3-dB down point See: passband

3D sound A term used to describe a three-dimensional sound field. A true 3D sound field positions sound anywhere in a semi-spherical shell surrounding the listener. Sound must come from anywhere directly behind to directly overhead to directly in front of the listerner and all points left and right. It if does not, it is not 3D sound. The term is popularly misused by multimedia companies to describe systems, effects and techniques purported to create 3D sound from two sources and designed for two loudspeaker playback; however, the result is not 3D sound. It is enhanced two-dimensional sound. Strictly speaking a broadening, widening, enhancing, or spreading of the left/right sound stage is not 3D. No two loudspeaker system is capable of locating sounds directly to the rear of the listener; nevertheless, some of these systems truly impress. The best enhancement schemes come very close to recreating a quarter-spherical sound shell, extending to nearly 180 degrees left-to-right, approaching 90 degrees overhead, with greatly improved depth of field.

10Base-T, 100Base-T, 1000Base-F See: Ethernet

T Carrier System  The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission.  T Carrier systems use pulse code modulation and time-division multiplexing. The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time)

T-1 A digital transmission protocol  utilizing two twisted-pairs with a maxim capacity of 1,544Kbps.  Usually provisioned by a local of long distance telephone carrier as a leased line.  Commonly used for connecting networks across remote distances.  May also be used in telephony systems to provide enough bandwidth to handling up to 24 simultaneous digital voice channels.

T-3 A digital transmission protocol  utilizing two twisted-pairs with a maxim capacity of 45Mbps.  Usually provisioned by a local of long distance telephone carrier as a leased line.  Commonly used for backbone connections for corporate and ISP networks across remote distances.

T-Coil ( Telephone Coil )  A device, usually found in hearing aids that is used to pick up a audio signal from a local electromagnet field.  T-coils were originally designed to work with telephone receivers.  They may also be used with other devices designed to aid the hearing impaired including neck loops, induction pads and room induction loop systems.

talkback 1. A recording console feature where a microphone mounted on the console allows the engineer to speak with the musicians during sessions -- a very useful feature when the console is located in a soundproof control room, or out in the audience for sound reinforcement systems.

TCP/IP (transmission control protocol/internet protocol) A set of protocols developed by the Department of Defense in the '70s to link dissimilar computers across many kinds of networks and LANs. Popular with Ethernet users.

TDIF (Teac digital interface format) Tascam's (Teac) 8-channel digital audio interface to their DA-88 digital multitrack recorder, using unbalanced signal transmission and a DB-25 type connector.

TDM (time division multiplexing)

TDS (time-delay spectrometry) A sound measurement theory and technique developed in 1967 by Richard C. Heyser at the Jet Propulsion Laboratories of the California Institute of Technology.

TEF (time-energy-frequency) The term adopted to describe the entire spectrum of TDS measurements, including energy-time curves. Popularized by Richard Heyser through his participation in Synergetic Audio Concepts seminars. Made practical in 1979 by the Techron division of Crown International - Cal Tech's first TDS licensee, and introduced as the TEF System 10.

telecommunication Communicating over a distance by wire, fiber or wireless means.

teleconferencing A conference held by three or more persons over a distance. Normal useage refers to voice conferencing, also termed audioconferencing which includes all forms of audio. The term is sometimes extended to include video and document, or data, conferencing. Note that the term does not mean telephone conferencing, but rather distance conferencing, although telephone lines are often used.

THD (total harmonic distortion) A measurement technique rarely used, but often confused with the THD+N technique described below. Many people mistakenly refer to a "THD" measurement when they really mean the "THD+N" technique. [A true THD measurement consists of a computation from a series of individual harmonic amplitude measurements, rather than a single measurement. "THD" is the square root of the sum of the squares of the individual harmonic amplitudes. And the answer must specify the highest order harmonic included in the computations; for example, "THD through 8th harmonic."

THD+N (total harmonic distortion plus noise) The most common audio measurement. A single sine wave frequency of know harmonic purity is passed through the unit under test, and then patched back into the distortion measuring instrument. A measurement level is set; the instrument notches out the frequency used for the test, and passes the result through a set of band-limiting filters, adjusted for the bandwidth of interest (usually 20-20kHz). What remains is noise (including any AC line [mains] hum or interference buzzes, etc.) and all harmonics generated by the unit. This composite signal is measured using a true RMS detector voltmeter, and the results displayed. Often a resultant curve is created by stepping through each frequency from 20 Hz to 20kHz, at some specified level (often +4 dBu), and bandwidth (usually 20 kHz; sometimes 80 kHz, which allows measurement of any 20 kHz early harmonics). [Note that the often-seen statement that "THD+N is x%," is meaningless. For a THD+N spec to be complete, it must state the frequency, level, and measurement bandwidth.] While THD+N is the most common audio test measurement, it is not the most useful indicator of a unit's performance. What it tells the user about hum, noise and interference is useful; however that information is better conveyed by the signal-to-noise (S/N) ratio specification. What it tells the user about harmonic distortion is not terribly relevant simply because it is harmonically related to the fundamental, thus the distortion products tend to get masked by the complex audio material! The various intermodulation (IM) distortion tests are better indicators of sonic purity.

third-octave Term referring to frequencies spaced one third of an octave apart.  More appropriate an far less misleading term is  one-third octave. While it can be argued that "third" can also mean one of three equal parts, and as such might be used to correctly describe one part of an octave spit into three equal parts, it is potentially too confusing. The preferred term is one-third octave.

Thompson filters See: Bessel crossover

THX® Lucasfilm, Ltd. term meaning several things: 1) Their audio playback design and certification program for commercial cinema theaters; 2) Their audio playback specification for home cinema systems; 3) Approved audio/video playback equipment meeting their standards of quality and performance; and 4) Laserdiscs and VHS tapes mastered by them to meet their quality and performance standards. The term comes from two sources: George Lucas's first film THX-1138, and a somewhat tongue-in-cheek reference to Tomlinson Holman's eXperiment, after their original technical director, patentee and creative force behind all the above, now runs TMH Corporation.

TIA (Telecommunications Industry Association) Created in 1988 by a merger of the US Telecommunications Suppliers Association (USTSA) and the EIA's Information and Telecommunications Technologies Group (EIA/ITG). This organization works with the EIA in developing technical standards and collecting market data for the telecommunication industry.

TIM (transient intermodulation distortion) See: IM

timbre (pronounced "tambur") 1. The quality of a sound that distinguishes it from other sounds of the same pitch and volume. 2. Music. The distinctive tone of an instrument or a singing voice.

time 1.a. A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future. b. An interval separating two points on this continuum. c. A number, as of years, days, or minutes, representing such an interval. d. A similar number representing a specific point on this continuum, reckoned in hours and minutes. 2. Music. a. The characteristic beat of musical rhythm: three-quarter time. b. The rate of speed at which a piece of music is played; the tempo.

time delay Used to describe the time passed during processing of a digital signal.  Can be confusing, better terms are signal delay or just delay.

tone 1. Music. a. A sound of distinct pitch, quality, and duration; a note. b. The interval of a major second in the diatonic scale; a whole step.  2.a. The quality or character of sound. b. The characteristic quality or timbre of a particular instrument or voice.

tone controls The term most often referring to a two-band shelving equalizer offering amplitude control only over the highest (treble, from music, meaning the highest part, voice, instrument, or range) frequencies, and the lowest (bass, from music, meaning the lowest musical part) frequencies. Sometimes a third band is provided for boost/cut control of the midband frequencies. See also: Baxandall tone controls

toroid The name for any doughnut-shaped body. [Mathematics: a surface generated by a closed curve rotating about, but not intersecting or containing, an axis in its own plane.] The shortened popular name for the doughnut-shaped (toroidal) transformers common to audio equipment; favored for their low hum fields.

TOSLINK(Toshiba link) A popular consumer equipment fiber optic interface based upon the S/PDIF protocol, using an implementation first developed by Toshiba.

transducer  A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antenna. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.

transversal equalizer A multi-band variable equalizer using a tapped audio delay line as the frequency selective element, as opposed to bandpass filters built from inductors (real or synthetic) and capacitors. The term "transversal filter" does not mean "digital filter." It is the entire family of filter functions done by means of a tapped delay line. There exists a class of digital filters realized as transversal filters, using a shift register rather than an analog delay line, with the inputs being numbers rather than analog functions.

truncate To eliminate without round-off some low-order bits, often after performing an arithmetic computation.

TTL (transistor transistor logic) The workhorse digital logic integrated circuit family introduced as a standard product line in 1964.

twisted-pair Standard two conductor copper cable, with insulation extruded over each conductor and twisted together. Usually operated as a balanced line connection. May be shielded or not.