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Dictionary of Audio Terminology - S

SAA (semantic audio analysis) - The automatic extraction of meaning from audio and the means for representing it, typically as metadata.

sabin - A non-metric unit of sound absorption used in acoustical engineering. One sabin is the sound absorption of one square foot (or one square meter -- a metric sabin) of a perfectly absorbing surface--such as an open window. The sound absorption of a wall or some other surface is the area of the surface, in square feet, multiplied by a coefficient that depends on the material of the surface and on the frequency of the sound. These coefficients are carefully measured and tabulated. The unit honors Wallace Sabine. Sabine used this unit, which he called the open window unit (owu), as early as 1911.

Sabine, Wallace Clement Ware - (b.1868-1919) American physicist and Harvard University professor who founded the systematic study of acoustics around 1895. Regarded as the father of the science of architectural acoustics.

SAC (sound absorption coefficient) - property of any material that changes the acoustic energy of sound waves into another form, often heat, which it to some extent retains, as opposed to that sound energy that material reflects or conducts.

SACD® (Super Audio CD®) - Also known as DSD® or Direct Stream Digital®, joint trademark of Sony and Philips for their proposal for the next generation CD-standard. Sony and Philips have split from the DVD ranks to jointly propose their own solution comprised of a 1-bit, 64-times oversampled direct-stream digital SACD format. The original SACD proposal was for a hybrid disc comprising two layers: a high density (HD) DSD layer in the middle, and a standard density CD layer at the bottom. The two layers are read from the same side of the disc; the CD laser reads the bottom reflective layer through the semi-transmissive HD layer, while the middle layer is read by the HD laser delivering high-quality, multichannel sound without sacrificing backward compatibility. The HD layer has three tracks: the innermost is for two-channel stereo; the middle is a six-channel mix; and the outer is for such additional information as liner notes, still images and video clips. Maximum playing time is 74 minutes. This proposal turned out to be too expensive, so the SACD first release is a single-layer SACD-only disc.

SAE (Society of Automotive Engineers) - The international trade organization comprised of 80,000 engineers, business executives, educators, and students representing 100 countries that functions as the resource for technical information and expertise used in designing, building, maintaining, and operating self-propelled vehicles for use on land or sea, in air or space.

SAMPA (speech assessment methods phonetic alphabet) - A computer-readable phonetic script using 7-bit printable ASCII characters based on the IPA.

sample rate conversion - The process of converting one sample rate to another, e.g. 44.1 kHz to 48 kHz. Necessary for the communication and synchronization of dissimilar digital audio devices, e.g., digital tape machines to CD mastering machines.

sample-and-hold (S/H) - A circuit that captures and holds an analog signal for a finite period. The input S/H proceeds the A/D converter, allowing time for conversion. The output S/H follows the D/A converter, smoothing glitches.

Sampling (Nyquist) Theorem - A theorem stating that a bandlimited continuous waveform may be represented by a series of discrete samples if the sampling frequency is at least twice the highest frequency contained in the waveform.

sampling frequency or sampling rate - The frequency or rate at which an analog signal is sampled or converted into digital data. Expressed in Hertz (cycles per second). For example, compact disc sampling rate is 44,100 samples per second or 44.1 kHz, however in pro audio other rates exist: common examples being 32 kHz, 48 kHz, and 50 kHz.

sampling - The process of representing the amplitude of a signal at a particular point in time.

SAN (storage area network) - A network connecting host computers to storage servers and systems. SAN technology allows high-speed connection of multiple workstations to a centralized hard-disk network (via fiber optics interconnection), allowing each workstation to access any drive from any location (e.g., control rooms in DAW recording studios).

SAR (successive approximation register) - A type of analog-to-digital converter using a digital-to-analog converter to determine the output word successively, bit by bit.

saser (sound amplification by stimulated emission of radiation) - The ultrasonic acoustic version of a laser operating in the megahertz to terahertz range.

SAVVI (Sound, Audio Visual, and Video Integrators Council) - One of ICIA's councils that focuses on the needs and interests of companies that install and integrate AV systems, and seeks to identify best practices.

sawtooth wave - A periodic waveform characterized by a 50% duty cycle and a Fourier series consisting of both even- and odd-ordered, equal phase, sinusoidal harmonic components of its fundamental frequency. The amplitudes (coefficients multiplying the magnitude of the fundamental sine wave) of the odd-ordered harmonics are the same as a square wave, while the amplitudes (re the fundamental) for the even-ordered harmonics are -1/n, where n is the even harmonic number. Therefore the first few even harmonic multipliers are -1/2, -1/4, -1/6, ... etc., and the first few odd harmonic multipliers are 1/3, 1/5, 1/7, ... etc.

Sax, Adolphe - (b. 1814-1894) Belgian musical instrument designer and inventor of the saxophone.

SBR (spectral band replication) - An audio coding technology invented by Coding Technologies.

Schmitt, Otto Herbert - (b. 1913-1998) American scientist most noted for his inventing the Schmitt trigger, the differential amplifier and the cathode-coupled amplifier.

Schmitt trigger - A solid state element that produces an output when the input exceeds a specified turn-on level, and whose output continues until the input falls below a specified turn-off level. The on and off levels have different values, making this a comparator with hysteresis. Invented by Otto Herbert Schmitt in 1934 while still a graduate student, he named it a "thermionic trigger" and didn't get it written up until he published it in 1938.

Schottky, Walter - (b. 1886-1976) German physicist whose work in solid-state physics and electronics resulted in many inventions that bear his name (Schottky effect, Schottky barrier, Schottky diode). He also invented the tetrode and (with Erwin Gerlach) the ribbon microphone and ribbon tweeter.

Schottky noise - Noise voltage developed in a thermionic tube because of the random variations in the number and the velocity of electrons emitted by the heated cathode; the effect causes sputtering or popping sounds in radio receivers and snow effects in analog television pictures.

Schroeder diffuser - A Schroeder diffuser is a structure comprising a number of wells of different, carefully chosen depths. As a soundwave strikes the irregular surface, instead of bouncing off it like a mirror, it bounces out of each well at a slightly different time.

Schroeder, Manfred R. - (b. 1926-2009) German physicist best known in the pro audio world for inventing the acoustic diffuser.

SCIN (shield current induced noise) - The term coined by Neil Muncy in 1994 to describe the non-uniform magnetic coupling of shield current in balanced audio cables to the two signal conductors.

SCMS (serial copy management system) - The copy protection scheme applied to consumer digital recording equipment -- it does not apply to professional machines. This standard allows unlimited analog-to-digital copies, but only one digital-to-digital copy. This is done by two control bits (the C and L bits) contained within the digital audio data.

SCR (silicon controlled rectifier) - a four-layer solid state device that controls current. The name "silicon controlled rectifier" or SCR is General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Gordon Hall and commercialized by Frank W. "Bill" Gutzwiller in 1957.

scrap flutter - (also called frequency-modulation (friction) noise) - Frequency modulation of the signal in the range above approximately 100 Hz resulting in distortion which may be perceived as a noise added to the signal (that is, a noise not present in the absence of a signal).

scratching - A turntablist technique originated by Grand Wizzard Theodore developed from Grandmaster Flash.

screen - Alternate term used to mean the same as shield.

SCSI port (small computer system interface) - A standard 8-bit parallel interface used to connect up to seven peripherals, such as connecting a CD-ROM player or document scanner to a microcomputer.

SD (super density compact disc) - One was the Multimedia Compact Disc (MMCD), supported by Toshiba, Time Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC.

SDDS® (Sony Dynamic Digital Sound) - Sony's competing format for the digital soundtrack system for motion picture playback. The signal is optically printed outside the sprocket holes, along both sides of the print.

SDIF (Sony digital interface format) - Sony's professional digital audio interface utilizing two BNC-type connectors, one for each audio channel, and a separate BNC-type connector for word synchronization, common to both channels. All interconnection is done using unbalanced 75 ohm coaxial cable of the exact same length (to preserve synchronization), and is not intended for long distances.

SDK (software development kit) - A programming set-of-rules that enables development of applications for existing program families or platforms.

SDMI (Secure Digital Music Initiative) - A multi-industry group defining a specification to protect digital music distribution.

s-domain - The Laplace domain for continuous time systems. Contrast with Z-domain.

second - Abbr. s also sec - A unit of time equal to one sixtieth of an minute (time). Technically defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.

second (plane angle) Abbr. " A unit of angular measurement equal to one sixtieth of a minute (plane angle).

second-order filter - An electronic filter described by a transfer function having quadratic equations in the numerator and denominator.

SED (Surface-conduction Electron-emitting Display) - Video display technology. Proprietary flat-panel, high-resolution display technology jointly developed by Canon and Toshiba, characterized by low power consumption and a very high quality image comparable to CRT.

segue - To make a transition directly from one section or theme to another.

seismic noise - Small vibrations usually thought of as noise are now being used to gather new information about the Earth's crust. Examples include ocean waves crashing on the beach and storms passing by causing small changes in air pressure.

self-noise - Residual noise, or the inherent noise level of a microphone when no signal is present. Microphone inherent self-noise is usually specified as the equivalent SPL level which would give the same output voltage, with typical values being 15-20 dB SPL.

Sel-Sync™ (Selective Synchronous) - Ampex trademark for their revolutionary 8-track recorder developed in 1955 for Les Paul by Ampex engineer Mort Fujii. Interestingly, upon advice of their attorney, Ampex did not apply for a patent.

semitone - An interval equal to a half tone in the standard diatonic scale. Also called half-step, half-tone.

Sennheiser, Fritz - (b. 1912-2010) German PhD engineer who founded Sennheiser in the late '40s, in post-war Germany.

sensitivity - (1) The standard way to rate audio devices like microphones, headphones and loudspeakers. A standard input value is applied and the resultant output is measured and stated.

· loudspeaker sensitivity The standard is to apply one watt and measure the sound pressure level (SPL) at a distance of one meter. [IEC 60268-5]
· headphone sensitivity The standard is to apply one milliwatt and then measure the sound pressure level at the earpiece (using a dummy head with built-in microphones). [IEC 60268-7]
· microphone sensitivity The standard is to apply a 1 kHz sound source equal to 94 dB- SPL (one pascal) and then measure the output level and express it in mV/PA (millivolts per pascal). [IEC 60268-4]

(2) The minimum input signal required to produce a standard output level.

· power amplifier sensitivity The input level required to produce one watt output into a specified load impedance, usually 4 or 8 ohms. [EIA-490]
· radio receiver sensitivity The input level required to produce a specified signal-to-noise ratio.

separation mastering - A specific group of tracks used in mastering, e.g., drums, bass, vocals, etc. Compare with stems, which are individual tracks instead of a group of tracks.

serial interface - A connection which allows transmission of only one bit at a time. An example in the PC world is a RS-232 port, primarily used for modems and mice. A serial interface transmits each bit in a word in sequence over one communication link. See also parallel interface.

serializer - A parallel-to-serial data converter; used in buses and networks.

series circuit - The connection of components such that the same current passes through each device in completing its path to the source of supply. For example series connection of a battery is made by connecting the positive terminal of each successive cell to the negative terminal of the next adjacent cell so that their voltage are additive.

series-mode surge suppression - Operates by storing the surge energy in a resonant circuit and slowly discharging it back into the power line. Claimed to overcome shunt-mode surge suppression shortcomings, specifically those of finite lifetimes, degrading with time and coupling noise into the ground system.

server - A shared master computer on a local area network (LAN) used to store files and distribute them to clients upon demand.

servo-loop; servo-locked loop; servo-mechanism - A self-regulating feedback system or mechanism. Typically a feedback system consisting of a sensing element, an amplifier, and a (servo)motor, used in the automatic control of a mechanical device (such as a loudspeaker). In audio, usually the name applies to a class of electronic control circuits comprised of an amplifier and a feedback path from the output signal that is compared with a reference signal. This topology creates an error signal that is the difference between the reference and the output signal. The error signal causes the output to do whatever is necessary to reduce the error to zero. A loudspeaker system with motional feedback is such a system. A sensor is attached to the speaker cone and provides a feedback signal that is compared against the driving signal to create more accurate control of the loudspeaker. Another example is Rane's servo-locked limiter™ which is an audio peak limiter circuit where the output is compared against a reference signal (the threshold setting) creating an error signal that reduces the gain of the circuit until the error is zero.

servo-locked limiter™ - Rane Corporation trademark for their proprietary limiter circuit.

SFDR (spurious free dynamic range) - A testing method used in quantifying high-speed data converters and high-frequency communication integrated circuits. It is the difference in dB between the desired output signal and any undesired harmonics found in the output spectrum.

SFG (Shepard function generator) - A circuit that produces a continuously ascending or descending tone. Named after American psychologist Roger Newland Shepard, who wrote a paper in 1964 describing his cognitive experiments using this technique ["Circularity in Judgments of Relative Pitch," J. Acous. Soc., vol. 36, no. 12, 1964, pp. 2346-2353].

Shannon, Claude E. (b. 1916-2001) American mathematician and physicist who is credited as the father of information theory (For the mathematically advanced, see his famous paper, "A Mathematical Theory of Communication" published in 1948 in The Bell).

shaped triangular - See or high-passed triangular probability density function, which is essentially high-pass filtered triangular dither that places most of the dither energy at higher frequencies making it less audible.

Shearer Horn - After inventor Douglas Shearer, a huge two-way system that marked the beginning of modern sound systems and found instant fame in motion picture theaters. It received a technical Academy Award in 1936.

sheath - The insulating layer of material that surrounds a wire or cable offering protection.

shelving response - Term used to describe a flat (or shelf) end-band shape when applied to program equalization. Also known as bass and treble tone control responses.

Shepard function generator - (aka barberpole tone, also Shepard's tone) - A circuit that produces a continuously ascending or descending tone. Named after American psychologist Roger Newland Shepard, who wrote a paper in 1964 describing his cognitive experiments using this technique ["Circularity in Judgments of Relative Pitch," J. Acous. Soc., vol. 36, no. 12, 1964, pp. 2346-2353].

SHF (super high frequency) - 3 GHz to 30 GHz.

shield - (1) A structure or arrangement of metal plates or mesh designed to protect a piece of electronic equipment from electrostatic or magnetic interference. (2) As normally applied to instrumentation cables, refers to the metallic sheath (usually copper or aluminum), applied over the insulation of a conductor or conductors for the purpose of providing means for reducing electrostatic coupling between the conductors so shielded and others which may be susceptible to or which may be generating unwanted (noise) electrostatic fields.

short circuit - The condition where two or more nodes are directly connected together, resulting in zero voltage between the nodes.

shotgun microphone - The most directional response pattern, characterized by small sensitivity lobes on the left, right, and rear, with extreme sensitivity to the front.

shot noise - Noise caused by current fluctuations due to the discrete nature of charge carriers and random or unpredictable (or both) nature of charged particles from an emitter.

ShotSpotter® - Leaders in gunshot and explosion detection and location.

show control - A term originally created by Charlie Richmond (Richmond Sound Design) to describe a new form of MIDI control designed for live theater venues. His efforts resulted in the official MIDI Show Control (MSC) specification. This document states: "The purpose of MIDI Show Control is to allow MIDI systems to communicate with and to control dedicated intelligent control equipment in theatrical, live performance, multi-media, audio-visual and similar environments."

shunt-mode surge suppression - Technology which shorts surge currents to ground using MOVs and other TVS devices.

SI (International System of Units) - The International System of Units, universally abbreviated SI (from the French Le Système International d'Unités), is the modern metric system of measurement. SI is the dominant measurement system not only in science, but also in international commerce.

SIAP (System for Improved Acoustic Performance) - An EAE system developed by this Netherlands company.

sibilant - Of, characterized by, or producing a hissing sound like that of (s) or (sh): the sibilant consonants; a sibilant bird call. A sibilant speech sound, such as English (s), (sh), (z), or (zh).

SID (slew-induced distortion) - caused when an amplifier or transducer is required to change output (or displacement), i.e. slew, faster than it is able to do so without error. At such times any other signals may suffer considerable gain distortion, leading to Intermodulation distortion. Transient Intermodulation Distortion may involve some degree of SID and/or distortion due to peak compression.

side-chain - In a signal processing circuit, such as one employing a VCA, a secondary signal path in parallel with the main signal path in which the condition or parameter of an audio signal that will cause a processor to begin working is sensed or detected. Typical applications use the side-chain information to control the gain of a VCA. The circuit may detect level or frequency or both. Devices utilizing side-chains for control generally fall into the classification of dynamic controllers.

sidetone - The feature of a telephone handset that allows you to hear yourself talk, acting as feedback that the phone is really working. Sidetones are actually short line echoes bled back into the earpiece. Too much sidetone sounds like an echo and too little sounds so quiet that people think the phone is broken. Sidetones are good for people but can cause acoustic feedback in teleconferencing systems if not treated properly.

siemens Abbr. S - A unit of electrical conductance in the International System, equal to one ampere per volt. [After Siemens, Ernst Werner von.]

Siemens, Ernst Werner von - (b. 1816-1892) German engineer who made notable improvements to telegraphic and electrical apparatus, and founded the company, Siemens. He patented the first loudspeaker in 1877.

sigma-delta (Δ-Σ) - An analog-to-digital conversion scheme rooted in a design originally proposed in 1946, but not made practical until 1974 by James C. Candy. Inose and Yasuda coined the name delta-sigma modulation at the University of Tokyo in 1962, but due to a misunderstanding the words were interchanged and taken to be sigma-delta. Both names are still used for describing this modulator. Characterized by oversampling and digital filtering to achieve high performance at low cost, a delta-sigma A/D thus consists of an analog modulator and a digital filter. The fundamental principle behind the modulator is that of a single-bit A/D converter embedded in an analog negative feedback loop with high open loop gain. The modulator loop oversamples and processes the analog input at a rate much higher than the bandwidth of interest (see: Sampling (Nyquist) Theorem). The modulator's output provides 1-bit information at a very high rate and in a format that a digital filter can process to extract higher resolution (such as 20-bits) at a lower rate.

signal ground - The common electrical reference point of a circuit, usually separate from the chassis ground but tied together at the power supply.

signal levels - Terms used to describe relative audio signal levels:

mic-level Nominal signal coming directly from a microphone. Very low, in the microvolts, and requires a preamp with at least 60 dB gain before using with any line-level equipment.

line-level Standard +4 dBu or -10 dBV audio levels.

instrument-level Nominal signal from musical instruments using electrical pick-ups. Varies widely, from very low mic-levels to quite large line-levels.

signal present indicator or SIG PRES An indicator found on pro audio signal processing units that lights once the input signal level exceeds a preset point. There is no standard specifying when a SIG PRES light should illuminate, although common practice makes it -20 dBu (77.5 mV), or the pro audio de facto standard line-level of +4 dBu (1.23 volts).

signal-to-noise ratio - An audio measurement of the residual noise of a unit, stated as the ratio of signal level (or power) to noise level (or power), normally expressed in decibels. The "signal" reference level must be stated. Typically this is either the expected nominal operating level, say, +4 dBu for professional audio, or the maximum output level, usually around +20 dBu. The noise is measured using a true rms type voltmeter over a specified bandwidth, and sometimes using weighting filters. All these thing must be stated for a S/N spec to have meaning. Simply saying a unit has a SNR of 90 dB means nothing, without giving the reference level, measurement bandwidth, and any weighting filers. A system's maximum S/N is called the dynamic range.

SIL (speech interference level) - The numerical part of the RC noise rating.

Silicon Dust™ - Nickname for microchips. Trademarked name first coined by National Semiconductor to describe the world's smallest op amp (as of May 5, 1999), the LMV921. Used in surface mount technology (SMT), they are about the size of a single letter on this page.

silver - One of the English language words without a rhyme -- others are "month," "orange" & "purple."

simplex power Old telephone term for phantom power.

SIN (signal induced noise) - Tongue-in-cheek term created by John K. Chester for cable shield induced noise found when the analog audio cable shield is grounded at one end only.

SINAD (pronounced "sin-add") or S/N+D (signal-to-noise and distortion) Acronym for the ratio: (signal + noise + distortion) / (noise + distortion).

sinc function - The unnormalized definition is sin (x)/x; normalizing adds pi to each x-term. In pro audio it is used in aliasing to design sinc filters.

sine Abbr. sin - (1) The ordinate of the endpoint of an arc of a unit circle centered at the origin of a Cartesian coordinate system, the arc being of length x and measured counterclockwise from the point (1, 0) if x is positive or clockwise if x is negative. (2) In a right triangle, the ratio of the length of the side opposite an acute angle to the length of the hypotenuse.

sine curve - The graph of the equation y = sin x. Also called sinusoid.

sine wave - A waveform with deviation that can be graphically expressed as the sine curve.

sine wave speech - A term coined by psychologists Robert Remez and David Pisoni to describe their experiment consisting of synthesizing three simultaneous wavering sine wave tones. The sound was nothing like speech, yet participants could hear words thus suggesting that the brain can hear speech content in sounds that do not even resemble speech.

sinusoid - The graph of the equation y = sin x.

sitar A stringed instrument of India made of seasoned gourds and teak and having a track of 20 movable frets with 6 or 7 metal playing strings above and usually 13 sympathetic resonating strings below.

Six Sigma Abbr. 6s and 6 Sigma - In 1986, Bill Smith, a senior engineer and scientist at Motorola, introduced the concept of Six Sigma (a registered trademark of Motorola, Inc.) to standardize the way defects are counted. Simply put, it is a statistical methodology for improving quality control. The Greek letter "sigma" is used in statistics to represent one standard deviation. This measures how far a given process deviates from perfection. Six sigma refers to six standard deviations, which equals 99.99985% of the total (1.5 defects per million). The central idea behind Six Sigma is that if you can measure how many defects you have in a process, you can systematically figure out how to eliminate them and get as close to zero defects as possible. However, today six sigma methods foster a huge business in and of itself.

skin effect - (1) The tendency of high frequency (RF and higher) current to be concentrated at the surface of the conductor.

slap echo also called slapback - (1) A single echo resulting from parallel non-absorbing (i.e., reflective) walls, characterized by lots of high frequency content. So-called because you can test for slap echo by sharply clapping your hands and listening for the characteristic sound of the echo in the mid-range. Slap echo smears a stereo sound field by destroying the critical phase relationships necessary to form an accurate sound stage. (2) Devices that simulate slap echo are popular in recording. One distinct repeat echo is added to an instrument sound resulting in a very live sound similar to what you would hear in an auditorium.

slew rate - (1) The term used to define the maximum rate of change of an amplifier's output voltage with respect to its input voltage. In essence, slew rate is a measure of an amplifier's ability to follow its input signal. It is measured by applying a large amplitude step function (a signal starting at 0 volts and "instantaneously" jumping to some large level [without overshoot or ringing], creating a step-like look on an oscilloscope) to the amplifier under test and measuring the slope of the output waveform. For a "perfect" step input (i.e., one with a rise time at least 100 times faster than the amplifier under test), the output will not be vertical; it will exhibit a pronounced slope. The slope is caused by the amplifier having a finite amount of current available to charge and discharge its internal compensation capacitor. (2) Slew rate is defined to be the maximum derivative of the output voltage with respect to time. That is, it is a measure of the worst case delta change of voltage over a delta change in time, or the rate-of-change of the voltage vs. time. For sinusoidal signals (audio), this equals 2 pi times the maximum frequency, times the maximum peak output voltage: SR = (2 pi) (Fmax) (Vpeak).

SLS (scalable lossless coding) - Popular name for the MPEG-4 standard, ISO/IEC 14496-3, for lossless audio coding. This technology combines lossy audio coding, lossless audio coding and scalable audio coding in a single framework.

smoke - From the phlogiston theory of electronics, it is smoke that makes ICs and transistors work. The proof of this is self-evident because every time you let the smoke out of an IC or transistor it stops working -- elementary. This has been verified through exhaustive testing, particularly regarding power amplifier ICs and transistors. (Incidentally, wires carry smoke from one device to another.) [Origin unknown but classic.]

smoothing filter - The Savitzky–Golay method essentially performs a local polynomial regression (of degree k) on a series of values (of at least k+1 points which are treated as being equally spaced in the series) to determine the smoothed value for each point. Methods are also provided for calculating the first up to the fifth derivatives.

SMPS (switch-mode, or switchmode, power supply) - An electronic power supply characterized by switching a power transistor on and off with a variable duty cycle whose average is the desired output voltage.

SMPTE (pronounced "simty") (Society of Motion Picture and Television Engineers) A professional engineering society that establishes standards, including a time code standard used for synchronization.

SMT (surface mounting technology) - The science of attaching and interconnecting electronic devices, whose entire body projects in front of the mounting surface, as opposed to through-hole devices found on the earliest printed circuit boards. With surface mount technology all components sit on the surface of printed circuit boards and are soldered to conductive pads. With through-hole parts, component leads are placed through holes in the boards and then soldered from the back side. SMT is more cost-effective and allows far greater density of parts.

S/MUX - (1) Sample Multiplexing. Proprietary technology licensed by Sonorus used to transmit high bandwidth digital audio using existing lower bandwidth technology. (2) Serial Multiplexer manufactured by MicroRidge. (3) Subtitle Multiplexer manufactured by Cavena.

S/N or SNR (signal-to-noise ratio) An audio measurement of the residual noise of a unit, stated as the ratio of signal level (or power) to noise level (or power), normally expressed in decibels. The "signal" reference level must be stated. Typically this is either the expected nominal operating level, say, +4 dBu for professional audio, or the maximum output level, usually around +20 dBu. The noise is measured using a true rms type voltmeter over a specified bandwidth, and sometimes using weighting filters. All these thing must be stated for a S/N spec to have meaning. Simply saying a unit has a SNR of 90 dB means nothing, without giving the reference level, measurement bandwidth, and any weighting filers. A system's maximum S/N is called the dynamic range.

snake or audio snake - The nickname for the cable running from the stage of a live performance to the main mixing console, which is usually set-up in the middle or rear of the audience (in spite of being called FOH). It typically contains one shielded pair (STP) of wires for each of the stage microphones. The name comes from the multiconductor cable looking sort of snake-like.

snapshot - A term coined by British hunters to describe a quick shot with a gun. First applied to cameras at the Chicago World's Fair in 1893 where Kodak rented and popularized the first point-and-shoot camera. So called because the photographs taken were fast.

S/N+D or S/(N+D) (signal-to-noise and distortion) - Acronym for the ratio: (signal + noise + distortion) / (noise + distortion).

Snell's Law - States the relationship between the angles of incidence and refraction and the indices of refraction of any two mediums.

SNMP (Simple Network Management Protocol) - The most common method by which network management applications can query a management agent using a supported MIB (Management Information Base). SNMP operates at the OSI Application layer. The IP (Internet Protocol)-based SNMP is the basis of most network management software, to the extent that today the phrase "managed device" implies SNMP compliance.

Snow, William B. - (b. 1903-1968) American engineer best remembered for his foundation work for stereophonic reproduction in large rooms. See U.S. Patent 2,137,032 Sound Reproducing System. His paper titled "Basic Principles of Stereophonic Sound," Stereophonic Techniques: An Anthology, edited by John Eargle (Audio Engineering Society, ISBN 0-937803-08-1, NY, 1986, pp. 9-31) is considered the best introduction to this subject. Other papers of interest by Snow are collected in Sound Reinforcement: An Anthology, edited by David L. Klepper (Audio Engineering Society, NY, 1978).

SNS (sudden noise syndrome) - Term coined by Karl Brunvoll of Renkus-Heinz to describe high-level intermittent noise (oscillaiton).

sodar (sonic detection and ranging) - "A meteorological instrument also known as a wind profiler which measures the scattering of sound waves by atmospheric turbulence." From link. Compare with sonar and radar.

soft clipping - moderate clipping that results in waveforms having softly-rounded edges, as opposed to the sharp edges of hard clipping.

software driver The final software interface between high-level programs and the driven hardware.

sol - The fifth tone of the diatonic scale in solfeggio.

sol-fa - The set of syllables do, re, mi, fa, sol, la, and ti, used to represent the tones of the scale.

solfeggio - (1). Use of the sol-fa syllables to note the tones of the scale; solmization. (2) A singing exercise in which the sol-fa syllables are used instead of text.

solo - A term used in recording and live-sound mixing to describe monitoring (via headphones) a single channel without affecting the main outputs (see PFL) -- same as cueing; however, it can also refer to certain console designs where it replaces the main mix with the soloed channel (called destructive solo).

sonar (sound navigation and ranging) - (1) A system using transmitted and reflected underwater sound waves to detect and locate submerged objects or measure the distance to the floor of a body of water. (2) An apparatus, as one in a submarine, using sonar. (3) Echolocation.

sone - A subjective unit of loudness, as perceived by a person with normal hearing, equal to the loudness of a pure tone having a frequency of 1,000 hertz at 40 decibels sound pressure level.

sonofusion - Name given by inventor Dr. Rusi P. Taleyarkhan, Purdue University physicist, for his cold fusion experiments combining bursts of ultrasonic high-frequency sound waves with neutron pulses.

sonorous - (1) Having or producing sound. (2) Having or producing a full, deep, or rich sound.

sound - (1) a. Vibrations transmitted through an elastic material or a solid, liquid, or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human ears. Sound (in air) at a particular point is a rapid variation in the air pressure around a steady-state value (atmospheric pressure) - that is, sound is a disturbance in the surrounding medium. b. Transmitted vibrations of any frequency. c. The sensation stimulated in the ears by such vibrations in the air or other medium. d. Such sensations considered as a group. (2) Auditory material that is recorded, as for a movie. (3). Meaningless noise.

sound absorption - The absorption of sound is the process by which sound energy is diminished when passing through a medium or when striking a surface, i.e., sound is attenuated by absorption.

sound bath - Many definitions but generally a meditative experience resulting from an emersion in sound, either music, chanting, chimes, singing crystal bowls, etc., all said to produce calming effects.

soundfield microphone - A specialized microphone array comprised of four cardiod or supercardiod microphones: three to measure left-right, front-back, up-down sound pressure levels and another that measures overall sound pressure level. This arrangement is known as the A-Format, while another one, the B-format, is created by signal processing. This forms the heart of an Ambisonics and other such systems.

sound intensity - The external measured level of a sound, i.e., the sound pressure level. Note that intensity is an objective measurement; contrast with loudness which is a subjective measurement

sound level meter - Electronic instrument for measuring sound pressure levels.

sound masking - The science of using one type of sound to cover up (mask) other sounds.

sound mirrors - Giant parabolic reflector concrete structures used as an early warning system to detect enemy aircraft approaching Great Britain in the 1920s and 1930s before the advent of radar.

sound morphing Combining two sounds to produce a new sound having characteristics of the two originals.

sound occlusion - The phenomenon resulting from wearing solid earplugs, hearing aids or some personal monitors that makes the wearer's voice sound hollow and boomy to themselves, i.e., a voice-in-a-barrel effect.

sound pressure - The value of the rapid variation in air pressure due to a sound wave, measured in pascals, microbars, or dynes - all used interchangeable, but pascals is now the preferred term. Instantaneous sound pressure is the peak value of the air pressure, often used in noise control measurements. Effective sound pressure is the rms value of the instantaneous sound pressure taken at a point over a period of time.

sound pressure level or SPL - (1) A measure of intensity. The rms sound pressure expressed in dB re 20 microPa (the lowest threshold of hearing for 1 kHz). [As points of reference, 0 dB-SPL equals the threshold of hearing, while 140 dB-SPL equals irreparable hearing damage.]

sound reinforcement - the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience.

Sound Shaper® - Registered trademark (now expired) of ADC (Audio Dynamics Corporation) for their line of equalizers/analyzers that pioneered use of RTAs and equalization for the home and studio environment.

Sousa, John Philip (b. 1854-1932) American bandmaster and composer who wrote comic operas and marches such as Stars and Stripes Forever (1897).

sousaphone - A large brass wind instrument, similar in range to the tuba, having a flaring bell and a shape adapted to being carried in marching bands. [After John Philip Sousa.]

spanning tree protocol - A link management protocol providing path redundancy and preventing network loops by defining a tree to span all switches in a network. It forces redundant data paths into a standby (blocked) state. If a path malfunctions, the topology is reconfigured and the link reestablished by activating the standby path.

SPARS (Society of Professional Audio Recording Services) - Founded in 1979, a professional trade organization that unites the manufacturers of audio recording equipment and providers of services with the users. Their goal is worldwide promotion of communication, education and service among all those who make and use recording equipment.

spatial - Of, relating to, involving, or having the nature of space.

Spatializer - A single-ended spatial enhancement technique developed by Desper Products, Inc., a subsidiary of Spatializer Audio Labs, Inc. Widely licensed in both the consumer audio and multimedia computing markets, the Desper, or Spatializer process is normally used as a postprocessor. The Spatializer technology manipulates the original signal in a way that causes the listener to perceive a stereo image beyond the boundaries of the two loudspeakers. It claims to place sounds in front of the listener in an arc of 180 degrees, with excellent imaging and fidelity.

S/PDIF (Sony/Philips digital interface format, also seen w/o slash as SPDIF) - A consumer version of the AES3 (old AES/EBU) digital audio interconnection standard based on coaxial cable and RCA connectors.

Speakon® - A registered trademark of Neutrik for their original design loudspeaker connector, now considered an industry standard.

spectra - A plural of spectrum. In pro audio use, the distribution of frequency of a sound signal, especially the distribution of sound energy, arranged in order of frequency wavelengths.

spectral band replication - An audio coding technology invented by Coding Technologies.

spectrum analyzer - A type of electronic measurement device used to display the amplitude/frequency components of a continuous signal, as opposed to the amplitude/time domain oscilloscope. The formal IEEE definitions are "(1) An instrument generally used to display the power distribution of an incoming signal as a function of frequency. (2) An instrument that measures the power of a complex signal in many bands. The frequency bands can be either constant absolute bandwidth (e.g., FFT analyzer), or constant percentage bandwidth (e.g., RTA analyzer)."

speech interference level (SIL) - The numerical part of the RC noise rating.

speed of sound - The international standard is 331.45 m/s (1087.42 ft/s) at 0 °C (32 °F) and 0% humidity.

spherical wave - Sound waves that radiate out from a point source into open space are concentric spheres.

SPICE (simulation program with integrated circuit emphasis) - A computer circuit analysis program first developed and written by L. W. Nagel and D. O. Pederson of the EECS (Electrical Engineering and Computer Sciences) Department of UC Berkeley.

spider - The assembly which holds the voice coil of a dynamic loudspeaker centered in the magnetic gap. The spider is a corrugated circular piece of specially treated fabric. The name comes from the early days of loudspeakers when it was made of a plastic material that resembled the legs of a spider.

spike fiddle - A type of string instrument in which the neck passes through the sound chest to protrude as a spike at the lower end; the strings are attached to it. The instrument is known in many parts of the Middle East and Central and South-east Asia.

spintronics - Shorten form for spin-based electronics, it describes technology that makes use of the spin state of electrons.

spiral quad - Same as star-quad. A four-conductor cable exhibiting very low noise and hum pickup (hum reduction can be 30 dB better than standard mic cable). The four conductors are wound together in a spiral, and then opposite conductors are joined together at the connectors forming a two-conductor balanced line (also called double balanced) with superior performance.

SPL (sound pressure level) - A measure of intensity. The rms sound pressure expressed in dB re 20 microPa (the lowest threshold of hearing for 1 kHz).

SPL controller - A dynamic processor that maintains (or "levels") the amount of one audio signal based upon the level of a second audio signal.

splitbox - An audio device used to divide one input signal into two or more outputs.

split cue - Headphone cueing system utilizing a pan control to choose between what is cued and what is playing. In its normal mode the cued program feeds one ear and the master, or program (what is playing) feeds the other ear. This makes beat matching easy and convenient since you listen to both turntables (or CDs, or MP3 files, or any combination) at the same time. Rotating the pan control fully CW, or CCW, puts a monoed signal into one ear with no signal going to the other, and vice-versa. Rotating the pan control to its center position routes equal amounts of cue signal to one ear and program signal to the other ear. Pioneered in 1986 by Rane with the introduction of the MP 24 DJ Mixer.

splitter - (aka splitbox) An audio device used to divide one input signal into two or more outputs.

spooler - Comes from the acronym SPOOL derived from simultaneous peripheral operation on-line (also sequential peripheral operations on-line). A program or piece of hardware that controls a buffer of data going to some output device, including a printer or a screen. Spooling temporarily stores programs or program outputs on magnetic tape, RAM or disks for output or processing.

spurious signals - "Any signal(s) in the output of an audio device that are not: the stimulus or program material, harmonic distortion, intermodulation distortion, crosstalk, hum or broadband noise."

SQ - Columbia's (CBS - now Sony Music) name for their quadraphonic sound system using a proprietary matrixing algorithm for encoding four-channel sound down to two-channels. Compare with QS.

SQL (structured query language) - A program used to request information from databases.

SQNR (signal to quantization noise ratio - A measure of the quality of the quantization, or digital conversion of an analog signal. Defined as normalized signal power divided by normalized quantization noise power. The SQNR in dB is approximately equal to 6 times the number of bits of the ADC, for example, the maximum SQNR for 16 bits is approximately 96 dB.

square wave - A periodic waveform characterized by a 50% duty cycle and a Fourier series consisting of odd-ordered, equal phase, sinusoidal harmonic components of its fundamental frequency with amplitudes (coefficients multiplying the magnitude of the fundamental sine wave) equal to 1/n, where n equals the harmonic number. Therefore the first few harmonic amplitudes are 1/3, 1/5, 1/7, 1/9, etc.

SRS (Sound Retrieval System) - A stereo image enhancement scheme invented by Arnold Klayman in the early '80s while working for Hughes Aircraft, and since 1993, marketed by SRS Labs, Inc. A standalone spatial enhancement scheme, SRS benefits from not requiring encoding of the signal, but thus prevents the audio producer from determining the location of individual sound effects. The results vary, being heavily dependent upon the original stereo mix. The goal is to extend the sound field well beyond the limitations of the loudspeakers, and make the overall sound seem more expansive. The elimination of the sweet spot is claimed.

SSID (Service Set Identifier) - A sequence of letters or numbers that is the name of a WLAN (wireless local area network).

standard component values - Standard IEC values for resistors and capacitors per IEC 60063.

standing wave - acoustic resonances 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.

Stanley III, Augustus Owsley - (b. 1935-2011) A '60s icon known as "Bear," he was instrumental in helping create the famous "Wall of Sound" for the Grateful Dead while he was their live sound engineer.

star quad mic cable or quad mic cable - [a term coined by Canare for the first quad mic cable, but was not trademarked and is now a generic term]. A four-conductor cable exhibiting very low noise and hum pickup (hum reduction can be 30 dB better than standard mic cable). The four conductors are wound together in a spiral, and then opposite conductors are joined together at the connectors forming a two-conductor balanced line (also called double balanced) with superior performance.

star topology - (1) A set of three or more branches with one terminal of each connected at a common node. (2) A communications network based on a star pattern where all equipment is connected to a central location with a single path.

state-variable filter - The concept of state-variable is one where a single variable defines one of the characteristics (or states) of a filter (e.g., the gain, or the center/corner frequency, or the Q). The state-variable approach yields independent adjustment of the transfer function pole and zero locations.

St. Croix, Stephen Curtis - (b. 1948-2006) American inventor, musician, engineer and producer who founded Marshall Electronic and changed his last name from Marshall to St. Croix because he loved the islands. Along with John Ariosa he developed the Marshall Time Modulator in 1976, one of the earliest audio delay units. He wrote The Fast Lane column, for Mix magazine for 20 years, now available in book form from MIX as Life in the Fast Lane.

steganography - The science of communicating in a way that hides the existence of the actual communication. The practice of hiding information in a wider bandwidth carrier. This field covers the techniques used in digital watermarking schemes.

Steinberg, John C. - (b. 1895-1988) American engineer who worked with Snow and in 1936 co-patented an improved three channel stereophonic system as U.S. Patent #2,126,929.

Steinmetz, Charles Proteus - (b. 1865-1923) A German-American mathematician and engineer who first developed the mathematics (based on complex numbers) describing alternating current.

Steinweiss, Alex - (b.1916- ) The father of the album cover, he designed the first album cover in 1939 for Columbia Records where he worked as their first art director.

stems - (1) Nickname for the individual tracks used to create the final mix and saved for remixing purposes. Origin is from movie soundtracks where there are three main stems: dialog, music and effects. (2) The vertical line extending from the head of a note found in music notation.

stereo or stereophonic sound - (1) "The word stereophonics was derived by combining two Greek words: stereo, which means solid and implicates the three spatial dimensions (depth, breadth, and height), and phonics, which means the science of sound. Thus, stereophonics denotes the science of 3-dimensional sound" [Streicher & Everest]. (2). Term applied to any system of recording (or transmission) using multiple microphones for capturing and multiple loudspeakers for reproduction the sound. Stereo as the term has become popularly used restricts the number of playback loudspeakers to two, but strictly speaking the term can apply to any number of loudspeakers. Although stereo was first demonstrated at the Paris Opera in 1881 using carbon microphones and earphones, it would not become widespread until the work of Blumlein in the 1930s.

Stereobelt - The first portable stereo cassette player, developed by Andreas Pavel in 1972.

stereo disc lathe - Invented by Neumann in 1956, the invention that opened the door to the modern stereo LP record.

stereo imaging - Usually refers to the localization of sounds in a two-channel (normally) stereo sound system, i.e., left-to-right (or vice versa) apparent performer positions.

STI (speech transmission index) - An objective measure to predict the intelligibility of speech transmitted from talker to listener by a transmission channel.

STIpa (speech transmission index for public address systems) - A speech intelligibility measurement described by developers H. Steeneken, J. Verhave, S. McManus and K. Jacob in their paper "Development of an Accurate, Handheld Simple-to-Use, Meter for the Prediction of Speech Intelligibility," Proc. IOA, Vol. 23, Pt. 8, 2001.

stiction - In positioning, the friction that prevents immediate motion when force is first applied to a body or surface at rest.

stochastic resonance - The science behind dither. A phenomenon of nonlinear systems where low-level input signals are amplified and optimized by adding noise, i.e., an increase in the input noise produces an improvement in the output signal-to-noise ratio "The effect requires three basic ingredients: (i) an energetic activation barrier or, more generally, a form of threshold; (ii) a weak coherent input (such as a periodic signal); (iii) a source of noise that is inherent in the system, or that adds to the coherent input. Given these features, the response of the system undergoes resonance-like behavior as a function of the noise level; hence the name stochastic resonance." [From Stochastic Resonance by L Gammaitoni, P Haenggi, P Jung, and F Marchesoni.]

Stockham, Jr., Thomas G. - (b. 1934-2004) American electrical engineer best known for his pioneering work in digital audio recording and editing. Known as the father of digital magnetic sound recording, Dr. Stockham earned Grammy, Emmy and Academy awards for his work and was the founder of Soundstream, Inc.

Stockhausen, Karlheinz - (b. 1928-2007) German composer renowned for his pioneering work in electronic music.

stopband - The range of frequencies substantially attenuated by a filter as opposed to the range of frequencies unaffected by the filter. The opposite of passband.

STP (shielded twisted-pair) - Standard two-conductor copper cable, with insulation extruded over each conductor and twisted together. Usually operated as a balanced line connection and shielded.

STP (spanning tree protocol) - A link management protocol providing path redundancy and preventing network loops by defining a tree to span all switches in a network. It forces redundant data paths into a standby (blocked) state. If a path malfunctions, the topology is reconfigured and the link reestablished by activating the standby path.

strad - Affectionate nickname for instruments made by Stradivari, Antonio (b. 1644-1737) Italian violinmaker who developed the proportions of the modern violin and created instruments of unsurpassed beauty and tone. His sons Francesco (1671-1743) and Omobono (1679-1742) carried on the family tradition of fine artistry.

streaming media - A process in which audio, video, and other multimedia is delivered "just in time" over the Internet or company intranet.

stripline - A flat transmission line surrounded by a dielectric between a pair of ground planes. Contrast with microstrip.

stutter edit - A popular DJ remixing effect.

subcardioid microphone - A cardioid-shaped response that does not tuck-in or null at the rear, instead has a smooth flat response to the rear.

subcode - Non-audio digital data encoded on a CD that contains definable information such as track number, times, copy inhibit, copyright, etc.

subgroups - A combination of two or more signal channels gathered together and treated as a set that can be varied in overall level from a single control or set of controls. Mixing consoles often provide a group function mode, where the level of any group of incoming singles may be adjusted by a single slide fader, which is designated as the group fader.

subharmonic - Frequencies that are fractions of the fundamental, i.e., multiples of 1/2, 1/3, 1/4 etc.

submix - A combination of two or more signal channels gathered together and treated as a set that can be varied in overall level from a single control or set of controls. Mixing consoles often provide a group function mode, where the level of any group of incoming singles may be adjusted by a single slide fader, which is designated as the group fader.

subsonic - Having a speed less than that of sound in a designated medium.

subwoofer - A large woofer loudspeaker designed to reproduce audio's very bottom-end, i.e., approximately the last one or two octaves, from 20 Hz to 80-100 Hz.

successive approximation - Early method of A/D conversion.

supra-aural - Literally "on the ear," thus headphones with earpieces resting on the ear.

supercardioid microphone - cardioid-shaped response that includes small pickup directly to the rear.

supersonic - Having, caused by, or relating to a speed greater than the speed of sound in a given medium, especially air.

suppression also gain suppression - In teleconferencing the term used to describe the technique of instantaneous reduction of a sound system's overall gain to control acoustic feedback and thus reduce echoes.

surface transfer impedance - the standard measurement used for quality rating of the RF shielding performance of cables, connectors and shield terminations. It measures how much voltage appears on the inner wires when the shield is driven by a strong RF signal and defines ZT as the induced voltage divided by the shield test current.

surround - The circular ring mechanism that attaches the cone to the frame ("surrounding" the cone), usually rolled (allows greater throw) and made from foam or rubber material.

surround sound - Generic term for sound systems using more than mono (one front channel), or stereo (two left-right channels) loudspeakers to create a two- or three-dimensional experience.

susceptance - The reciprocal of reactance, i.e., the imaginary part of the admittance . It is measured in siemens. Its mathematical symbol is “B”

sustain - A prolonged note, especially the ability to maintain a note beyond its natural decay.

S-video (also called Y/C video) -, a two-channel video channel that transmits black and white, or luminance (Y), and color portions, or chrominance (C), separately using multiple wires. This avoids composite video encoding, such as NTSC, thus providing better picture quality.

Swanson Sound Service - Founded in 1926, in Oakland, California by Art Swanson, the Swanson Sound Service company, along with R.G. Jones (near London) are considered the first sound companies, and both are still going strong.

Sweet Sixteen - Nickname for a briefly popular loudspeaker design in the early '60s using sixteen 5-inch speakers per channel arranged in a 4 x 4 array on a flat baffle.

SWG (standard wire gauge) - British or Imperial standard wire gauge standard.

switch-mode power supply - An electronic power supply characterized by switching a power transistor on and off with a variable duty cycle whose average is the desired output voltage.

SWR - the ratio of the magnitude of the transverse electric field in a plane of maximum strength to the magnitude at the equivalent point in an adjacent plane of minimum filed strength.

symmetrical (reciprocal) response - Term used to describe the comparative shapes of the boost/cut curves for variable equalizers. The cut curve exactly mirrors the boost curve.

Syn-Aud-Con (Synergetic Audio Concepts) - A private organization conducting audio seminars and workshops, sponsored by several pro audio companies.

synesthesia also synaesthesia - (1) A condition in which one type of stimulation evokes the sensation of another, as when the hearing of a sound produces the visualization of a color. (2) A sensation felt in one part of the body as a result of stimulus applied to another, as in referred pain. (3) The description of one kind of sense impression by using words that normally describe another.

synchronous - A transmission process where the bit rate of the signal is fixed and synchronized to a master clock.

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