Some physiological and psychophysical evidence indicates that spectral shape is processed by means of a Fourier‐like analysis of the spectral envelope. A forward masking paradigm in the spectral envelope domain was used to further investigate the properties of such spectral analysis. Detectability of a 50‐ms sinusoidal modulation (ripple) in the amplitude spectrum of a broadband noise was measured when it was preceded by either uniform‐spectrum noise, or by a noise with a same‐frequency ripple (the forward masker). Data showed considerable forward masking of ripple detection when the phase of the masker and that of the signal were the same, but little or no masking when the masker and signal ripples were out of phase. Such results could be explained either by perceptual confusion between the signal and masker or by the adaptation of phase‐sensitive, tuned ripple channels. In a follow‐up study, the masker consisted of a broadband noise with both an on‐frequency and an off‐frequency (nonmasking) ripple. Little or no masking was observed in this study, which is consistent with an explanation based on the perceptual similarity between signal and masker. [Work supported by NIH Grant DC00683.]