Harmonics refer to the frequencies that are multiples of the fundamental frequency of a sound. The fundamental frequency is the lowest frequency that is present in a sound, and harmonics are integer multiples of the fundamental frequency.
For example, if a sound has a fundamental frequency of 100 Hz, the first harmonic would be 200 Hz (2 times the fundamental frequency), the second harmonic would be 300 Hz (3 times the fundamental frequency), and so on.
Harmonics play an important role in shaping the timbre or tonal quality of a sound. The presence and relative strength of harmonics determine the overall character of a sound, whether it is a bright, metallic sound with many high-frequency harmonics, or a warm, mellow sound with more emphasis on lower-frequency harmonics.
In a modular system, harmonics can be created and manipulated in various ways. Oscillators can generate complex waveforms that contain many harmonics, and the relative strength of these harmonics can be adjusted using filters, envelopes, and other modules. Filters can be used to emphasize or attenuate specific harmonics, while envelopes can be used to shape the strength of harmonics over time.
Harmonic distortion is another technique used in modular synthesis to add harmonics to a sound. This can be achieved through the use of dedicated distortion modules or by overdriving certain modules in a signal chain. Harmonic distortion can add warmth, grit, and character to a sound, and can be used to create a range of musical effects, from subtle distortion to extreme distortion.