PEAK-CLIPPING

Increasing the intelligibility of transmitted speech by “clipping,” or eliminating, high intensity sounds and amplifying the low intensities.Peak-clipping is accomplished by special circuits in radio transmitters, walkie-talkies, public address systems, and hearing aids. It is based on experiments of physiological psychologists and acoustical specialists who have shown that the high intensity (loud) components of speech contribute little to intelligibility. The reason is that these components are usually (in English, at least) the low frequency (low-pitched)sounds, mainly vowels, and these are not so essential to understanding as the high frequency sounds, which are primarily consonants. The technique therefore cuts out the lower tones and amplifies the higher tones of speech. This enables the hearing aid or other system to utilize its power to the best advantage. It also helps to eliminate noise in the system since noise is primarily high intensity, low frequency sound.Peak-clipped speech sounds rough and distorted, but its comprehensibility is increased. If the reverse is done, by a process called center-clipping, in which the low intensity, high frequency tones are eliminated, speech becomes totally incomprehensible. Both processes are known as “amplitude distortions,” and are important for both their practical applications and their theoretical implications in the study of speech perception.