Modulation refers to the process of using one signal to control, vary, or influence the parameters of another signal or module within the synthesizer. This process is at the core of modular synthesis and allows for the creation of complex, dynamic, and evolving sounds that would be difficult or impossible to achieve with static parameters.
In a modular synthesizer, modulation is typically achieved by using control voltage (CV) signals generated by various modules, such as LFOs (low-frequency oscillators), envelope generators, sequencers, or even audio-rate oscillators. These CV signals are then patched into the control voltage inputs of other modules to affect parameters like pitch, amplitude, filter cutoff, wave shape, and more.
Some common types of modulation in modular synthesis include:
- Amplitude modulation (AM): Using a control voltage signal to modulate the amplitude or volume of an audio signal, typically by controlling a voltage-controlled amplifier (VCA).
- Frequency modulation (FM): Using a control voltage signal to modulate the frequency or pitch of an oscillator, resulting in a wide range of harmonic and inharmonic sounds.
- Filter modulation: Using a control voltage signal to modulate the cutoff frequency or resonance of a filter, shaping the harmonic content and timbre of the input signal dynamically.
- Pulse-width modulation (PWM): Using a control voltage signal to modulate the width of a pulse wave, altering the harmonic content and creating unique timbres.
- Phase modulation (PM): Using a control voltage signal to modulate the phase of an oscillator or signal, resulting in complex waveforms and timbres.
Modular synthesizers are designed for extensive and flexible modulation possibilities, allowing users to connect and route signals in any configuration they choose, often leading to unexpected and creative results. This flexibility and exploration of signal routing and modulation are what make modular synthesis unique and powerful for sound design and electronic music production.