Treurniet W C, Boucher D R
Communications Research Centre, Ottawa, Ontario, Canada.
J Acoust Soc Am. 2001 Jan;109(1):306-20. doi: 10.1121/1.1328791.
The role of harmonicity in masking was studied by comparing the effect of harmonic and inharmonic maskers on the masked thresholds of noise probes using a three-alternative, forced-choice method. Harmonic maskers were created by selecting sets of partials from a harmonic series with an 88-Hz fundamental and 45 consecutive partials. Inharmonic maskers differed in that the partial frequencies were perturbed to nearby values that were not integer multiples of the fundamental frequency. Average simultaneous-masked thresholds were as much as 10 dB lower with the harmonic masker than with the inharmonic masker, and this difference was unaffected by masker level. It was reduced or eliminated when the harmonic partials were separated by more than 176 Hz, suggesting that the effect is related to the extent to which the harmonics are resolved by auditory filters. The threshold difference was not observed in a forward-masking experiment. Finally, an across-channel mechanism was implicated when the threshold difference was found between a harmonic masker flanked by harmonic bands and a harmonic masker flanked by inharmonic bands. A model developed to explain the observed difference recognizes that an auditory filter output envelope is modulated when the filter passes two or more sinusoids, and that the modulation rate depends on the differences among the input frequencies. For a harmonic masker, the frequency differences of adjacent partials are identical, and all auditory filters have the same dominant modulation rate. For an inharmonic masker, however, the frequency differences are not constant and the envelope modulation rate varies across filters. The model proposes that a lower variability facilitates detection of a probe-induced change in the variability, thus accounting for the masked threshold difference. The model was supported by significantly improved predictions of observed thresholds when the predictor variables included envelope modulation rate variance measured using simulated auditory filters.
通过使用三选一的强制选择法，比较谐波掩蔽器和非谐波掩蔽器对噪声探针掩蔽阈值的影响，研究了谐波性在掩蔽中的作用。谐波掩蔽器是通过从具有88赫兹基频和45个连续泛音的谐波序列中选择泛音集来创建的。非谐波掩蔽器的不同之处在于，泛音频率被扰动到附近的值，这些值不是基频的整数倍。谐波掩蔽器的平均同时掩蔽阈值比非谐波掩蔽器低多达10分贝，并且这种差异不受掩蔽器电平的影响。当谐波泛音之间的间隔超过176赫兹时，这种差异会减小或消除，这表明该效应与听觉滤波器对谐波的分辨程度有关。在前向掩蔽实验中未观察到阈值差异。最后，当在由谐波带侧翼的谐波掩蔽器和由非谐波带侧翼的谐波掩蔽器之间发现阈值差异时，涉及到一种跨通道机制。为解释观察到的差异而开发的一个模型认识到，当滤波器通过两个或更多正弦波时，听觉滤波器输出包络会被调制，并且调制率取决于输入频率之间的差异。对于谐波掩蔽器，相邻泛音的频率差是相同的，并且所有听觉滤波器具有相同的主导调制率。然而，对于非谐波掩蔽器，频率差不是恒定的，并且包络调制率在不同滤波器之间变化。该模型提出，较低的变异性有助于检测探针引起的变异性变化，从而解释了掩蔽阈值差异。当预测变量包括使用模拟听觉滤波器测量的包络调制率方差时，该模型得到了对观察到的阈值的显著改进预测的支持。
