“AM” stands for Amplitude Modulation, which is a technique used to modulate the amplitude (volume) of a carrier waveform using a secondary modulator waveform. The amplitude of the carrier waveform is varied according to the amplitude of the modulator waveform, resulting in a new, more complex output waveform. This technique can be used to create a wide range of timbral effects, from subtle to highly dramatic, depending on the characteristics of the modulator and carrier waveforms.
Amplitude Modulation is typically achieved by using an oscillator or other signal source as the carrier and a second oscillator or control signal as the modulator. The modulator signal can be a low-frequency oscillator (LFO), an audio-rate oscillator, an envelope generator, or any other control signal. The choice of modulator waveform and its frequency will greatly influence the resulting sound.
When the modulator is an LFO, AM produces tremolo-like effects, where the volume of the carrier waveform fluctuates slowly over time. When the modulator is an audio-rate oscillator, more complex sidebands (additional frequencies) are introduced into the output signal, creating rich and evolving textures that can range from harmonic to inharmonic, depending on the relationship between the carrier and modulator frequencies.
Amplitude Modulation is a fundamental synthesis technique used in various types of synthesizers, including subtractive, additive, and frequency modulation (FM) synthesis. It provides a means to create dynamic and expressive sounds with evolving harmonic content.