Adventures In Audio
Classic Synthesizer: The Minimoog - VCO, VCF and VCA

David Mellor

David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Adventures In Audio.

Thursday January 1, 2004

The starting point for the sound themselves is obviously the Oscillator Bank. Some other synths of the time had only one or two oscillators, but the Minimoog has three and the difference is vast. Each oscillator can be set to ranges from a basso profundo 32' up to tin whistle 2'. The description as a certain number of feet corresponds to the way church organ pipes are labelled.

A pipe of 8' length for example will produce the note C two octaves below middle C on the piano. The overall tuning of the instrument, for which there is a knob in the 'Controllers' section, affects all three oscillators equally, but Oscillators 2 and 3 can have offsets applied which are normally used to thicken the sound up. Each oscillator can be set to one of six waveforms providing different amounts of high frequency harmonics. Oscillator 3 has an additional switch – info shortly.

Moving to the right, there is the Mixer section. On the original Minimoog this is rather awkwardly laid out since the two additional sound sources, the noise generator and the external source, are on the wrong side to make sense, and they split up the oscillators. Each source has not only an on/off switch but a level control so you can set the right blend.

The Modifier section is the heart and soul of the Minimoog. The upper modifier is the VCF (voltage controller amplifier) and the lower the VCA (voltage controller amplifier) and they both have envelope controls which respectively control the changes in timbre and level over time. Looking at the simpler VCA envelope generator we see that there are only three controls, for Attack, Decay and Sustain. Whatever happened to the Release parameter that other synths have? The answer is that there is an additional Decay switch next to the keyboard which can throw in a fixed amount of release. Not subtle exactly, but it seems to offer enough control, and anyway this is a classic instrument so we should be prepared to accept a few foibles.

On the top there is the cut off Frequency control which affects the brightness of the sound. At some stage or other you may have heard that the Moog filter used to be considered beyond compare in the world of synthesis. Let me tell you that it still is. The 24 decibel per octave slope gives it the cutting edge that other filters sadly lack even now. The Filter Emphasis Control performs the function that we would expect to be labelled 'Resonance' these days, and the Amount of Contour simply means how much effect the filter's three envelope controls have on the sound. From what you know now, you can get a massive variety of sounds, and there is still a whole lot more to come.

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