Effect of signal phase and masker separation on two-tone masking

The detectability of a sinusoid masked by two sinusoids was studied as a function of signal phase and the frequency separation between the two maskers. The signal frequency fs was equal to the arithmetic mean of the two masker frequencies, fl and fh, where fl less than fh. Signal frequencies of 1 and 4 kHz, eight signal phases, and 12 values of r = (fh-fl)/fs from 0.01-1.0 were used. The data could be divided into three regions. For large masker separations, r greater than 0.4, no consistent effects of signal phase were observed. For r less than 0.4, an effect of signal phase was evident at both signal frequencies. However, the effect of signal phase was different for the two regions 0.03 less than r less than 0.4 and r less than 0.03. For moderate masker separations, 0.03 less than r less than 0.4, masked thresholds were lowest at phases of 0 degrees and 180 degrees and highest at phases of 90 degrees and 270 degrees. For small masker separations, r less than 0.03, masked threshold was highest at 0 degree and the effect of signal phase depended on signal frequency. The different form of the phase effect for these three regions is discussed in terms of the use of different cues, arising from temporal resolution, spectral filtering, combination tones, and envelope spectra.