Monaural and binaural subjective modulation transfer functions in simple reverberation
Abstract
The temporal intensity envelope of a signal is filtered by the transmission channel through which it passes. The amount of reduction for a given envelope, or modulation, frequency has been called the modulation transfer function (MTF) and can be derived from the impulse response of the transmission channel [Schroeder, M.R. (1981) Modulation transfer-functions: De nition and measurement, Acustica, 49, 179-182]. The envelope of a speech signal is critical for intelligibility, and the speech transmission index (STI) predicts the intelligibility of speech through a given transmission channel based on its MTF [Houtgast, T. and Steeneken, H.J.M. (1973) Modulation transfer-function in room acoustics as a predictor of speech intelligibility, Acustica, 28, 66-73]. In the present study, the results of intensity modulation detection experiments with broadband noise carriers are reported in monaural and binaural conditions, with single reflections at different arrival times in the two ears and with a simulated room impulse response. The monaural data describe a subjective MTF, which is similar to the physical MTF. Binaurally, the thresholds are consistently lower than the monaural thresholds, especially at frequencies where there is a large interaural modulation phase difference. These data show that binaural detection thresholds can be better than either ear alone and better than the predictions from either ear’s physical MTF.
References
Christiansen, T. U., and Greenberg, S. (2005). “Frequency selective filtering of the modulation spectrum and its effect on consonant identification,” 21st Danavox Symposium, Hearing Aid Fitting, edited by A. N. Rasmussen, and T. Poulsen.
Houtgast, T., and Steeneken, H. J. M. (1973). “The modulation transfer function in room acoustics as a predictor of speech intelligibility,” Acustica 28, 66–73.
Houtgast, T., and Steeneken, H. J. M. (1985). “A review of the MTF concept in room acoustics and its use for estimating speech intelligibility in auditoria,” J. Acoust. Soc. Am. 77, 1069–1077.
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Schroeder, M. R. (1981). “Modulation transfer-functions: Definition and measurement,” Acustica 49, 179–182.
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