Technical information

picture to the TV is therefore via either component video connections (in which
case, the TV reconstitutes the original RGB signal required for its CRT), or RGB (in
this case, the DVD reconstitutes the RGB signal).
Composite video This is the way that the three component video signals are
wrapped together to form a single signal, suitable for TV broadcast or carrying on
a single two-conductor cable. The two colour difference signals are first matrixed
together to form the chroma signal, and then the luminance signal is matrixed into
this to create a single composite video signal. This process results in some cross
interference between the chroma and luminance portions of the signal, reducing
picture quality.
Compression Reduction. Air is compressed by squeezing it into a smaller space.
Digital signals are compression by reducing the amount of data space required to
hold them. Some digital data compresses readily, due to easily identifiable
redundancy within the data. So, for example, a text document typically has a lot of
space characters and 'e' characters, so other ways of expressing these can be
found. Digital audio and video signal tend not to carry a lot of redundancy, so
systems that compress these highly rely on eliminating some of the data and are
consequently called lossy compression systems.
Compression driver A kind of loudspeaker driver. Rather than using a speaker
cone to directly vibrate the air in a room, a compression driver has a throat in
front of the moving part that causes a relatively small amount of air to compress
and rarify rapidly in response to the movement of that part. This, in turn, drives
the vibration of the air in front of it into the room, through some form of horn.
Most compression drivers use piezo effects for the initial vibration, although some
use more or less conventional cones. Compression drivers offer significantly
higher efficiency than conventional drivers, allowing high output levels for a given
input power, but can tend to reduce the dynamic range of the input signal and
colour the sound unless, well designed.
Compression ratio The extent to which a signal (particularly digital signals) is
compressed, expressed as a ratio of the uncompressed size to the compressed
size of the data. MP3, for example, with a bit rate of 128kb/s has a
compression ratio of about 11:1.
Constructive interference Where two signals, added together, act in sympathy
with each other to boost the signal level. For example, bass from a subwoofer
may, at certain frequencies, bounce from a nearby wall and that reflected signal
may interfere with bass still coming directly from the subwoofer to effectively
increase the output at that frequency. But it is also likely, at other frequencies, to
result in destructive interference.