Acoustic Loci and Transitional Cues for Consonants

Abstract

Previous studies with synthetic speech have shown that second-formant transitions are cues for the perception of the stop and nasal consonants. The results of those experiments can be simplified if it is assumed that each consonant has a characteristic and fixed frequency position, or locus, for the second formant, corresponding to the relatively fixed place of production of the consonant. On that basis, the transitions may be regarded as "movements" from the locus to the steady state of the vowel.The experiments reported in this paper provide additional evidence concerning the existence and positions of these second-formant loci for the voiced stops, b, d, and g. There appears to be a locus for d at 1800 cps and for b at 720 cps. A locus for g can be demonstrated only when the adjoining vowel has its second formant above about 1200 cps; below that level no g locus was found.The results of these experiments indicate that, for the voiced stops, the transition cannot begin at the locus and go from there to the steady-state level of the vowel. Rather, if we are to hear the appropriate consonant, the first part of the transition must be silent. The voiced stops are best synthesized by making the duration of the silent interval equal to the duration of the transition itself.An experiment on the first formant revealed that its locus is the same for b, d, and g.N an earlier experiment •.•' we undertook to find out whether the transitions (frequency shifts) of the second formant--often seen in spectrograms in the region where consonant and vowel join--can be cues for the identification of the voiced stop consonants. For that purpose we prepared a series of simplified, handpainted spectrograms of transition-plus-vowel, then converted these patterns into sound and played the recordings to naive listeners for judgment as b, d, or g. The agreement among the listeners was, in general, sufficient to show that transitions of the second formant can serve as cues for the identification of the stops and, also, to enable us to select, for each vowel, the particular transitions that best produced each of the stop consonant phones. These transitions are shown in Fig. 1.We found in further experiments 2 that these same second-formant transitions can serve as cues for the unvoiced stops (p-t-k) and the nasal consonants (m-n-•), provided, of course, that the synthetic patterns are otherwise changed to contain appropriate acoustic cues for the voiceless and nasal manners of production. Moreover, and more important for the purposes of this paper, the results of these experiments plainly indicated a relationship between second-formant transition and articulatory place of production. Thus, the same second-formant transitions that had been found to produce b proved to be appropriate also for the synthesis of p and m, which, like b, are articulated at the lips; the second-formant transitions that produced d produced the consonants t and n, which have in • Liberman, Delattre, Cooper, and Gerstman, Psychol. Monogr. 68, No. 8, 1-13 (1954). forma...

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