Editing Ring modulation (section)

==Integrated circuit methods of ring modulation==
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Some modern ring modulators are implemented using [[digital signal processing]] techniques by simply multiplying the time domain signals, producing a nearly-perfect signal output. [[Intermodulation]] products can be generated by carefully selecting and changing the [[frequency]] of the two input waveforms. If the signals are processed digitally, the frequency-domain convolution becomes [[circular convolution]]. If the signals are [[wideband]], this causes [[aliasing]] distortion, so it is common to [[oversample]] the operation or low-pass filter the signals prior to ring modulation.

The [[MOS Technology SID|SID]] chip found in the [[Commodore 64]] allows for [[triangle wave]]s to be ring modulated. Oscillator 1 gets modulated by oscillator 3's frequency, oscillator 2 by oscillator 1's frequency, and oscillator 3 by oscillator 2's frequency. Ring modulation is disabled unless the carrier oscillator is set to produce a triangle wave, but the modulating oscillator can be set to generate any of its available waveforms. However, no matter which waveform the modulating oscillator is using, the ring modulation always has the effect of modulating a triangle wave with a square wave.<ref>Commodore Programmer's Reference Guide, page 463</ref>{{not in ref|reason=Although the programming guide says that none of the parameters of the modulating oscillator affect the modulation, it does not state that a square wave is used|date=August 2021}}

On an [[ARP Odyssey]] synthesizer (and a few others from that era as well) the ring modulator is an [[XOR gate|XOR function]] (formed from [[XOR gate#Alternatives|four]] [[NAND gate]]s) fed from the square wave outputs of the two oscillators. For the limited case of square or pulse wave signals, this is identical to true ring modulation.

Analog multiplier ICs (such as those made by Analog Devices) would work as ring modulators, of course with regard to such matters as their operating limits and scale factors. Use of multiplier ICs means that the modulation products are largely confined to sum and difference frequency of inputs (unless the circuit is overdriven), rather than the much more complicated products of the rectifier circuit.