Optimization of a Prefiltering Technique for the Production of Speech Highly Immune to Noise
Russell J. Niederjohn, Ian B. Thomas · The Journal of the Acoustical Society of America · 1969
Modification of speech by high-pass filtering and infinite amplitude clipping produces a signal having substantially greater intelligibility than that of normal speech over a wide range of signal-to-noise ratios. The cutoff frequency and attenuation slope of the high-pass filter have been varied to determine the values of these parameters which yield the highest intelligibility. The results of extensive intelligibility tests show that suppression of the first formant prior to clipping is the essential factor contributing to the higher intelligibility of modified speech. At equal signal and noise levels of 90 dB intelligibility scores greater than twice those for normal speech are consistently obtained at a number of filter settings. [Work supported by the National Aeronautics and Space Administration.]