In an effort to evaluate the importance of across-frequency comparisons of envelope patterns in comodulation masking release (CMR) experiments and to compare joint effects of target–masker frequency separation for both CMR and modulation detection interference (MDI) tasks, thresholds were measured for three tasks. These tasks were: (a) the detection of sinusoidal amplitude modulation (SAM) of a tone, (b) the detection of a reduction in the modulation depth of a fully modulated SAM tone, and (c) the detection of a tone added to a narrow band of noise. Thresholds were obtained for the target alone and for the target presented with two maskers. For the detection of SAM, thresholds did not depend on whether the modulation patterns of the target and masker elements were the same or random. For the latter two tasks, modulator phase effects were apparent for target–masker frequency separations less than 1–2 oct. In contrast, past work has shown that observers can compare modulator envelope phases across frequency separations larger than 1–2 oct [Strickland et al., J. Acoust. Soc. Am.86, 2160–2166 (1989); Yost and Sheft, J. Acoust. Soc. Am.85, 848–857 (1989)]. In a second experiment, thresholds for the detection of SAM were obtained after prolonged exposure to a fully modulated SAM tone. For four of the five observers, modulation-rate specific adaptation was obtained for test/adapting carrier-frequency separations approaching 2 oct below and 1 oct above the adaptor.