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Another advantage of the fractal method is scalability. Because patterns
— rather than pixels — are viewed as the fundamental blocks of image con-
struction, the fractal algorithm can fill in missing detail during decompres-
sion by mathematically scaling the pattern instead of just inserting extra
pixels. This results in a higher degree of accuracy for decompressed
images, which may be very important in multimedia, engineering, and
design applications.
Audio Compression
Audio files are used over the Internet in a variety of ways. Radio stations
have set up Web sites to allow access to program archives. Music compa-
nies publish selections from new CDs to encourage sales. Many instructors
tape their lessons and post the audio files on the Web as part of the learn-
ing at a distance program at their college. Corporations are starting to put
the contents of executive speeches and annual meetings on their Web sites.
In addition, audio files can be created by sound recorders on PCs for trans-
mission over the Internet as voice mail messages.
There are several algorithms in use that compress audio files and
employ optimization techniques to ensure efficient delivery over the Inter-
net. Among the noteworthy voice compression algorithms in popular use
today are GSM and TrueSpeech.
GSM is the global system for mobile telecommunication and is a world-
wide standard for digital cellular communications. It provides close to a 5 to
1 compression of raw audio with an acceptable loss of audio quality upon
decompression. Although the GSM codec was originally developed for real-
time conversations by cell phone, it has been adapted for several other
uses, including Internet telephony, audio file distribution, and voice mail.
TrueSpeech is a product of The DSP Group, Inc. It can provide upward of
18 to 1 compression of raw audio with an imperceptable loss of audio qual-
ity on decompression. Offering a high compression ratio, TrueSpeech is
more CPU-intensive than GSM, so it requires a faster processor to com-
press the same amount of audio in real time. Like GSM, TrueSpeech is used
for Internet telephony, audio file distribution, and voice mail.
The G.723.1 voice codec is based in large part on The DSP Group's
TrueSpeech. G.723.1, which combines low bit-rate compression with toll-
quality communications at highly compressed rates of 6.3 and 5.3K bps, was
developed for videophone and videoconferencing applications over public
switched telephone networks, and adopted by the International Telecom-
munications Union (ITU) in 1995. By way of G.723.1, TrueSpeech is also
found in the ITU H.324 standard for video telephony over ordinary tele-
phone networks as well as the ITU H.323 standard for videoconferencing.
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