Difference Limens for Complex Frequencies

Abstract

Most of the stimuli that are commonly experienced by the ear, especially in the perception of speech, are transient sounds of a more complex nature than the pure tones and clicks usually studied in psychoacoustics. A natural building block for such complex sounds is the damped sinusoid of the form e−σt cosωt, since this is a basic component of the response obtained when any linear system with resonances undergoes transient excitation. As an introduction to a study of the perception of waves with such “complex” frequencies, difference limens in frequency have been measured for single stimuli of this form, over a range of values of the parameters σ and ω. For small values of the damping σ the DL is close to the value for pure tones, but as the damping increases, discriminability deteriorates rapidly. In the range of σ between 150 and 500 sec−1 (bandwidth between 50 and 160 cps), the variation of DL with frequency exhibits a minimum between 500 and 1000 cps. A similar investigation of the same DL's has been made for series of these stimuli repeated at a frequency comparable with the fundamental pitch in vowel sounds. The results of these experiments are used to estimate the degree of precision that is possible in the perception of the formants that characterize speech sounds.