A new theory for multitone masking.

In order to explain masked thresholds of a tonal probe centered between two tone maskers, Green [J. Acoust. Soc. Am. 37, 802-813 (1965)] introduced his famous energy-detection model. We argue that the model is in some respects inadequate and inconsistent with measurements of roughness, at least one psychological correlate of temporal fluctuations. Furthermore, it requires the assumption that tones interact over frequency distances considerably beyond a critical bandwidth. Therefore we propose an alternative theory that allows reconciliation of Green's measurements with the commonly accepted critical-band hypothesis. Our model is based on the hypothesis that the auditory system is capable of performing a spectral analysis of the time pattern of the waveform envelope. Important effects of probe type (noise, tone, or complex) and phase between masker and probe seem easily explained by the model. Also, the differences between two- and four-tone masking are successfully predicted. Finally, as a byproduct, our theory offers and explanation for the just noticeable amplitude modulation (AM) and frequency modulation (FM) of a sinusoidal carrier.