Binaural perception of amplitude and frequency modulated signals

Abstract

The investigations focused on the binaural perception of amplitude modulated (AM) and frequency modulated (FM) signals. They are comprised of two experiments. In the first experiment binaurally perceived (matched) modulation depth for AM signals was determined under diotic conditions (i.e. for the same values of modulation depth coefficient, m, presented to the left (ml) and right (mr) ears) and under dichotic conditions (i.e. for different values of these coefficients ml[ampersand]ne;mr). The measurements were made for the interaural differences in modulation depth coefficient [ampersand]Delta;m, changing from 0 to 100% and a few selected modulating frequencies (4, 64 and 128 Hz) and carrier frequencies (250 and 1000 Hz). In the second experiment binaurally perceived (matched) frequency deviation of FM signals was determined under diotic conditions (i.e. for the same values of frequency deviation, [ampersand]Delta;f, presented to the left ([ampersand]Delta;f_l) and right ([ampersand]Delta;fr) ear ([ampersand]Delta;fl =[ampersand]Delta;fr) and under dichotic conditions (i.e. for different values of this deviation ([ampersand]Delta;fl[ampersand]ne;[ampersand]Delta;fr)). The measurements were made for the interaural differences of frequency deviation changing from 0 to 20 Hz; a few selected modulating frequencies (32, 64 and 128 Hz) and carrier frequencies (500 and 1000 Hz). It was found in Experiment I that for small interaural differences in modulation depth, [ampersand]Delta;m, the binaurally perceived modulation depth, m, is equal to the arithmetic mean of the depths presented to the left and right ears, whereas for large values of [ampersand]Delta;m, the value of m is smaller than the mean. The results of Experiment II revealed that the binaurally perceived frequency deviation is a linear function of interaural differences of this deviation and is equal to the arithmetic mean of deviations presented to the left and right ears.