A modulator in regard to synthesis techniques is widely understood to be an audio-rate signal source that generates oscillations at frequencies within the range of human hearing (approximately 20 Hz to 20 kHz). When this audio-rate signal is used to modulate another audio signal or module parameter, it can create complex and harmonically rich timbres, as well as inharmonic, noisy, or dissonant sounds.
Common uses of audio-rate modulation in modular synthesis include:
- Frequency Modulation (FM): Modulating the frequency or pitch of an oscillator with an audio-rate signal, resulting in a wide range of harmonic and inharmonic sounds.
- Amplitude Modulation (AM): Using an audio-rate signal to modulate the amplitude or volume of another audio signal, often resulting in the creation of additional sidebands and more complex spectral content.
- Ring Modulation (RM): A type of amplitude modulation where two audio-rate signals are multiplied together, resulting in a new output signal with added sidebands and unique timbres.
- Waveshaping: Applying audio-rate modulation to waveshapers or wavefolders to dynamically alter the harmonic content of a signal.