Technical information

considerable economies for long distance power transmission. Virtually all the
counties in the world use either a 50 or 60 hertz frequency for their power
systems. Europe, Australia and India use 50 hertz. The Americas and Japan use
60 hertz. See also DC.
AC-3 The encoding scheme used in Dolby Digital, the name by which it is now
more commonly known.
Acoustic suspension Also called infinite baffle. A design for the enclosure of a
loudspeaker. The enclosure is sealed so that it is air tight, which causes the air
within to become a very active part of the woofer's suspension. This raises the
resonant frequency of the driver and lowers its compliance. Acoustic suspension
speakers tend to be less efficient than bass reflex designs, and the bass notes
begin fading away at a higher frequency, but tend to be less than an equivalent
bass reflex speaker, so they frequently produce greater bass extension.
Active loudspeaker A loudspeaker with built-in amplification for all the drivers.
Some speakers have an amplifier built-in for bass only, but these are not regarded
as active. Most loudspeakers are passive, not active.
Active subwoofer Subwoofer with built-in amplification. Most subwoofers are
active, not passive.
ADC Analogue to Digital Converter. A component, circuit or device that converts
an analogue signal to a digital one, usually to some form of PCM. Compare DAC
which does the reverse.
AES/EBU Audio Engineering Society/European Broadcasting Union. A digital
audio communication standard most commonly seen in professional audio
applications. Electrically it is only subtly different to the consumer-oriented S/PDIF
standard, the main variation being a different method of handling the clocking
signal, and it generally being carried by balanced connections. Nevertheless
implementations are seen that seem to be fully compatible with unbalanced
S/PDIF.
AM Amplitude Modulation. A method of impressing a signal onto a sine wave for
its transmission or storage. A constant frequency sine wave has its amplitude
increased or decreased from moment to moment to correspond with the signal.
The sine wave, called a carrier, must be of considerably high frequency than any
component of the signal. AM radio is an application of this technique. Very
simple AM receivers (consisting of little other than a crystal and a coil) can be
implemented very easily to receive these signals, although of course more
sophisticated circuits can produce higher quality results.