Direct Drive Image Light
Amplifier. This Hughes/JVC technology uses a reflective LCD to create
an image. A light source is then reflected off the reflective LCD and
is directed through a lens to a screen.
A Digital to Audio Converter. Converts a digital bitstream to an analog
signal. Can be a separate unit or an internal chip set.
Direct Current. Current that moves in only one direction.
An acronym found on CD cases to indicate that the music was recorded
(D) and mastered (D) and stored (D) digitally. (See also ADD
) (See also AAD
In a loud speaker - the separating of each drive unit from its
enclosure, and also each enclosure from the others, such that no
vibration is transmitted from one to another.
Named after Alexander Graham Bell. A logarithmic measurement unit that
describes a sound's relative loudness, though it can also be used to
describe the relative difference between two power levels. A decibel is
one tenth of a Bel. In sound, decibels generally measure a scale from 0
(the threshold of hearing) to 120-140 dB (the threshold of pain). A 3dB
difference equates to a doubling of power. A 10dB difference is
required to double the subjective volume. A 1dB difference over a broad
frequency range is noticeable to most people, while a 0.2dB difference
can affect the subjective impression of a sound.
- 0 dB is the threshold of hearing
- 130 dB is the threshold of pain.
- Whisper: 15-25 dB
- Quiet background: about 35 dB
- Normal home or office background: 40-60 dB
- Normal speaking voice: 65-70 dB
- Orchestral climax: 105 dB
- Live Rock music: 120 dB+
- Jet aircraft: 140-180 dB
difference between a sonic event and its perception at the listening
position (sound traveling through space is delayed according to the
distance it travels). People perceive spaciousness by the delay between
the arrival of direct and reflected sound (larger spaces cause longer
The part of a dynamic loudspeaker attached to the voice coil that moves
and produces the sound. It usually has the shape of a cone or dome.
Insulating materials exposed to electric fields are called dielectrics.
Dielectrics are necessary parts in the construction of any cable
because they prevent oxidation and keep the conductors from touching
one another. In audio cables, relatively low voltage and current levels
mean that dielectric strength is not the most important factor. Far
more significant in its effect on the sound is a material's dielectric
absorption. This characteristic describes the way a dielectric may
discharge a secondary signal into the conductor out of phase with the
As a current is passed through a conductor, an
electromagnetic field is created which interacts with the dielectric
material and temporarily displaces the molecular structure. If the
dielectric material has good elasticity and can return quickly to its
normal state, then the material is said to have low dielectric
hysteresis or loss and will have little audible effect on the signal.
The re-radiation of sound waves at discontinuities such as cabinet
edges. The time-delayed wave interferes with the original sound output,
causing peaks and dips in the frequency response and smearing the
In audio, the scattering of sound waves, reducing the sense of
localization. In video, the scattering of light waves, reducing hot
spotting, as in a diffusion screen.
Acoustical treatment device that preserves sound energy by reflecting
it evenly in multiple directions, as opposed to a flat surface, which
reflects a majority of the sound energy in one direction.
Represented by a numerical code. For sound, the conversion of an
analogue waveform to a series of numbers representing the instantaneous
amplitude for each sample taken, the storage of those numbers, and the
eventual conversion back to analog format for replay.
An encoding system that digitally compresses up to 5.1 discrete
channels of audio (left front, center, right front, left surround,
right surround, and LFE) into a single bitstream, which can be recorded
onto a DVD, HDTV broadcast, or other form of digital media. When
RF-modulated, it was included on some laser discs, which requires an
RF-demodulator before the signal can be decoded. Five channels are
full-range; the .1 channel is a band-limited LFE track. A Dolby Digital
processor (found in most new receivers, preamps, and some DVD players)
can decode this signal back into the 5.1 separate channels. Most films
since 1992's Batman Returns have been recorded in a 5.1 digital format,
though a number of films before that had 6-channel analog tracks that
have been remastered into 5.1.
(Dolby Digital and Pro-Logic are registered trademarks of Dolby Laboratories Inc.) (See also AC3)
Speakers with drivers on opposite faces that are wired electrically out
of phase, creating an area of cancellation to the sides. Recommended by
THX for use as surround speakers, with null directed at the listener to
create a more ambient and non-localizable effect.
Direct View Television
Display whose image is created on the surface from which it is viewed.
The spreading of sound waves as they leave a source. The spreading of sound waves as they leave a source.
in a midrange driver in place of a conventional dust cap. It improves
dispersion in the mid-frequencies, and helps to maintain the high
frequency response of midrange units.
The method used in digital systems to smooth out the transitions from
one bit to another at low levels. Dither makes a digital recording
sound and behave more like analog. The better a recording is dithered,
the higher its apparent resolution.
Digital Light Processing. A Texas Instruments process of projecting
video images using a light source reflecting off of an array of tens of
thousands of microscopic mirrors. Each mirror represents a pixel and
reflects light toward the lens for white and away from it for black,
modulating in between for various shades of gray. Three-chip versions
use separate arrays for the red, green, and blue colors. Single-chip
arrays use a color-filter wheel that alternates each filter color in
front of the mirror array at appropriate intervals. (See also DMD)
Digital Micromirror Device. Texas Instruments engine that powers DLP
projectors. Uses an array with tens of thousands of microscopic mirrors
that reflect a light source toward or away from the lens, creating an
image. Each mirror represents a pixel. (See also DLP)
Dynamic Noise Reduction. A signal-processing circuit that attempts to
reduce the level of high-frequency noise. Unlike Dolby NR, DNR doesn't
require preprocessing during recording.
Dolby Digital EX Surround
An enhancement to the Dolby Digital 5.1 where a rear center channel has
been added creating a 6.1 format. The Dolby Digital Surround EX format
does not add an additional discreet recorded channel. The new rear
center channel is matrix-encoded in the Dolby Digital left and right
surround signals. The recorded Dolby Digital audio consists of five
discrete main channels and a sixth, low-frequency-effects (LFE)
channel. The two rear surround channels carry the signal for the rear
center channel. The Dolby Digital Surround EX format made is debut in
the 1999 movie Star Wars Episode I - The Phantom Menace.
Dolby Pro Logic
An earlier form of surround sound. Four separate signals are encoded in
a 2-channel recording and re-separated by the processor into left,
centre, right and surround channels. The surround channel is usually
fed to 2 speakers at the rear. (Dolby and Pro-Logic are registered
trademarks of Dolby Laboratories Inc.) (See also Dolby Surround)
Developed by Dolby in the early 70s, Dolby Stereo produces 4 channel
sound with three channels of sound in the front (left and right for
music and effects and centre for dialogue) and a surround channel for
effects and atmospheres.
Encodes sound for rear effects channels into the stereo tracks. Needs
to be replayed through a decoder to produce surround. (Dolby is a
registered trademark of Dolby Laboratories Inc.) (See also Dolby Stereo)
A high frequency speaker with a dome-shaped diaphragm.A high frequency speaker with a dome-shaped diaphragm.
speaker without an enclosure; also refers to the active element of a
speaker system that creates compressions and rarefactions in the air.
Direct Stream Digital. A digital encoding format proposed by Sony and
Philips used to record SACD albums. DSD samples an audio signal at a
fixed rate (frequency) just as in the PCM method. However, instead of
recording the volume or amplitude as an absolute number, as in PCM, the
DSD method measures and records how much the volume has changed since
the last measurement. If the signal is sampled fast enough, the amount
of change since the previous sample would be very small. The proposal
for DSD is for a sampling rate that's over 2 MHz (2 million times per
second). At this high speed the changes in signal strength can be
represented with one bit. DSD also compresses the data resulting in a
2:1 reduction. DSD will be able to provide a frequency response from DC
to 100 kHz with a dynamic range of 120 dB.
Digital Signal Processing. DSP can be used to create equalization, compression, etc. of a digital signal.
Digital Theater Systems. Multi-channel digital surround system that
encodes and decodes audio signals enhancing the fidelity of the signal
to produce high quality sound. It is used in some movie theatres and is
also available in some home theatre digital processors. (See also 5.1 Surround Sound)
An enhanced version of the 5.1 DTS system. Like Dolby's Surround EX, a
sixth channel is added. In some cases (DTS ES Discrete), the sixth
channel is discrete. Software is backwards-compatible with 5.1 systems,
but requires an ES or 6.1 processor to obtain additional benefit. Neo:6
is a subset of DTS ES that creates 6.1 from material with fewer
Television. Umbrella term used for the ATSC system that will eventually
replace our NTSC system in 2006. HDTV is a subset of the DTV system.
While the FCC does not recognize specific scan rates in the adopted DTV
system, typically accepted rates include 480i, 480p, 720p, and 1080i.
Dual / Double Voice Coil (DVC)
A voice coil with two windings, generally used in woofers. Each voice
coil can be connected to a stereo channel, or both voice coils can be
wired in parallel or series to a single channel.
known as the Digital Video Disc, though marketers unofficially refer to
it as the Digital Versatile Disc. DVD uses a 5-inch disc with anywhere
from 4.5 Gb (single layer, single-sided) to 17 Gb storage capacity
(double-layer, double sided). It uses MPEG2 compression to encode
720:480p resolution, full-motion video and Dolby Digital to encode 5.1
channels of discrete audio. The disc can also contain PCM, DTS, and
MPEG audio soundtracks and numerous other features. An audio-only
version, DVD-A uses MLP to encode six channels of 24-bit/96-kHz audio.
DVD Audio (DVD-A)
An audio standard for high quality audio recorded on DVD's that exceed
the capacity and quality of CD's. An DVD-Audio disk is capable of
recording audio with frequencies up to 96Khz (compared to CD's at
20kHz) and with a dynamic range of up to 144dB (compared to CD's 96dB).
DVD-Audio supports multi-channel recordings.
Digital Visual Interface. Connection standard developed by Intel for
connecting computers to digital monitors such as flat panels and DLP
projectors. A consumer electronics version, not necessarily compatible
with the PC version, is used as a connection standard for HDTV tuners
and displays. Transmits an uncompressed digital signal to the display.
The latter version uses HDCP copy protection to prevent unauthorized
copying. (See also HDMI
The ability of an audio device to respond to musical peaks. For
example, an amplifier may only be capable of a sustained 100 watts, but
may be able to achieve peaks of 200 watts for the fraction of a second
required for an intense, quick sound. In this example the dynamic
headroom would equal 3 db.
The range between the loudest and the softest sounds that are in a
piece of music, or that can be reproduced by a piece of audio equipment
without distortion (a ratio expressed in decibels). In speech, the
range rarely exceeds 40 dB; in music, it is greatest in orchestral
works, where the range may be as much as 75 dB.
Vertically symmetrical driver array. Typically consists of a tweeter
mounted between two woofers. Creates a more-vertically directional
sound with evenly spaced lobes in the off-axis response when compared
with asymmetrical driver arrays.