Asymmetry of masking in the envelope-frequency domain

Abstract

Masked modulation thresholds can be influenced by the detection of amplitude fluctuations of the envelope (referred to as the venelope in the following) which arise from either beating between the masker modulation and the probe modulation, or from the intrinsic envelope fluctuations of a narrowband-noise modulator itself. It was tested to see to what extent the detection of venelope fluctuations is involved in corresponding tone-in-noise, noise-in-tone, and tone-in-tone modulation masking conditions. Modulation frequencies in the range from 20–100 Hz, applied to a 2.8-kHz sinusoidal carrier, were used. Thresholds in the noise-in-tone condition are always lower than those in the tone-in-noise condition, comparable with the asymmetry of the masking effect in the audio-frequency domain. In general, it was observed that (1) subjects use venelope fluctuations as a detection cue, and that (2) venelope fluctuations interfere with an additionally applied amplitude modulation when both fall into the same frequency range. To interpret the empirical findings, a general model structure for the processing of envelope and venelope fluctuations is proposed. Similarities between the auditory system’s coding strategies for audio frequencies/envelope fluctuations and envelope frequencies/venelope fluctuations are discussed.