ANALYTICAL EXPRESSIONS FOR THE ENVELOPE CORRELATION OF NARROW-BAND STIMULI USED IN CMR AND BMLD RESEARCH

Analytical solutions are presented for the correlation between the env elopes of certain narrow-band stimuli that are typically used in exper iments on binaural unmasking and on Comodulation Masking Release (CMR) . These stimuli consist of two maskers with identical envelopes and a signal that is added to one of the maskers. If the two maskers have th e same center frequency and are presented to the right and left ear, t he stimulus resembles a binaural MoSm condition. If the two maskers ha ve different center frequencies, we have a CMR condition with one flan king band. The solutions for the envelope correlation differ depending on whether the envelope correlation is expressed as normalized cross correlation or as normalized cross covariance (Pearson product-moment correlation). The envelope correlation depends on the statistics of th e masker and the signal whereas the waveform correlation depends on ne ither. This influence only disappears for the normalized envelope cros s correlation provided that the masker level is much higher than the s ignal level. In this case the envelope cross correlation is approximat ely equal to the square root of the waveform correlation. It is argued that the different properties of both types of envelope correlation a re of relevance for CMR research. (C) 1998 Acoustical Society of Ameri ca.