Spectra of Fricative Noise in Human Speech

This paper describes the results of a spectrographic analysis of a number of voiceless fricatives. The sounds are shown to be capable of description in terms of the frequencies of the lower and upper limits of energy present, the presence or absence of formant-like concentrations of energy, and the over-all relative intensity of the sounds. The sounds investigated fall into three groups: front, mid and back, corresponding to the regions of the vocal tract within which they are produced. Sounds in the front group have a long spectrum, with little patterning of peaks of energy; their relative intensity is low. Sounds in the mid group have a short spectrum, with the main region of energy at a higher frequency than in the other groups; their relative intensity is high. Sounds in the back group have a spectrum of medium length, exhibiting a formant-like patterning of energy; their relative intensity is intermediate between the other groups. Tentative criteria are advanced for distinguishing between members of each group. Combining this evidence with general phonetic knowledge it is possible to make a number of statements about other categories of sounds which include a component of fricative noise: i.e. voiced fricatives, stops, and affricates.