Glossary of Audio Terminology

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Index | References



70 volt line See: constant-voltage

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 which captures and holds an analog signal for a finite period of time. 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 32kHz, 48kHz, and 50kHz. [Historical note re 44.1kHz vs. 44.056kHz: Since the first commercial digital audio recorders used a standard helical scan video recorder for storage, there had to be a fixed relationship between sampling frequency and horizontal video frequency, so these frequencies could be derived from the same master clock by frequency division. For the NTSC 525-line TV system, a sampling frequency of 44,055.94 Hz was selected, whereas for the PAL 625-line system, a frequency of 44,100 Hz was chosen. The 0.1% difference shows up as an imperceptible pitch shift.]

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

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.

SCMS (pronounced "scums") (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.

SCSI port (pronounced "scuzzy") (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) See: DVD

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. Sony recently developed a single camera system that records all three digital formats (Dolby Digital, DTS & SDDS) on a single inventory print, thus setting the stage for long term coexistence of all formats.

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.

SECAM (Sestem En Couleur Avec Memoire - "Sequential Color with Memory") The analog video standard used for television broadcast and composite video connections in France, former French colonies in the Middle East an Africa, and in former communist countries throughout  most of Eastern Europe. SECAM was introduced in the early 1960's an first adopted in 1967 in France.  SECAM signals encode the video as 625 horizontal lines of pixels scanned in odd and even sets at 1 Field (1/2 frame) every 50th of a second (to work with the European  power standard of 50cps), resulting in am effective video frame rate of 25fps. Because of its similarity with PAL (same resolution, same frame rate and same bandwidth), all of the modern video systems, such as DVD, VCD and SuperVHS use PAL internally (for storing the data in the storage media, etc) and just change the color encoding to SECAM when set to output the signal back to a SECAM TV or monitor. SECAM is one of three main television standards throughout the world. See PAL and NTSC

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

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.

servo-loop; -locked loop; -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 which 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. See: servo-loop

Shannon, Claude E. (1916- ) American mathematician and physicist who is credited as the father of information theory. In his master's thesis Shannon showed how an algebra invented by the British mathematician George Boole in the mid-1800s could represent the workings of switches and relays in electronic circuits. His paper has been called "possibly the most important master's thesis in the century."

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.

sibilant Linguistics. adj. 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) See: DIM/TIM

sigma-delta See: delta-sigma modulation

signal-to-noise ratio See: S/N

sine Abbr. sin Mathematics. 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 Mathematics. The graph of the equation y = sin x. Also called sinusoid.

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

sinusoid Mathematics. See: sine curve

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. Mathematics. 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).

smoke From the phlogiston theory of electronics, it is smoke that makes ICs and transistors work. The proof of this is self-evident because everytime 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. (Incidently wires carry smoke from one device to another.) [Origin unknown but classic.]

smoothing filter See: anti-imaging filter

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

SNMP (Simple Network Management Protocol) The most common method by which network management applications can query a management agent using a supoported 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.

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.

Software Any program or routine ( such as an application, system file or device driver) that furnishes instructions or data to the computer for processing.  These are the components of a computer system that are logical, not physical (hardware).  Software is also sometimes misused to refer to video, photos, audio and any other type of data that can be handled by the computer.

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).

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.

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. 4. Music. A distinctive style, as of an orchestra or a singer.

sound off To express one's views vigorously: He was always sounding off about his boss.

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 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.] See: inverse square law

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. Often confused with NARAS.

Spatializer A single-ended spatial enhancement technique developed by Desper Products, Inc., a subsiderary 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 which 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 AES/EBU digital audio interconnection standard based on coaxial cable and RCA connectors.

SPL controller See: leveler

SPL See: sound pressure level

splitter An audio device used to divide one input signal into two or more outputs. Typically this type of unit has one input with 6-16 (or more) outputs, each with a level control and often is unbalanced. See: distribution amplifier

spooler Comes from the acronym SPOOL derived from Simultaneous Peripheral Operation 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 temporaily stores programs or program outputs on magnetic tape, RAM or disks for output or processing. And you thought you were done learning for the day -- HA!

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.

Standards  Uniform specifications to permit interoperability between devices from different manufactures or countries.  Standards consist of guideline documentation that reflects agreements on products, practices, or operations by nationally or internationally recognized industrial, professional, trade associations or governmental bodies. Note:  This concept applies to formal, approved standards, as contrasted to de facto standards and proprietary standards, which are exceptions to the rule.( i.e. anything Microsoft )

stereo 3-way, etc. See: active crossover

Streaming  Technology that is capable of playing audio and/or video before the complete data file has had time to download.

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

subgroups See: groups

submix See: groups

subsonic Having a speed less than that of sound in a designated medium. [Use infrasonic if referring to frequencies below human hearing range.]

subtend 1. Mathematics. To be opposite to and delimit: The side of a triangle subtends the opposite angle. 2. To underlie so as to enclose or surround: flowers subtended by leafy bracts.

Super Audio CD See: DSD

supersonic Having, caused by, or relating to a speed greater than the speed of sound in a given medium, especially air. [Use ultrasonic if referring to frequencies above human hearing range.]

SVGA (Super Video Green ArraySuper Video Graphics Array) A video graphics ddisplay mode standard.  referring to a video adapter capable of a resolution of up to 800 by 600 pixels.

sweet spot Any location in a two loudspeaker stereo playback system where the listerner is positioned equidistant from each loudspeaker. The apex of all possible isosceles (two equal sides) triangles formed by the loudspeakers and the listener. In this sense, the sweet spot lies anywhere on the sweet plane extending forward from the midpoint between the speakers.

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.

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

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



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