A brief Intro to Structured Audio
by John Lazzaro.
Structured Audio (SA) is a new file format,
that's part of the upcoming MPEG 4 Audio standard.
MP4-SA is different from other audio file formats,
like MP3 and RA and WAV, in a fundamental way:
Instead of describing the audio data
on the master tape, it describes the
music-making process -- the instruments
and effects and mixing console that
were used, the notes played, and the
slider and knob movements. It describes
these things in such a precise way,
that its possible to perfectly recreate
the audio by following the description.
What's the advantage to taking this approach?
Consider these scenarios:
[1] Musicians can collaborate on a performance
by passing around an MP4-SA file of the
work in progress. Different sequencer and
soft-synth programs will all be able to
read these MP4-SA files, and convert them
into audio that sounds identical to all
the collaborators (the power of an open
ISO standard, as compared to a closed format
controlled by a single company). A new part
gets added to the performance by adding to the MP4-SA
file -- adding new performance data as well
as new computer models of instruments and effects.
[2] You want to create a musical performance
as part of a video game, where the moods
of the characters modulate the music. Or
you want to create a stand-alone musical
performance, that downloads the current
weather from the web for the listeners
location, and modulates the music off this
data. Since the MP4-SA file describes the
music-making process, not the audio data,
these sorts of interactive performances are
possible. So are, incidently, non-musical
audio applications like audiology tests
over the Internet.
[3] You want to create a 1-minute performance
of interesting music with complex timbres,
that fits in a 3Kbyte file -- that's smaller
than the size of the M-station JPEG at the top
of this page! This is possible with MP4-SA,
if you make the right choices for instruments
and effects models, and if you use algorithmic
composition techniques.
Sound interesting? To be fair, MP4-SA is really
technology in progress -- its been recently
standardized by MPEG, under the leadership of
the MIT Media Lab's Eric Scheirer. But there
is free software available now to experiment
with MP4-SA, and musicians who feel comfortable
with simple computer programming can make
interesting music -- see what these musicians have
done with the tools, for example:
studio147.nl.eu.org/saol
To learn more about MP4-SA, and to download
software that runs under Linux (and to a
lesser extent, under Windows) to experiment
yourself, go here:
www.cs.berkeley.edu/~lazzaro/sa
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