In the first
part of this article, we studied the structure of an instrument-
controlled synthesizer from the perspective of how a musical instrument
controls a set of synthesizer electronics. That was a general and
rather technical introduction to the subject. Now I would like to
turn to the subject of how the concepts turn into real products,
and how the products are marketed.
product is not just a system diagram. It has to interact with the
user, have certain standards of quality, and produce a pleasing
result. Out of the same system concepts could come a variety of
products in many forms, prices, levels of quality and sophistication.
At least three single-input instrument controlled synthesizers are
presently available, and each one represents a different approach
to product design. They differ in complexity, synthesis system features,
and price. I would like to explore these products to illustrate
the differing product philosophies now in practice.
synthesizers requires a thorough knowledge of the products, a carefully
contrived setup for demonstration, and the ability to teach the
musician a successful approach to instrument-controlled synthesis.
The musical instrument retailer always has a choice in the area
of marketing: to remain passive and somewhat ignorant, allowing
the musician to buy the product based on knowledge acquired elsewhere;
or to function as an educator and innovator, providing both the
environment and information necessary for the musician to understand
the product. With new and complex synthesis products, the retailer
can greatly accelerate the development of the market by providing
the latter situation.
DIFFERENT APPROACHES TO SYNTHESIS
the front panel controls of the three synthesizers in figure 1,
we can see that the control systems are both complex and different
from one another. We can compare them more easily if we break the
system down into their basic "building blocks," and then
compare each section separately. Remember that the control groups
on the panel reflect system components in the synthesizer, though
they may be arranged on the panel in unconventional ways. In figure
2, a system diagram for an instrument-controlled synthesizer is
presented, with special attention given to the control system components
that would appear on the panels. We can now take each section and
see what controls are associated with it on the three products in
The input section
links the musical input to the parameter extraction system. The
controls are set to provide the best "tracking" and response
to the input signal. The Resynator has a "sensitivity"
control and an "overload" light; the Roland SPV-355 has
a "threshold" control, a three position "instrument"
switch, and indicator lights; and the Korg X-911 has an "input
volume" control, "level" switch, "polarity"
switch, and two indicator lights. Do more controls indicate better
tracking or more versatility? Not necessarily. The final test is:
can you find a setting at which the synthesizer works optimally
with the instrument you are using.
oscillators are the primary tone-generators in the synthesizer.
The three synthesizers differ in many respects: number of VCO's
used, tuning controls, waveform outputs, special effects.
Korg has a
single VCO, with coarse and fine tuning controls and a hi-middle-lo
octave transpose switch. The VCO also has a portamento control.
The Korg derives many of its sounds by dividing the VCO by octaves
and processing the outputs.
synthesizer employs two VCO's, with a master tuning control, a three
position octave switch, and a portamento control. The oscillators
have three switchable waveforms. VCO 1 has a sub-octave divider
attached to it, whereas VCO 2 can be tuned to either of two switchable
intervals with respect to VCO 1.
Resynator also has two VCO's. The first VCO tracks the controlling
instruments, either in unison or with an octave up-or-down transposition.
The waveform is either a sawtooth, continuously variable pulse,
or modulated pulse by a variable frequency LFO (low frequency oscillator).
The second VCO, called FXO (effects oscillator) tracks the first
VCO at an interval determined by the front panel FXO tune control,
or at an interval "memorized" by the parameter extraction
system. The "memorized" interval can be changed by playing
a note and depressing a foot- switch, allowing for "real time"
trans- position of intervals (a patented feature) during live performance.
The FX O has three operating modes: free-running, "synced"
to VCO 1, or "complex modulation."
spectrum of the synthesized signal is controlled by the voltage-controlled
filter section. The filter is usually a lowpass type, with a cutoff
frequency control and a resonance control. The cutoff frequency
is often "tracked" to the note frequency for a consistent
tone quality, and is additionally controlled by an envelope generator.
In the Korg
synthesizer, the filter's audio input can be the input audio signal,
the signal from the voltage-controlled oscillator, or a distorted
version of the input signal. Instead of a continuously variable
resonance control, a three-position switch is used.
In the Roland
synthesizer, the VCO's provide the audio input to the filter, and
the resonance control is continuous. The "note" control
voltage as well as the "cutoff" control provide frequency
tracking for the filter.
synthesizer's filter tracks the VCO, and also has a cutoff frequency
control. The resonance control is continuously variable, but the
resonance control setting can be defeated by an external footswitch.
most important control voltage for the VCF is supplied by the envelope
generator assigned to the VCF. In the Korg synthesizer, an attack-decay
envelope generator, with variable attack and decay, times is pro-
vided. In the Roland synthesizer, an attack-decay-sustain envelope
generator or an envelope follower provides the filter control voltage.
The envelope control voltage may drive the filter either up or down
by means of a continuous control. The availability of an envelope
follower to control the filter provides a "dynamic" response,
following the loudness of the input signal.
VCF is controlled by an envelope generator called a Timeral Image
Modulator (TIM). The TIM pro- vides eight complex "shapes"
based on synthesized and acoustical instrument spectral envelopes.
A rate control com- presses or expands these shapes in time.
The VCA stage
in a modern synthesizer is often almost invisible from the front
panel. Its control source, the VCA envelope generator, usually contains
all the panel controls that affect the VCA. In an instrument-controlled
synthesizer, it is very desirable for the VCA to be related to the
loudness of the input signal. This provides additional dynamic expression
to parallel the expressiveness of the source instrument.
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