing and sequence information to Ethernet packets, which allows accurate packet reassembly for real-time audio and video.

RU (rack unit) - modular unit on which rack panel heights are based. Per the EIA and ANSI standard ANSI/EIA-310-D-1992 Cabinets, Racks, Panels, and Associated Equipment, the modular unit is equal to 44.45 millimeters (1.75"). Panel heights are referred to as "nU" where n is equal to the number of modular units.

ruan - A Chinese four-stringed round lute that dates back to the Qin Dynasty (221 BC - 206 BC).

rubato - Rhythmic flexibility within a phrase or measure; a relaxation of strict time.

rubidium - A soft silvery-white metallic element of the alkali group that ignites spontaneously in air and reacts violently with water, used in photocells and in the manufacture of vacuum tubes. Used in pro audio applications to create the most precise and stable atomic audio clocks for recording studios.

rumble - (1) Term for noise in the 31.5 Hz to 125 Hz range. (2) A quantitative measure of phonograph turntable noise and vibration resulting from performance imperfections.

rumble filter - A high-pass filter used with phonograph turntables to reduce the effects of low frequency noise and vibration, called rumble, caused by imperfections in turntable performance and warped records.

ruthenium - Symbol Ru A hard silver-gray acid-resistant metallic element that is found in platinum ores and is used to harden platinum and palladium for jewelry and in alloys for nonmagnetic wear-resistant instrument pivots and electrical contacts.

RW 232 (also RaneWare) - A trademark of Rane Corporation used to identify Rane's RS-232-based variant of the PA-422 AES standard.

RYTMO (Reaching Youth Through Music Opportunities) - "An after school music program designed to provide a positive, creative and professional environment for underserved youth who demonstrate musical, technical and/or business potential in the arts."





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HistoryOfRecording.com acknowledges the Elsevier, Inc. publication, Audio Engineering know it all, the University of Washington Press publication, The Audio Dictionary, second edition, the Howard W. Sames & Co., Inc. publication, Audio cyclopedia, the Cambridge University Press publication, The Art of Electronics, Rane Corporation (Dennis A. Bohn, CTO), Houghton Mifflin Company publication, The American Heritage Dictionary of the English Language, Fourth Edition, the IEEE publication, IEEE 100: The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition and Wikipedia in the preparation of this Dictionary of Audio Terminology.

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