Multiplication in the time domain is the same as convolution in the frequency domain. Thus, in the basic case where two sine waves of frequencies *f _{1}* and

Interesting harmonics can be generated by carefully selecting and changing the frequency of the two input waveforms.

On the C64 SID chip, ring modulation multiplies a triangle wave with a square wave. A ring modulator was a common feature on early modular Moog synthesizers. The ring modulator went out of fashion with the advent of all-in-one synthesizers sampled-based synthesizers, but has returned as a feature in digital modelling and software synthesizers.