Other Digital Audio Devices 625● Note that the MUSICAM algorithm is no longer used, it was developed into
MPEG-1 Audio Layers I and II. The name MUSICAM is a trademark used by
several companies.
● MPEG-1 is one of several (seven at the last count) MPEG standards, and we
seem to be in danger of being buried under the weight of standards at a time when
development is so rapid that each standard becomes out of date almost as soon as
it has been adopted. Think, for example, how soon NICAM has become upstaged
by digital TV sound.21.5 MP3 .......................................................................................................................
MP3 is a high-compression coding and decoding system that is now used for transmitting
audio signals over Internet links and for storing audio signals in compact computer fi le
form. MP3 allows the construction of small players that store, typically, 40 min of music,
but contain no moving parts. Because MP3 is a lossy form of compression, the MP3
deck for hi-fi systems has not emerged so far, but we should remember that the compact
cassette was also considered unfi t for hi-fi uses in its initial days. The Minidisk uses
similar compression methods.
The name MP3 began as an extension to a fi lename, devised to distinguish sound fi les
created using MPEG-1 Layer III encoding and decoding software. The PC type of
computer makes use of these extension letters, up to three of them, placed following a dot
and used to distinguish fi le types. For example, thoughts.txt would be a fi le called thoughts,
consisting purely of text, and thoughts.doc would be a document called thoughts, which
could contain illustrations and formatted text, even sounds. A fi le called thoughts.jpg
would be a compressed image fi le, and thoughts.bmp would be an uncompressed image
fi le. There are many such extensions, each used to identify a specifi c type of fi le.
The same MP3 extension is used for sound fi les that have used MPEG-2 Layer III with a
reduced sampling rate, but there is no connection between MP3 and MPEG-3. MP3 fi les
use a compression ratio of around 12:1, so that MP3 fi les stored on a recordable CD will
provide about 12 h of sound. See later for a description of DAM-CD.
The main use of MP3, however, has been the portable MP3 player, which allows MP3
fi les to be recorded from downloads over the Internet. This has made MP3 very much
of an audio system for the computer buff, but like all matters pertaining to computing,
this use is likely to spread. MP3 is unlikely to appeal to those who seek perfection in