ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

3aPP7. Mixed modulation masking: AM masking FM and FM masking AM.

Brent W. Edwards

Neal F. Viemeister

Dept. of Psych., Univ. of Minnesota, Minneapolis, MN 55455

In a series of experiments, the masking of AM by FM and the masking of FM by AM was investigated. All modulation was sinusoidal, and the carrier was a 1 kHz tone. The masking of 16-Hz AM by FM as a function of the modulation frequency of the FM showed the same broad tuning seen with AM modulation masking [Bacon and Grantham, 2575--2580 (1989)]. This is consistent with FM being primarily encoded as AM for small modulation depths. Masking of 16-Hz FM by AM showed broader tuning; this can be attributed to the ``second cue'' for FM hypothesized by Edwards and Viemeister [ 733--740 (1994)]. AM detection thresholds also were obtained as a function of the modulation index, (beta), of the FM masker. Thresholds approached 100% modulation depth for large (beta), indicating an inability to process energy fluctuations that occur in both time and frequency. Finally, thresholds were obtained as a function of the relative phase between the masker and signal modulations. These phase results are discussed with respect to current modulation encoding theories. [Work supported by DC00683.]