Could
cellular automata be the hi-fi enthusiast's new best friend? Is it time
to say MP3 is out? A new lossless compression system for digital audio files is on the horizon
thanks to work by Japanese physicists working with the rules of cellular
automata.
If you are a music fan with a computer then chances are you have
come across the MP3 format for compressing digital sounds using a Fourier
transform. A five-minute song, which would take up 55 megabytes of space
on a compact disk is squashed down to just five megabytes or so in the MP3
format. The format uses a computer algorithm to strip out data from the
original sound file that would not normally be heard on all but the
highest of hi-fi music systems.
However, the MP3 approach is not perfect. Because it strips out
some of the audio data from the sound file, it is said to be a 'lossy'
system because there is a loss of information and so aural quality. Hi-fi
enthusiasts and scientists who work with sound files in their research
would much prefer a 'lossless' compression system.
Writing in Phys Lett A, recently Masato Wada and
Jousuke Kuroiwa of Hiroshima University, and Shigetoshi Nara of Okayama
University, Japan describe how they have devised a simple rules system
that allows an audio file, whether spoken word or music, to be compressed
using the
dynamics rules
of cellular automata. The process developed by the Japanese team can be
used to reproduce completely the sound using only two rules in
one-dimensional cellular automata with no loss of information.
According to
Kuroiwa and colleagues chaotic phenomena have become increasingly well
understood. But, complex systems with large but finite degrees of freedom
- the sound of a symphony, a heated debate or a searing guitar solo, for
instance, are less easy to define. However, rule dynamics, the team
believes could be used to generate a large complex system using. So, just
as fractal visual patterns that look like the repeating fronds of a fern
or the valleys and peaks of a mountain-scape can be generated with a
simple set of rules repeatedly applied so too might a set of rules be used
to define the sequence of frequencies and amplitudes that make up a sound.
The team has now defined a set of rules based on the rule dynamics of one-dimensional cellular automata.
The cellular automata have two states and three neighbors so are described as "1-2-3 CA".
Possible scientific applications of the reproducible compression
approach might be in spotting characteristic features of a digital sound
or evaluating complexity of given data in the sense of Kolmogorov
complexity. However, the compression of sound could ultimately have a more
popular appeal for the wide dissemination of audio for entertainment
purposes too. Listen carefully.