Categories of Perception for Vibrato, Flange, and Stereo Chorus

Abstract

Vibrato, Flange, and Stereo Chorus are perhaps the three most often used digital audio effects that are created by smoothly modulating the duration of a delay line at typically sub-audio rates. Common practice is to use a periodic or quasi-periodic modulation control signal with frequency roughly between 2 and 9 Hz, and both the rate and depth of delay modulation are typically adjusted according to the aesthetic criteria of a performer or by an audio production engineer. In order to establish norms for the musically useful range of modulation rate and depth for such delay-based effects, 25 listeners were asked to make categorical judgments regarding their perception of vibrato, flange, and stereo chorus effects. The results map out for these two modulation parameters three perceptual regions for these three related effects: the region in which modulation is too subtle for effective use, the parameter ranges that seem most musically useful, and the region in which it is too extreme for most musical applications. Of particular interest is the observed commonality between these perceptual regions for vibrato, flange, and stereo chorus effects.