A multichannel model is discussed which describes effects of spectral and temporal integration in amplitude-modulation detection and masking. Envelope fluctuations within each auditory channel are analyzed with a modulation filterbank. The parameters of the filterbank are the same for all auditory filters and were adjusted to allow the model to account for modulation detection and modulation masking data with narrow-band carriers at a high center frequency. In the detection stage, the outputs of all modulation filters from all excited peripheral channels are combined linearly with optimal weights. To integrate information across time, a ``multiple-look'' strategy is implemented within the detection stage. Model predictions are compared with literature data from Houtgast [J. Acoust. Soc. Am. 85, 1676--1680 (1989)]. The following three conditions were reproduced with a deviation of less than 3 dB between experiment and simulation. (1) Masking of test modulations in the range 2 to 64 Hz by a narrow-band masker modulation at 4, 8, or 16 Hz. (2) Modulation masking as a function of the masker-modulation level. (3) Modulation masking as a function of the masker-modulation bandwidth. The results from the simulations further support the hypothesis that amplitude fluctuations are processed by modulation-frequency-selective channels.