Re: [sdiy] Multiplier vs VCA?

[Roman]

>Right, so if I understand this correctly.
>A VCA will only accept 1 input with AC signal and the other must be DC voltage

every multiplier accepts DC, it's the surrounding circuitry (caps) that limit it to AC. So any input can be used from DC to several MHz sometimes.

>either +ve or -ve, which makes an audio expander or compressor if the DC voltages
>are generated from a logrithmic function? 

it's a bit longer way from VCA to expander/compressor. You would first need to measure amplitude of input signal and based on that change control voltage of the VCA. If you put reversing attenuator before VCA input, you will get plain amplifier in the middle pot position, expander in positive half of the pot, and compressor in negative half.
Logarithmic function doesn't change much, or I don't understand the question well


>Isn't there a VCA chip that can take both +ve DC and -ve DC to be ultilised both
>as a compressor and expander know as compunder? or would you need 2 seperate VCAs
>one takes +ve input and the other -ve to achieve both compressing and expansion
>seperately?

I think I answered it above. One common VCA is enough, but ou need to add some controll circuitry. Not much, but still.


>A multiplier can take AC signal from both inputs and multiply both input voltage
>as the outcome which explains the sound of the ring modulator, creates bursts of
>explosions in amplitude?

yes. Mutliplier will take input spectrum of one signal and shift it up and down in reverse by the frequency of sine signal on second input. If that signal is more complicated than sine, the output will be summ of all "up" and "reverse down" images shifted by the frequency of all spectrum components of the second signal. So multiplying 2 rich-in-spectrum signals would give thousands of frequecy components at the output.
Well, I wrote it in a way I barely understand it myself, but it's really simple.

Roman