Synthesis By Rule as a Tool for Phonological Research
The phonologist, having analysed a corpus of phonetic data and proposed tentative phonological rules, must test these rules by generating novel utterances for acceptance or rejection by an informant. There are certain methodological problems in such testing which could be avoided by the use of speech synthesized by rule. Synthesis by rule is now a practical technique, and a synthesis-by-rule system at Haskins Laboratories has been used to formulate rules for General American English.
Performance of a Speech Synthesis System
A system for synthesizing speech from a phonetic input is described. A string of phonetic symbols representing the sentence to be uttered is transformed into the control signals required by a parametric speech synthesizer using a small digital computer. The performance of the system was investigated by listening tests. In the first set of experiments consonant-vowel syllables were synthesized, and presented to listeners for identification. The vowels were readily identified, but the fricatives less so. In the second set of experiments the intelligibility of synthesized sentences was examined. It was found that after about an hour of transcribing the sentences, listeners identified about 90% of the words correctly.
Perceptual Study of English /l/ Allophones
Once the broad set of perceptual cues distinguishing utterances is isolated, speech synthesis can be further used to answer detailed questions about the process of perception. Such questions are basic to application of knowledge about speech to synthesis‐by‐rule. Improvement of synthesis rules may result from adjusting the rules to maximize quality of long utterances, but more restricted, detailed perceptual investigations are also necessary. The /l/ phoneme fits into no convincing matrix of feature oppositions and is difficult to synthesize; so five questions were examined for six /l/ allophones—initial and final in the contexts /i,a,u/. (1) How do the optimal patterns vary as a function of context? (2) What is the importance of spectral discontinuities? (3) Do the /l/ steady state and transition have interdependent perceptual effects? (4) Is the same priority of cues shown in quality judgments at high intelligibility levels and in effects on recognition of an ambiguous stimulus? (5) What modification do...