Effects of Multiple, Narrow Pass Band Filtering on the Intelligibility of Speech

Abstract

It was reported [J. Acoust. Soc. Am. 29, 1262 (A) (1957)] that speech passed through several half-octave band pass filters spaced at intervals along the speech spectrum was more intelligible than one would predict on the basis of the Articulation Index. The present study is a further exploration of communication over this type of a multiple, pass band system. PB word and sentence intelligibility tests were conducted with unfiltered speech and with speech filtered (1) by a 1600-cps low pass filter, (2) by a 500–2000-cps band pass filter, (3) by a 1000–2500-cps band pass filter, and (4) by various configurations of one, two, or three band-pass filters, each 500 cps wide. The positions of the center frequencies of the 500-cps band pass filters were systematically varied during the tests. If we use constant speech intelligibility as our criterion, the results indicate that the total “effective” band width required for the multiple pass band system is less than that required for the best contiguous pass band systems by a factor of 2 or 3. Also, a feature of the signal resulting from this multiple sampling in the frequency domain is that it sounds “natural” and the identity of a talker's voice appears to be maintained. (This study was performed under Contract No. Da-36-039 SC-78078 with the U. S. Army Signal Research and Development Laboratory, Fort Monmouth, New Jersey.)