ARTICLE  


[Part 2]

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.

A 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.

Marketing instrument-controlled 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

Looking at 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 figure 1.


INPUT SYSTEMS

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.

The voltage-controlled 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.

The Roland 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.

The 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."

The frequency 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.

The Musico 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.

Probably the 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.

The Resynator's 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.

[Continued...]
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