Speech enhancement for the hearing impaired by envelope filtering on a loudness scale

Abstract

Dynamic compression systems for sensorineural hearing‐impaired subjects reduce intensity fluctuations, although they are an important cue for understanding speech. To overcome this effect, an envelope high‐pass filter operating in the loudness domain is evaluated, which even enhances these intensity modulations: The output of a filterbank is low‐pass filtered to extract the envelope of incoming speech. Loudness scaling data from normal listeners and from each individual impaired listener is used to convert the envelope to a loudness scale value and to convert the high‐pass‐filtered loudness back to the “desired” envelope value, respectively. The output signal is finally obtained by summing up the filterbank channels after correcting their amplitude. Loudness scaling and intensity modulation discrimination data of several sensorineural hearing‐impaired subjects will be presented, as well as speech intelligibility scores for a German CVC rhyme test with and without the algorithm. First results indicate that even no loudness filtering improves speech intelligibility in a wide range of input levels. However, the effect of high‐pass filtering in the loudness domain is only moderate. [Work supported by Deutsche Forschungsgemeinschaft.]