Two-tone auditory spectral resolution.

Two component complex tones were synthesized so that each member of a complementary pair exhibited identical amplitude modulations; frequency modulations, however, were in opposite directions. Previous work has shown that the discriminability of the members of a complementary pair is related to the envelope-weighted differences in their instantaneous frequency functions. Listeners report that they base their discriminations upon differences in pitch between complementary two component signals. We assumed that the high discriminability found for moderate separations between the two component frequencies would not obtain if the components were resolved into separate critical bands. Thus we could define the just discriminable (75%) frequency separation as a direct estimate of spectral resolving power without recourse to assumptions about masking effectiveness, loudness summation, or other subjective changes thought to depend upon auditory spectral resolving power. Our findings indicate that resolution bandwidths resulting from the discriminability of complex tone pairs approximate the width of the traveling-wave envelope observed by von Békèsy. In light of our results, the implications for other critical bandwidth estimates are discussed.