ARP 2600 Ring Modulator Demo

video upload by O.Z. Hall

"This demo just scratches the surface of what you can do with a "Ring Modulator" (aka Balanced Modulator, aka 4 Quadrant multiplier).

Here is some technical detail ...
The term quadrant used below refers to cartesian coordinates ( e.g. x/y graph with 4 quadrants ).

Regarding two quadrant multipliers (e.g. VCA) versus four quadrant multipliers (e.g. Ring Modulator).
Here's a short definition;
A two quadrant multiplier will multiply two signals together
one (bipolar) input (the carrier) (e.g. VCA signal input - audio or a DC voltage - e.g. +/-5v )
another (unipolar ) input (the modulator) (e.g. a level control input, e.g. an envelope 0-5v ) .
A 4 quadrant multiplier will multiply two signals, both of which are bipolar.

The both multipliers create "sidebands", whose frequencies are the sum and difference of the two inputs. E.G. 100 Hz (carrier) and 25 Hz (modulator). The sideband frequencies are the sum (100+25 = 125 Hz) and the difference (100 - 25 = 75 Hz) .

A 2 quadrant multiplier is an unbalanced modulator while 4 quadrant multiplier is "balanced". This means that.
The VCA (unbalanced) would output the carrier and the sideband frequencies (100 Hz, 125 Hz, 75 Hz).
A ring modulator (balanced) outputs only the sideband frequencies (the carrier is suppressed)."