Phase offset modulation

Phase offset modulation

Phase offset modulation works by overlaying two instances of a periodic waveform on top of each other. (For the purposes of softsynths, the waveform is usually generated by using a lookup table.) The two instances of the waveform are kept slightly out of sync with each other, as one is furtherahead or further behind in its cycle. The values of both of thewaveforms are either multiplied together, or the value of one issubtracted from the other.

This generates an entirely new waveform with a drastically differentshape. For example, one ramp wave subtracted fromanother will create a pulse wave, with the amount of offset (iethe difference between the two waveforms' starting points) dictatingthe duty cycle. If you slowly change the offset amount, youcreate pulse-width modulation.

Using this technique, not only can a ramp wave create pulsewidthmodulation, but any other waveform can achieve a comparable effect.


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