Technical information

into account the impedance of the wiring between amplifier and loudspeakers, nor
the impedance of the speakers' own voice coils. Consequently there is only a
modest performance gain between a damping factor of, say, 60 and one of 600.
DAT Digital Audio Tape. A compact tape developed in the late 1980s by Sony
which stores audio in PCM format. The tapes look very similar to the MiniDV
tapes used in digital video cameras, but are somewhat larger, measuring 71mm
wide by 53mm deep and 10mm thick. The default format for DAT is a 48 kHz
sampling frequency and 16 bits of resolution, but they can also be switched to
44.1kHz.
dB Decibel. See decibel.
dBFS Decibel - Full Scale. The level of a signal, measured in decibels, with
reference to the maximum possible level of the signal. With digital audio the
maximum recording level is 0dBFS, so all measurements of the signal are negative
values.
dBSPL Decibel - Sound Pressure Level. A measure of sound intensity. This is a
logarithmic measure. To increase the sound level by three decibels, it is
necessary to double the power output. A 10dB increase in sound level roughly
equates with a perceived doubling of volume level. A figure of around 120-130dB
is normally considered to be the threshold of pain. dB is sometimes loosely used
as a synonym.
DC Direct Current. An electric current that retains its level and direction, at least
in the short term. More generally, DC is also used to describe voltage sources
that deliver this kind of current. DC is generally used at low voltages within
electronic equipment. Batteries deliver DC. Compare with AC.
DCC Digital compact cassette. An attempted replacement for the compact
cassette introduced by Philips in the late 1980s, early 1990s. This recorded
audio in digital format, but used a lossy compression system. It failed to make
headway since Sony's Minidisc had the advantage of direct access. More
recently, the recordable CD and DVD provides convenient and cheap recording
with higher quality.
Decibel Abbreviation dB. A logarithmic measure of ratio. To determine the
decibel relationship of, for example, two voltages you use the formula
dB=20*log(V1/V2). If the result is negative, V1 is less than V2. If positive, then
V1 is greater than V2. For power the formula is dB=10*log(P1/P2). dB is often
used loosely as shorthand for dBSPL.