One of the more important synthesis techniques is modulation. Last semester we learned how to use an LFO to change the pitch of an oscillator slowly, creating vibrato. This week, we learn how to build that structure from the ground up using Max audio objects. The basic modulation scheme can be applied to any parameter, not just oscillator frequency. Any waveform, including band-limited noise (as generated by rand~), can act as a modulation source.
When one oscillator controls a parameter of another oscillator, we call the former a modulator and the latter a carrier. The carrier is the oscillator whose audio signal we hear; the modulator controls the behavior of the carrier.
If you raise the frequency of a periodic modulation source, such as a sine wave oscillator, so that it is higher than 20 Hz, you create timbral changes in the carrier oscillator. This technique of modulation synthesis comes in two basic forms: amplitude modulation (AM) and frequency modulation (FM), depending on whether the modulator) controls the amplitude or the frequency of the carrier.
We will try ring modulation (RM), which is a more commonly used special case of amplitude modulation. Then we will explore FM synthesis, which is more complex than either AM or RM.
Besides the value of exploring these two fundamental synthesis techniques, understanding modulation will help you produce more interesting time-varying sounds with whatever sound-producing method you’re working with. You might want to control the modulation parameters using real-time gestural input.