Articulation Reduction by Combined Distortions of Speech Waves

Abstract

Previous investigators have shown that speech waves can undergo any one of a number of severe forms of distortion in low ambient noise levels without serious reduction of word articulation. There are well-known notable exceptions (e.g., center clipping). However, it is not enough to avoid these exceptional forms of distortion. In the study reported here it has been demonstrated that combinations of speech-wave distortions, which individually are quite innocuous with regard to word articulation, can be devastating in their combined effect, even in the absence of serious noise. Four types of speech-wave distortion were studied, individually and in combination, as follows: gross attenuation of high-frequency components, multiple echo, random amplitude modulation, and gross irregularity of response-frequency characteristic. Ambient noise was also a controlled environmental condition in some phases of the investigation. * This work was sponsored by the U.S. Air Force under Contract AF33(616)-2320. Paper delivered at 50th meeting of the Acoustical Society of America, December 16, 1955, at Providence, Rhode Island. • J.P. Egan et al., "The performance of communication equipment in noise," Harvard University Psycho-Acoustic Laboratory Report OSRD 901 (MHR-21) (1942).

Signal processing to improve speech intelligibility in perceptive deafness

“…Speech can suffer progressive, severe at-IMPROVING SPEECH PERCEPTION FOR THE DEAF tenuation above 500 Hz without serious effect on its intelligibility for normals, as reported by Martin, Murphy, and Meyer (1956), but post-compression frequency equalization may nevertheless be important to the signal processing. Figure 2 shows that without treble•boost a significant portion of the compressed signal would remain below the subject's hearing threshold, assuming that lower-frequency elements were kept at comfortable levels, and it should be noted that above 2 kHz a 10-dB change of level for this subject is approximately equivalent, in its effect on loudness, to a 30-dB change for normals.…”