of Microprocessors

SOME REAL ApPLICATIONS 729
copying, in fact, occurs whenever a patch is selected in the program select
mode and also includes "expanding" the compressed format used to conserve
space in the CMOS memory into a format the control program can
manipulate easily.
All-Digital Synthesizers
The previous section described what is essentially the epitome ofanalog
synthesizer design. Of course, mote basic waveshapes, filter modes, patching
flexibility, and voice boards could be designed in to make a bigger
instrument, but not really a different one. In the extremely competitive
synthesizer world, as soon as one instrument design is complete and in
production, work begins on a new design. Since instruments like the Chroma
have taken analog sound generation technology about as far as it can go, real
innovations must be in other areas. In the context of a hybrid instrument,
most of the activity has been in more powerful control programs and more
informative control panels. For example, many more software-generated
envelopes and low-frequency modulator oscillators have been included in
recent designs. Numeric readouts are being replaced by alphanumeric and
even limited graphics displays to allow effective communication with the
more complex control programs.
To come up with something truly new in a live performance synthesizer,
it is becoming necessary to use digital synthesis techniques for the
soun'd waveforms themselves as well as the envelope shapes. Of course, one
immediate advantage of digital synthesis is its inherent accuracy. While
automatic tuning is effective (provided it is performed about twice an hour
and the room temperature is reasonably stable), it is not needed at all in a
digital instrument. Also, factory adjustments, which must be touched up
after a few years or when components are replaced, are not needed either.
Finally, some synthesis algorithms, such as FM with reflected harmonic
sidebands, are much more predictable when frequency uncertainties are zero.
The biggest advantage of digital, however, is that the whole spectrum
of synthesis techniques is available. It should not be a surprise that the
synthesis technique an instrument uses affects how the user "thinks about"
sound. Whereas analog synthesis is virtually synonymous with subtractive
(filter) synthesis, a digital system can be based on additive (harmonic),
frequency modulation, nonlinear, direct waveshaping, or even VOSIM
synthesis techniques. Besides these synthesis-from-scratch methods, modification
techniques such as frequency shifting, dispersion, arbitrary filtering,
envelope modification, and others are potentially available. Finally, an
endless variety of parameter transferral, record-playback, and analysissynthesis
techniques are possible. No instrument uses all or even most of
these possibilities, but they do provide a rich source of ideas for instrument
designers.