Effects of Various Types of Nonlinear Distortion upon the Intelligibility of Speech
J. C. R. Licklider, Richard Held · The Journal of the Acoustical Society of America · 1952
Articulation tests were conducted under uniform conditions (same talkers, same listeners, randomized block design of experiment) to compare the effects upon intelligibility of various types and amounts of nonlinear distortion. The types included peak clipping (both symmetrical and asymmetrical), center clipping, linear rectification, and parabolic (“square-law”) rectification. The results confirm previous reports that intelligibility is highly resistant to symmetrical peak clipping (80 percent word articulation with infinite peak clipping). They show that asymmetrical peak clipping is almost entirely without detrimental effect upon intelligibility until more than half the speech wave is eliminated (98 percent word articulation with half-wave rectification). In addition, the results provide a basis for comparing effects of odd and even harmonic distortion, for comparing the effects of noise that enters the system at a point ahead of the nonlinear circuit with effects of noise that enters at a point following the nonlinear circuit, and for deciding what are tolerable limits for nonlinear distortion in speech communication systems.