Linear response VCA's

[Martin Czech]

> I've finally gotten my life in order to attack the modular synth project
> I've been promising myself for years.

I wish I could.

> Are there situations in which purely linear response is desirable in a VCA?

Yes, you can use a vca also for controling other modulations, e.g. an
automatic vibrato that comes on softly. In this case a linear response
sounds quite nice.  If you want to have some (deep) tremolo on audio
signals, it sounded better to me to use the linear input. Otherwise the
sine tremolo sounded uneven or strange.

Some time ago there was a discussion of envelope waveform, linear,
exponential etc. This makes a difference. If you want to hear it,
you'll also have to use the linear input.

In fact, the only application of expo control is slow fading with
linear control voltages, that's why devices like mixer vca have only
expo inputs.

I used SSM2018, this means you have to add a log circuit.  The expo
voltage and logged voltage are added Ve+log(Vl) and then feed to the
expo input exp{k(Ve+log(Vl))}= exp{k*Ve} * Vl^k.  There is some kind of
multiplication taking place between both inputs, this is a feature if
you use both at the same time, but it is also a bit confusing, if you
want full control scale of one input you have to turn the other to
100%. If you turn it to 0% instead, well this is even more complicated,
you need some rectifier to prevent the log cicuit going mad, etc.

Many people say that expo vcas sound punchier, well if you have a very
fast attack, the expo as well as the linear input look like a step,
maybe the difference is more in the medium attack range. The expo
control scale is a natural porperty of simple discrete multipliers, if
such are used, there may be audible control feedthrough, this can also
sound punchy.

If I where to have only one control input, I'd make them all linear.
An expo module can be added afterwards, if needed.

m.c.

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