Intelligibility of speech processed by a spectral contrast enhancement procedure and a binaural procedure

The study reported was undertaken as an attempt to improve
the intelligibility of selected speech signals (numerical test) masked by a
speech-shaped noise, by a proposed algorithm of the speech signal processing
based on the spectral contrast enhancement and binaural procedure. The spectral
contrast enhancement involved the transformation of the speech signal spectrum
to achieve an increase in the level of the amplitude between subsequent minima
and maxima of individual formants. The binaural procedure involved the
determination of the interaural time difference (ITD) and the interaural
intensity difference (IID) in order to select and enhance the fragments reaching
the listener from the front. The intelligibility of speech processed by the
algorithm was compared to that of the unprocessed speech for different spatial
separations between the signal and the noise sources and for a few signal to
noise ratios. The results have shown that the intelligibility of the speech
presented against the noise significantly depends on the angle between the
directions of the signal and the noise. The intelligibility of speech is much
larger when the noise and the speech reach the observer from different
directions, i.e. when their sources are spatially separated. In general, the
algorithm improves the intelligibility of numerical tests presented at the
background of the noise by a few percent and the greatest improvement has been
observed for low signal to noise ratios. The algorithm performance was different
for each hearing impaired subject with binaural hearing loss. To get an
objective assessment of the algorithm performance it should be optimised and
tested on a larger group of subjects for more diverse sound material.