Book on

DAFX - Digital Audio Effects

Edited by Udo Zölzer
ISBN: 0-471-49078-4
John Wiley & Sons, 2002

Chapter 4

Modulators and Demodulators  

P. Dutilleux and U. Zölzer

Modulation is the process by which parameters of a sinusoidal signal (amplitude, frequency and phase) are modified or varied by an audio signal. In the field of audio processing modulation techniques are mainly used with very low frequency sinusoids. Especially the variation of control parameters for filters or delay lines can be regarded as an amplitude modulation or phase modulation of the audio signal. Wah-wah, phaser and tremolo are typical examples of amplitude modulation and vibrato, flanger and chorus are examples for phase modulations of the audio signal. For a deeper understanding of the possibilities of modulation techniques we will first introduce simple schemes for amplitude modulation, single side band modulation and phase modulation and point out their use for audio effects. The combination of these modulators will lead to more advanced digital audio effects, which will be demonstrated by several examples. In a further section we will describe several demodulators, which extract the incoming signal or parameters of the incoming signal for further effects processing.


Keywords: Modulation, Demodulation, Ring Modulator, Amplitude Modulator, Frequency Modulator, Detectors, Vibrato, Phaser, Morphing