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:
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
(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
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
TDIF (Teac digital interface format) Tascam's (Teac)
8-channel digital audio interface to their
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
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
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
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:
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
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
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:
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.
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
not generally thought of as transducers, photocells, LEDs
(light-emitting diodes), and even common light bulbs are
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.