[sdiy] Multiplier vs VCA?

[Scott Stites]

A multiplier is a device that multiplies one voltage times another.  The different types of multipliers are determined by what signs the two voltages can accomodate.  In other words, can you multiply a bipolar signal by another by bi-polar signal?  If so, that's a four quadrant multiplier, also known as a ring modulator.

Going through my own archives, I pulled a little bit of info out from the last time this subject came up.

Paul Perry furnished this information:

A one quadrant multiplier operates only on signals from say 0v to 10v
for both x and y.

A two quadrant multiplier works on signals of for example -10 to +10 for X, 
and 0 to +10 for Y.

And a 4 quadrant multiplier accepts inputs from for example -10 to +10 
both for x and for y.

Think of a graph with the x and y axis making four "quadrants",
the one quadrant multiplier works in the quadrant where all the voltages 
are positive, and so on.

And Ken Stone added:

Now for the really simple description

1 quadrant - VCA with half wave rectifier in front.
2 quadrant - VCA.
4 quadrant - Ring Modulator.

Cheers,
Scott


-----Original Message-----
From: synthplayer88 at spymac.com
Sent: Aug 18, 2004 12:51 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Multiplier vs VCA?


Hi guys,
I was wondering if anyone could help me out to clear my confusion on using a VCA
as a multiplier?

I was under the assumption that a VCA ultilize a voltage to control the output
amplitude eg.AM, whereas a multiplier ultilize a voltage to change the frequency
eg.FM. Which leads to my question which is how can you use a multiplier to as a VCA?

I know I must be missing something some where, thanks in advance.

BTW, has anyone done a meta list of VCA chips and multiplier chips?

Would love to know what's currently available out there to compare the functions
and the sounds?

Do they have actaully a "sound" of their own?

regards,
Scott


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