[sdiy] XOR as 'digital' ring modulator

[Magnus Danielson]

On 11/10/2010 09:27 PM, Tim Ressel wrote:
> As a hopefully interesting side note, there are 2 ways to obtain the  "ring
> modulator" function. The popular one for the synth crowd is a  linear multiplier
> like the AD633. The other way is by polarity reversal.  This is how true "ring
> modulators" work: the carrier signal goes  through an amplifier that has a
> selectable gain of + or - 1.  The  modulation signal's sign determines the gain
> polarity: when the mod  signal is positive the gain is +1, when negative, -1.
>
>
> This is of course not nearly as clean as the linear multiplier, but hey, clean
> is over-rated.
>
>
> The XOR ring mod works as a true ring mod, as an XOR gate is a
> digitally-controlled inverter.
>
> We return you now to your regularly scheduled programming.

No. The true ring mod does not have gain which shift between +1 and -1. 
It has a gain shifting between those two extremes. A true ring mod 
actually always have losses.

Modern ring-mod equivalents such as Gilbert cells can also be made to do 
4-quadrature multiplications like the old double-balanced diode rings.

Cheers,
Magnus