Technical information

matrixed into two channels. The Dolby Surround decoder extracts the additional
channel, known as the surround channel, and sends it to a pair of rear or
surround speakers. This surround channel is limited in frequency range to 100-
7,000 hertz.
Driver The moving part, or parts, of a loudspeaker. These are usually woofers
(bass drivers), midrange drivers and tweeters (high frequencies). There are a
number of different driver designs. Virtually all woofers use the traditional speaker
cone (some light material, often paper pulp or polypropylene) held in place by a
suspension and backed by a coil inserted into the magnetic field of a strong
permanent magnet. The amplifier's signal is fed into the coil, generating its own
magnetic field, causing the coil and the attached cone to move. Midrange drivers,
which are relatively rare these days, usually use either cones or domes (often
polypropylene or a light metal such as magnesium), although there are some
ribbon midrange drivers. Tweeters are most commonly domes (often
polypropylene, silk or some other textile, or a light metal such as aluminium or
titanium), but cheaper ones use cones. Some use inverted domes (that is, they
are concave rather than convex), while some expensive speakers use ribbon
tweeters. There was even, for a while, a 'plasma' tweeter where the high
frequencies were generated by a pulsating ball of superheated air. Some
speakers do not use what could be conventionally called drivers, for example
electrostatic speakers.
DRC Dynamic Range Control. See Dynamic Range Control.
DRM Digital Rights Management. A catch-all name for various systems that
control the distribution of digital audio and video content. Usually based on
secure(-ish) keys and encryption.
DSD Direct Stream Digital. The digital audio format used in the SACD. Unlike the
PCM system normally used, DSD uses a stream of single bits of information. The
momentary level of the analogue wave form being represented by the bitstream is
determined by the density with which the bits are 'on' rather than 'off'. It is
modified by using noise shaping to increase the effective dynamic range in the
main audible band. DSD uses for each channel a bit rate of 2,822,400 bits per
second.
DSP Digital Signal Processor. A computer-type processing unit optimised to
perform 24 or 32 bit floating-point operations on digital audio signals. This allows
it to perform Fast Fourier Transforms and other complicated operations in real-
time to apply frequency response adjustments, generate reverberation and even
split-out certain frequency bands into separate channels. Many home theatre