Influence of Bandwidth and Reverberation Time upon Preference Evaluation of Speech
Gerhard Martin Sessler, James E. West · The Journal of the Acoustical Society of America · 1967
The subjective influence of bandwidth, center frequency, reverberation time and amplitude and delay of early echoes on speech was studied. Selected sentences spoken by different talkers were recorded in an anechoic chamber by a broad-band system. These sentences were reverberated on a digital computer with reverberation processes corresponding to T60 = 0 to 0.5 sec but having specified early echo structure. After this process, bandpass filtering in half-octave steps with bandwidths of 2–5 oct was applied to the sentences. The test stimuli so generated were presented in paired-comparison tests to a number of subjects. The subjects were asked to select that signal from each pair that they believed to be preferable for communication systems. Evaluation of the subjective results was performed on a digital computer using a factor-analysis program. It was found that of the parameters listed above bandwidth is the single most important one for assessing subjective quality. Also, subjective quality increases in general with decreasing reverberation time. This suggests that, within limits, excessive reverberation can be compensated by an increase in the bandwidth of the transmitted signal.