An investigation of several frequency-domain processing methods for enhancing the intelligibility of speech in wideband random noise

This paper describes results of a study of several frequency-domain processing methods for enhancing the intelligibility of speech in wideband random noise. Five categories of processing methods are explored. These include the INTEL technique, a technique based upon minimum mean square filtering, several techniques based upon subtraction of the estimated spectrum of the noise from the spectrum of the speech plus noise, spectrum squaring, and techniques based upon pitch frequency analysis. The results of this study have provided considerable insight into the individual processing methods and into the use of frequency-domain processing methods in general. A major conclusion of this work is that all successful techniques investigated are similar in that they are an attempt to emphasize spectral components as a function of the amount by which they exceed the noise. A second conclusion is that unless the spectral weighting within a time-window is relatively smooth, it will introduce conspicuous background distortion.