DAB (digital audio broadcast) NRSC (National Radio
Systems Committee) term for the next generation of digital radio
DAC (or D/A,
digital-to-analog converter) The electronic component
which converts digital words into analog signals that can then
be amplified and used to drive loudspeakers, etc. The DAC is the
last link in the digital chain of signal processing
factor Damping is a measure of a power amplifierís
ability to control the back-emf
motion of the loudspeaker cone after the signal disappears. The
damping factor of a system is the ratio of the loudspeakerís nominal
impedance to the total impedance driving it. Perhaps an example
best illustrates this principle: letís say you have a speaker
cabinet nominally rated at 8-ohms, and you are driving it with
a power amp through 50 feet of 12 gauge cable. Checking the amplifier
data sheet, you donít find its output impedance, but you do find
that its damping factor is 300. What this means is that the ratio
of a nominal 8 ohm loudspeaker to the amplifierís output impedance
is 300. Doing the math [8 divided by 300] comes up with an amazing
.027 ohms! Pretty low. Looking up 12
gauge wire in your handy Belden Cable catalog tells you it has
.001588 ohms per foot, which sure ainít
much, but then again youíve got 100 feet of it (thatís right:
50 feet out and 50 feet back ó donít be tricked), so thatís 0.159
ohms. Which is about six times as much impedance
as your amplifier. (Now thereís a lesson in itself ó use
the correct †cable.) Adding these together gives
a total driving impedance of 0.186 ohms ó still pretty low ó yielding
a very good damping factor of 43 (anything over 10 is good enough,
so you donít have to get extreme about wire size).
DAR (digital audio radio) EIA term for the next generation of digital radio broadcasting
DASH (digital audio stationary head) A
family of formats for ensuring compatibility among digital multitrack
studio recorders using stationary (as opposed to rotating) heads.
The DASH standard, popularized by Sony
and Studer, specifies 2 to 48 tracks, with tape speeds from 12
to 76 cm/sec.
(digital audio tape recorder
) 1. A digital
audio recorder utilizing a magnetic tape cassette system with
rotary heads similar to that of a video recorder.
data compression See:
digital audio data compression
DAW (digital audio workstation)
Any of several software/hardware systems using a computer
as the basis for creating, editing, storing, and playback of digital
audio, using the computer's hard disk as the recording medium.
DB-25 connector A 25-pin D-shell
connector standardized for RS-232 serial
DB-9 connector A smaller 9-pin version of the connector
used for RS-232 communications. First made popular by IBM in their
AT personal computer.
(Digital Compact Cassette) Philips's digital version
of the standard analog cassette tape system. A DCC recorder plays
and records digital cassettes, as well as playing analog cassettes.
DCE (Data Communications Equipment)
Within the RS-232 standard, the
equipment that provides the functions required to establish, maintain,
and terminate a connection, as well as the signal conversion,
and coding required for communication between data terminal equipment
and data circuit - e.g., a modem or printer. See:
The main difference between DCE and DTE is the wiring of pins
2 and 3, thus the need for a null modem cable when tying two computers together.
decibel Abbr. dB Equal to one-tenth
of a bel. [After Alexander
Graham Bell.] The preferred method
and term for representing the ratio of different audio
levels. It is a mathematical shorthand that uses logarithms
(a shortcut using the powers of 10 to represent the actual number)
to reduce the size of the number. For example, instead of saying
the dynamic range is 32,000 to 1, we say it is 90 dB [the answer
in dB equals 20 log x/y, where x and y are the different signal
levels]. Being a ratio, decibels have no units. Everything
is relative. Since it is relative, then it must be relative to
some 0 dB reference point. To distinguish between reference
points a suffix letter is added as follows:
dBu A voltage reference point equal to 0.775 Vrms
. [This reference originally was labelled dBv (lower-case)
but was too often confused with dBV (upper-case),
so it was changed to dBu (for unterminated).]
Standard pro audio voltage reference level equal to 1.23 Vrms.
A voltage reference point equal to 1.0 Vrms.
Standard voltage reference level for consumer and some pro audio
use (e.g. TASCAM), equal to 0.316 Vrms.
(Tip: RCA connectors are a good indicator of units operating at
-10 dBV levels.)
A power reference point equal to 1 milliwatt.
To convert into an equivalent voltage level, the impedance
must be specified. For example, 0 dBm
into 600 ohms gives an equivalent voltage level of 0.775 V, or
0 dBu (see above); however, 0 dBm
into 50 ohms, for instance, yields an equivalent voltage of 0.224
V -- something quite different. Since modern audio engineering
is concerned with voltage levels, as opposed to power levels,
the convention of using a reference level of 0 dBm
is obsolete. The reference levels of 0 dBu, or -10 dBV are the preferred units.
0 dBFS A reference level
equal to "Full Scale." Used in specifying A/D and D/A audio data converters. Full scale refers to the maximum voltage
level possible before "digital clipping," or digital
overload of the data converter. See:
Full Scale value is fixed by the internal data converter design,
and varies from model to model.
de-esser A special type of audio signal compressor
that operates only at high frequencies (>3 kHz), used to reduce
the effect of vocal
delay Related to a signal that has been delayed in time in
reference to it origination. May refer to any of the
following: 1. A signal processing device or circuit used to delay
one or more signals by a controllable amount of time. This
feature is used to correct for loudspeaker drivers that are mounted
such that their points of apparent sound origin (not necessarily
their voice coils) are not physically aligned. Good delay circuits
are frequency independent, meaning the specified delay is equal
for all audio frequencies (constant group delay). Delay circuits
based on digital sampling techniques are inherently frequency
independent and thus preferred. 2.
MI. Digital audio delay circuits comprise
the heart of most all "effects'' boxes sold in the MI world.
echoing, looping, etc., all use delay in one form or another and
are therefore some times referred to as Delays.
3. Sound Reinforcement. Acousticians and sound contractors
use signal delay units to "aim" loudspeaker arrays.
Introducing small amounts of delay between identical, closely-mounted
drivers, fed from the same source, controls the direction of the
4 Slight delay that sometimes occurs when transferring video,
audio and data signals over long distances. When offensive, may be
corrected using a digital echo canceling circuit.
DHCP (Dynamic Host Configuration Protocol)
- Servers that permit multiple devices to share a limited group of
IP addresses by assigning and reserving a temporary address form
the pool of addresses to a device as needed.
Digital A device, process or protocol based on
digitization of information to enable storage,
transportation or processing.
digital audio data compression
Any of several algorithms
designed to reduce the number of bits (hence, bandwidth and storage
requirements) required for accurate digital audio storage and
transmission. Characterized by being "lossless" or "lossy." The audio compression is "lossy" if actual data is lost due to the compression
scheme, and "lossless" if it is not. Well designed algorithms
ensure "lost" information is inaudible.
digital audio The
use of sampling and quantization techniques to store or transmit
audio information in binary form. The use of numbers
(typically binary) to represent audio signals.
digital filter Any filter accomplished in the digital domain.
digital signal Any
signal which is quantized (i.e., limited to a distinct set of
values) into digital words at discrete points in time. The accuracy
of a digital value is dependent on the number of bits used to
conversion of analog information into a digital form.
DIN Acronym for Deutsche Industrie Norm (Deutsches Institut fur Normung), the German
standardization body. Often used to describe
Diode A two terminal electronic
device that will pass reasonably unimpaired electrical current in
one direction but provide a high degree of resistance to current
flow in the other direction. Diodes are often found in
Rectifier (converts AC current to intermittent DC current)
disc The term used for any optical storage media.
Originally popularized to refer to phonograph records. From
Latin discus, the term refers primarily to audio and
video storage systems, such as compact discs, laser discs,
etc., but the advent of CD-ROMs and computer optical storage units
blurs this distinction. Compare with
a separate thing; distinct, or a set of distinct things.
discrete Fourier transform (DFT) 1. A numerical method of calculating the coefficients of the
Fourier series from a sampled periodic
signal. 2. A
used to determine the Fourier coefficient corresponding to a set
of frequencies, normally linearly spaced. See:
disk The term used for any magnetic storage media
such as computer diskettes or hard disks. From Greek diskos,
the term refers primarily to non-audio digital data storage,
but the advent of hard disk digital audio recording systems fogs
this up somewhat. Compare with
Distortion any departure
of the output signal
waveform from that which should result from the input signal
waveform's Distortion may result from many mechanisms,
including nonlinearities in active and passive components.
distribution amplifier A
splitter with buffer amps on each output.
dither The noise (analog or digital) added to a signal prior to
quantization (or word length reduction)
which reduces the distortion and noise modulation resulting from
the quantization process. Although there is a slight increase
in the noise level, spectrally shaped dither can minimize the
apparent increase. The noise is less objectionable than the distortion,
and allows low-level signals to be heard more clearly.
Acronym for do-it-yourself, usually referring to various
hobbies, especially audio-related.
Dolby's name for its format for the digital
soundtrack system for motion picture playback.
C-3system of digital compression.
The signal is optically printed between the sprocket holes.
Now being introduced to Home Theater on laser disc and DVD.
Dolby Digital may use any number of primary audio delivery and
reproduction channels, from 1 to 5, and may include a separate
bass-only effects channel. The designation "5.1" describes
the complete channel format. Surround decoder systems with Dolby
Digital automatically contain Dolby Pro Logic processing to ensure
full compatibility with the many existing program soundtracks
made with Dolby Surround encoding.
"doss") (disk operating system) A
software program controlling data in memory, disk storage, running
programs and I/O management.
downward expander See:
error condition in which of a signal are incorrect or lost from
a digital medium. Occurs with digital and analog - audio or video.
(Direct Stream Digitalô) Joint trademark of Sony
and Philips for their "Super Audio CD" proposal for
the next generation CD-standard. Sony and Philips
have split form the
DVD ranks to jointly propose their own
solution comprised of a 1-bit, 64-times oversampled
direct-stream digital Super Audio CD format. The Super Audio CD
is a hybrid disc comprising two layers: a high density (HD) DSD
layer in the middle, and a standard density CD layer at the bottom.
The two layers are read from the same side of the disc; the CD
laser reads the bottom reflective layer through the semi-transmissive
HD layer, while the middle layer is read by the HD laser delivering
high-quality, multichannel sound without
sacrificing backward compatibility. The HD layer has three tracks:
The innermost is for two-channel stereo; the middle is a six-channel
mix; and the outer is for such additional infomation
as liner notes, still images and videro
clips. Maximum playing time is 74 minutes.
(Digital subscriber Line) Command
"Last Mile" technology used to piggyback reasonably high speed
data services over standard twisted copper telephone (POTs) lines
between the telephone switching station and individual users
DSP (digital signal
processing) A technology for signal processing that combines
algorithms and fast number-crunching digital
hardware, and is capable of high-performance and flexibility.
DTE (Data Terminal Equipment) Within the
the equipment comprising the data source, the receiver, or both
- e.g., personal computers or terminals. See:
DCE. The main
difference between DTE and DCE is the wiring of pins 2 and 3,
thus the need for a
null modem cable
when tying two computers together.
dynamic processor that lowers (or "ducks") the level
of one audio signal based upon the level of a second audio signal.
A typical application is paging: A ducker senses the presence
of audio from a paging microphone and triggers a reduction in
the output level of the main audio signal for the duration of
the page signal. It restores the original level once the page
message is over.
to a simultaneous two-way independent transmission in both directions.
This may be accomplished with two channels, one in each direction,
or in digital circuits by time sharing a single channel. Often referred to as "full duplex" which is redundant.
DVD (latest info says
"DVD" no longer stands for anything! It used to mean
"digital versatile disc" - and before that it meant "digital video
disc") A new type of 12-centimeter (4.72") compact disc (same
size as audio CDs and CD-ROMs) that holds 10 times the information.
Capable of holding full-length movies and a video game
based on the movie, or a movie and its soundtrack, or two
versions of the same movie - all in sophisticated discrete digital
audio surround sound. The DVD standard specifies a laminated single-sided,
single-layer disc holding 4.7 gigabytes, and 133 minutes of MPEG-2
compressed video and audio. It is backwards compatible, and expandable
to two-layers holding 8.5 gigabytes. Ultimately two discs could
be bounded together yielding two-sides, each with two-layers,
for a total of 17 gigabytes. There are four versions: DVD-Video
(movies), DVD-Audio (music-only), DVD-ROM and DVD-RAM (games and
computer use). The DVD-Audio standard is still being defined.
DVI (Digital Visual Interface) A recent
connection standard for linking a computer video card to desktop,
projection or wall mounted displays using a digital signal.
Also defines a standard 24 pin connector for DVI connections.
DWDM ( dense wavelength-division
multiplexing ) A technology that puts data from different
sources together on a single
with each signal carried at the same time on its own separate
Using DWDM, up to 80 (and theoretically more) separate wavelengths
channels of data can be multiplexed into a
lightstream transmitted on a single optical fiber. Each channel
carries a time division multiplexed (TDM)
signal. In a system with each channel carrying 2.5
Gbps (billion bits
per second), up to 200 billion bits can be delivered a second by
the optical fiber. DWDM is also sometimes called wave division
dynamic controllers (or
processors) A class of signal processing devices used to alter
an audio signal based solely upon its frequency content and
amplitude level, thus the term "dynamic" since
the processing is completely program dependent. The two most common
dynamic effects are
(or just "gates"),
being subsets of these. Another dynamic controller category includes
dynamic microphone A microphone design where a wire coil (the voice coil) is attached
to a small diaphragm such that sound pressure causes the coil
to move in a magnetic field, thus creating an electrical voltage
proportional to the sound pressure. Works in almost the exact
opposite of a dynamic loudspeaker where an electrical voltage
is applied to the voice coil attached to a large cone (diaphragm)
causing it to move in a magnetic field, thus creating a change
in the immediate sound pressure. In fact, under the right circumstances,
both elements will operate as the other, i.e., a dynamic loudspeaker
will act as a microphone and a dynamic microphone will act as
a loudspeaker -- although not too loud.
dynamic range The ratio of the loudest (undistorted)
signal to that of the quietest discernible (often the system noise
level) signal in a unit or system as expressed in
(dB). Dynamic range is another way of stating the maximum
With reference to signal processing equipment, the maximum output
signal is restricted by the size of the power supplies, i.e.,
it cannot swing more voltage than is available. While the minimum
output signal is determined by the noise floor of the unit, i.e.,
it cannot put out a discernible signal smaller than the noise.
Professional-grade analog signal processing equipment can output
maximum levels of +26 dBu, with the
best noise floors being down around -94 dBu.
This gives a maximum dynamic range of 120 dB - pretty impres/sive
numbers, which coincide nicely with the 120 dB dynamic range of
normal human hearing (from just audible to uncomfortably loud).
dyne A unit of force, equal to the force required to impart an
acceleration of one centimeter per second per second to a mass
of one gram. Used to Define dB-SPL