<p>A rippled-spectrum sound signal has an envelope periodicity which is not present in a continuous-spectrum signal. The studies reported here investigated the role of the signal envelope in the task of discriminating signals with rippled spectra. The test signal consisted of rippled-spectrum noise with a spectral band of 2 oct. The reference signal consisted of continuous-spectrum noise. Listeners with different hearing sensitivity took part in the experiments. The ripple phase reversal test was used to assess the discrimination of the densities of spectral patterns. Density discrimination thresholds were determined in relation to the width of rippled spectra for two types of signals: without additional envelope modulation and with additional envelope modulation. Decreases in hearing sensitivity led to decreases in spectrum density discrimination for all values of spectral ripple width. Adding amplitude modulation led to deterioration of discrimination for all listeners for all spectral rippled widths, though not to the thresholds determined by the spectral mechanism. It is suggested that discrimination of the rippled spectral structure in this task is determined by the latent temporal structure of the rippled spectrum sound signal rather than by the periodicity of the envelope. Addition of modulation reduces the perception of repetition pitch.</p>