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Tuesday, April 24th, 2018 08:03 pm

Synth Glossary

An envelope generator generates a signal that changes through the length of a sound, normally to control the loudness of that sound. An example of its use is to control the volume of a piano sound. It creates a signal that goes from low to high very quickly (the loud bit when the key is pressed), then goes down slowly as the sounds gets quieter. They are also used to drive other parts of the synthesizer, for example the filter....


"The Prophet 5 contains five individual voices. For its principal sound sources each voice contains two VCO's (voltage controlled oscillators), OSC A and OSC B, and a white noise source which can be mixed into a resonant low-pass VCF (voltage controlled filter). The filter modifies the voice timbre under control of its four-stage envelope generator. The filter may also be resonated and serve as a sound source. Following each filter, a VCA (voltage controlled amplifier), also controlled by a four-stage envelope generator, shapes the voice amplitude. Supplementing the basic voices are polyphonic modulation (POLY-MOD) signal routings within each voice that allow OSC B and the filter envelope generator to function as modulation sources applied to OSC A frequency or pulse width, or the filter frequency. Finally, there is a single LFO (low-frequency oscillator) and a pink noise source which can be mixed to modulate all five voices, as adjusted by the MOD wheel.

"The Prophet-5 sustained six revisions (or revs). Rev 1 was the original design. Rev 2 was a refinement of the original design and largely transparent. Rev 3, however, was a vastly different synthesizer than Revs 1 and 2. Introduced to Rev 3 were new voltage controlled IC's (CEM), an improved ADC, DAC, and a different control voltage distribution scheme. More sophisticated editing and tuning routines were designed, and to improve servicibility, voice trimmers were reduced from 80 to 45. Some believe that the Rev 3 synthesizers are slightly inferior (sonically) to their predecessors by revealing an absence in the lower frequencies. While this may be true, the majority of the Rev 3 synthesizers are far more operationally stable than their Rev 1 and Rev 2 counterparts.

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