Schooneveldt G P, Moore B C
Department of Experimental Psychology, University of Cambridge, England.
J Acoust Soc Am. 1989 Jan;85(1):273-81. doi: 10.1121/1.397734.
These experiments examine how comodulation masking release (CMR) varies with masker bandwidth, modulator bandwidth, and signal duration. In experiment 1, thresholds were measured for a 400-ms, 2000-Hz signal masked by continuous noise varying in bandwidth from 50-3200 Hz in 1-oct steps. In one condition, using random noise maskers, thresholds increased with increasing bandwidth up to 400 Hz and then remained approximately constant. In another set of conditions, the masker was multiplied (amplitude modulated) by a low-pass noise (bandwidth varied from 12.5-400 Hz in 1-oct steps). This produced correlated envelope fluctuations across frequency. Thresholds were generally lower than for random noise maskers with the same bandwidth. For maskers less than one critical band wide, the release from masking was largest (about 5 dB) for maskers with low rates of modulation (12.5-Hz-wide low-pass modulator). It is argued that this release from masking is not a "true" CMR but results from a within-channel cue. For broadband maskers (greater than 400 Hz), the release from masking increased with increasing masker bandwidth and decreasing modulator bandwidth, reaching an asymptote of 12 dB for a masker bandwidth of 800 Hz and a modulator bandwidth of 50 Hz. Most of this release from masking can be attributed to a CMR. In experiment 2, the modulator bandwidth was fixed at 12.5 Hz and the signal duration was varied. For masker bandwidths greater than 400 Hz, the CMR decreased from 12 to 5 dB as the signal duration was decreased from 400 to 25 ms.(ABSTRACT TRUNCATED AT 250 WORDS)
这些实验研究了共调制掩蔽释放（CMR）如何随掩蔽器带宽、调制器带宽和信号持续时间而变化。在实验1中，测量了一个400毫秒、2000赫兹信号的阈值，该信号被带宽从50赫兹到3200赫兹以1倍频程步长变化的连续噪声所掩蔽。在一种条件下，使用随机噪声掩蔽器，阈值随着带宽增加到400赫兹而升高，然后大致保持恒定。在另一组条件下，掩蔽器被一个低通噪声（带宽从12.5赫兹到400赫兹以1倍频程步长变化）相乘（幅度调制）。这在频率上产生了相关的包络波动。阈值通常低于具有相同带宽的随机噪声掩蔽器。对于宽度小于一个临界带宽的掩蔽器，对于具有低调制率（12.5赫兹宽的低通调制器）的掩蔽器，掩蔽释放最大（约5分贝）。有人认为这种掩蔽释放不是“真正的”CMR，而是由通道内线索导致的。对于宽带掩蔽器（大于400赫兹），掩蔽释放随着掩蔽器带宽增加和调制器带宽减小而增加，对于800赫兹的掩蔽器带宽和50赫兹的调制器带宽，达到12分贝的渐近值。这种掩蔽释放的大部分可归因于CMR。在实验2中，调制器带宽固定为12.5赫兹，信号持续时间变化。对于大于400赫兹的掩蔽器带宽，随着信号持续时间从400毫秒减少到25毫秒，CMR从12分贝降至5分贝。（摘要截断于250字）
