Difference Limen for Formant Frequencies Obtained by Method of Adjustment Procedure

Abstract

Difference limens (DLs) formant frequencies of steady-state signals resembling vowels have been investigated using method-of-adjustment procedure with a computer-controlled terminal-analog synthesizer. The DLs were obtained in a standard manner as a function of types of source (pulse or noise), of fundamental frequencies in the case of pulsed source, of duration, and as a function of the number and location of the formants. Values obtained under noise and pulse source conditions were about equal and smaller than those reported by Flanagan [J. Acoust. Sec. Amer. 27, 613–617 (1955)]. This difference is probably due to different procedures and signal patterns. Fundamental frequency did affect DL values significantly in the range used. In the test signals in which higher formants had smaller amplitudes, DL values tended to become larger for the higher formants. This tendency was diminished, however, in the experiments in which amplitudes of lower formants were reduced, suggesting the presence of masking by lower formants. Applications of the method-of-adjustment procedure using terminal-analog synthesizers to problems of hearing pathology are discussed.