Strickland E A, Dhar S
Department of Audiology and Speech Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
J Acoust Soc Am. 2000 Aug;108(2):735-42. doi: 10.1121/1.429606.
Experiments were performed to determine under what conditions quasi-frequency-modulated (QFM) noise and random-sideband noise are suitable comparisons for AM noise in measuring a temporal modulation transfer function (TMTF). Thresholds were measured for discrimination of QFM from random-sideband noise and AM from QFM noise as a function of sideband separation. In the first experiment, the upper spectral edge of the noise stimuli was at 2400 Hz and the bandwidth was 1600 Hz. For sideband separations up to 256 Hz, at threshold sideband levels for discriminating AM from QFM noise, QFM was indiscriminable from random-sideband noise. For the largest sideband separation used (512 Hz), listeners may have used within-stimulus envelope correlation in the QFM noise to discriminate it from the random-sideband noise. Results when stimulus bandwidth was varied suggest that listeners were able to use this cue when the carrier was wider than a critical band, and the sideband separation approached the carrier bandwidth. Within-stimulus envelope correlation was also present in AM noise, and thus QFM noise was a suitable comparison because it made this cue unusable and forced listeners to use across-stimulus envelope differences. When the carrier bandwidth was less than a critical band or was wideband, QFM noise and random-sideband noise were equally suitable comparisons for AM noise. When discrimination thresholds for QFM and random-sideband noise were converted to modulation depth and modulation frequency, they were nearly identical to those for discrimination of AM from QFM noise, suggesting that listeners were using amplitude modulation cues in both cases.
进行了实验，以确定在何种条件下准频率调制（QFM）噪声和随机边带噪声适合在测量时间调制传递函数（TMTF）时与调幅（AM）噪声进行比较。测量了将QFM与随机边带噪声区分开以及将AM与QFM噪声区分开的阈值，作为边带间隔的函数。在第一个实验中，噪声刺激的最高频谱边缘为2400 Hz，带宽为1600 Hz。对于高达256 Hz的边带间隔，在区分AM与QFM噪声的阈值边带水平下，QFM与随机边带噪声无法区分。对于所使用的最大边带间隔（512 Hz），听众可能利用了QFM噪声中的刺激内包络相关性来将其与随机边带噪声区分开。当刺激带宽变化时的结果表明，当载波宽于临界带宽且边带间隔接近载波带宽时，听众能够利用此线索。刺激内包络相关性在AM噪声中也存在，因此QFM噪声是合适的比较对象，因为它使该线索无法使用，并迫使听众利用刺激间包络差异。当载波带宽小于临界带宽或为宽带时，QFM噪声和随机边带噪声同样适合与AM噪声进行比较。当将QFM和随机边带噪声的辨别阈值转换为调制深度和调制频率时，它们与区分AM与QFM噪声的阈值几乎相同，这表明听众在两种情况下都使用了调幅线索。
