Through-Zero Frequency Modulation (TZFM) is a specific type of frequency modulation (FM) synthesis technique that allows for the modulation of an oscillator’s frequency both positively and negatively, effectively allowing the modulated oscillator to pass through zero frequency and continue into negative frequencies. This results in a more diverse range of timbres and harmonics when compared to traditional FM synthesis.
In typical FM synthesis, a modulator oscillator changes the frequency of a carrier oscillator, creating complex sidebands and new harmonics. However, when the modulation depth is high enough, it can cause the carrier frequency to approach or reach zero, resulting in the carrier oscillator stopping or producing unpredictable and less desirable timbres.
Through-Zero FM oscillators are designed to handle these situations more gracefully. As the carrier frequency approaches zero, the oscillator continues into negative frequencies, effectively inverting the waveform and producing more coherent and musically relevant sidebands and harmonics. This technique allows for a broader range of timbres and more precise control over the resulting sound.
See examples of TZFM oscillators on Modular Grid.