Term	Definition	Demo
Tangential Modes	See Room Resonances.
TDS	See: Time Delay Spectrometry.
Television Systems	Three incompatible systems exist in the world. NTSC has 525 lines, presented at 60 fields/second (about 480 picture lines), while both PAL and SECAM have 625 lines presented at 50 fields/second (about 576 picture lines). All of these are used for broadcast, cable and satellite transmission, as well as for DVD-video. See: NTSC, PAL, SECAM, Field, Raster, Scan Lines.
Temporal Masking	Masking that occurs when a loud transient sound prevents us from hearing sounds that occur just earlier (backward masking) and just later (forward masking) in time. See Masking, Threshold Shift.
Terrestrial	Jargon for radio and television signals that propagate normally from a transmitter on the ground (terrestrial) to a conventional antenna. Also called over the air (OTA).
Three-Way Loudspeaker	See: Loudspeaker System.
Threshold of Pain	When sound levels are sufficiently high as to cause discomfort, or pain, in the ears of listeners. Very approximately, 110+ dB, as it varies with individual listeners and with the kind of sound.
Threshold Shift	A change, normally an elevation, in the hearing threshold. It can be permanent, as in hearing loss, or temporary, as occurs when the audibility of some sounds is reduced by the presence of others, in masking. See Masking, Hearing Loss.
Throat	In a horn loudspeaker, this is the smallest part, where the sound leaves the driver begins its travel down the expanding flare of the horn itself. See: Horn, Compression Driver, Phase Plug.
THX	THX was created by George Lucas to apply performance standards to cinema sound systems ensuring the playback quality of film sound tracks. Named after his first feature film, THX 1138. Expanded into home audio, and other areas. THX is now a private licensing company issuing certifications, paid for by manufacturers, that products meet certain performance standards, and incorporate certain functions, some of which are proprietary. There are levels of certification, from very basic to high. It is a reassurance to customers, but it needs to be noted that non-THX-certified products can also offer performance that is as good or better.
Timbre	The essential distinctive perceived quality of a sound, separate from loudness and pitch. That which allows us to recognize whether the same note has been played by a piano or a guitar, a clarinet or a trumpet, or sung by Pavarotti or Sinatra.
Time-Delay Spectrometry	A measurement system that allows one to examine events in time as well as frequency, and to isolate a direct sound from later reflected sounds in a normal room, thus approximating anechoic measurements. There are trade-off's though. As the measurement time window is shortened, e.g. to eliminate later reflections, the frequency resolution of the measurement is reduced. An anechoic measurement space is still desirable. See: Anechoic, Direct Sound.
Tinnitus	A ringing in the ears that accompanies temporary hearing loss after exposure to loud sounds, or that becomes permanent for some individuals unfortunate enough to incur permanent hearing loss.
Tone Burst	A time sample of a single frequency (pure tone) which contains some number of complete cycles. The burst may be turned on gradually or abruptly, all of which affects the spectrum of the signal and how it sounds. Once a pure tone is interrupted, it no longer has a single frequency spectrum.
Tone Control	A simple filter that can boost or cut portions of the audio frequency range, used to change the tonal balance of reproduced sound. See Bass Control, Treble Control, Equalizer.
Transducer	A device that converts energy from one form to another. For example, a microphone converts acoustical energy into electrical energy, while a loudspeaker does the reverse.
Transfer Function	An input-to-output measurement of performance that includes both amplitude and phase as functions of frequency. The Fourier transform of the transfer function is the impulse (time) response of the system. See: Frequency Response, Phase Response, Fourier Transform, FFT.
Transform	A computational procedure or set of rules by which a signal can be converted from one form into another. See Fourier Transform.
Transformer	An electronic component consisting of two or more coils of wire in close proximity, allowing the transfer of energy from one to the other by means of inductive coupling. Many applications, including electrical isolation, voltage transformation, impedance matching, etc.
Transient Response	A measure of the time domain response of a system, input-to-output, to a very brief transient signal at its input. It is widely believed that the time-domain behavior of a device is independent of the frequency response. However, the Fourier transform of this time-domain waveform is the frequency-domain transfer function. See: Impulse Response, Transfer Function, Fourier Transform, FFT.
Transparency	The objective of every maker of windows, and conscientious loudspeaker manufacturers, who attempt to provide a transparent - i.e. unmodified - rendering of an audio work of art.
Treble	High-frequency audio signals
Treble Control	A tone control allowing the user to boost or cut the high frequency portion of the audio signal.
Tuned Port Bass Enclosure	See Bass Reflex
Tuner	A device that tunes, or selects, radio or television stations from broadcast signals received on a terrestrial antenna, by cable or satellite.
Tweeter	A loudspeaker driver optimized to reproduce high frequencies, typically above about 2kHz to 4kHz.
Two-Way Loudspeaker	See: Loudspeaker System.