Arthur S. House

The Influence of Consonant Environment upon the Secondary Acoustical Characteristics of Vowels

The consonant environments of vowels were varied by forming nonmeaningful stimulus syllables consisting of 72 combinations of six vowels and 12 consonants. The syllables were spoken by subjects, and the duration, fundamental frequency, and relative power of the vowels were measured. All three factors varied significantly in response to changes of the consonant environment. The variations were systematically related to the attributes of the consonants, the most powerful attribute being the presence or absence of vocal fold vibration, followed by manner of articulation and place of articulation, in that order.

Development of a Quantitative Description of Vowel Articulation

A set of parameters that yield a simple yet reasonably accurate description of the articulation of vowel sounds is developed. The articulatory description is potentially useful in a speech band‐width compression system based on the coding of articulatory data. The parameters give information on the position of the tongue constriction, the size of the constriction formed by the tongue, and the dimensions in the vicinity of the mouth opening. An electrical analog of the vocal tract is utilized to obtain experimental relations between the articulatory parameters and the formant frequencies. Contours of vowel articulation are derived from these data. The relation of the contours to classical phonetics is discussed.

On Vowel Duration in English

Average durations of 12 vowels of American English measured in bisyllabic nonsense utterances are reported. The vowels occurred in 14 symmetrical consonantal environments and the utterances were produced by three male talkers. The consonant environments consisted of the voiced and voiceless versions of three stop, one affricate, and three fricative consonant articulations. Four determinants of the characteristic durations of stressed vowels are identified and discussed. The hypothesis is advanced that the primary lengthening of vowels in English—that found in tense vowels and in vowels before voiced constants—is a part of the phonology of the language and is learned by speakers of the language, and that the secondary lengthening of vowels in English—that found in open vowels and in vowels before fricative constants—is a function of the articulatory process itself.

Studies of Formant Transitions Using a Vocal Tract Analog

An electrical analog of the vocal tract is used to obtain experimental relations between certain idealized articulatory parameters and formant frequencies associated with the transitional and stop portions of vowel‐consonant syllables. The data are discussed in terms of the “locus hypothesis” proposed by Delattre, Liberman, and Cooper [J. Acoust. Soc. Am. 21, 769 (1955)] and in terms of simple resonator theory. It is concluded that the results modify the hypothesis that assigns one second‐formant locus to all vowel‐consonant transitions involving a given class of stop consonants. In particular, the second‐formant loci for transitions to velar and bilabial stop consonants appear to vary over a range of frequencies depending on the vowel, while loci for post‐dental stop consonants are relatively invariant. Characteristics of first‐ and third‐formant loci are discussed briefly.

An Experimental Study of Vowel Intensities

One hundred and ten monosyllabic words, 10 for each of the 11 common American vowels, were spoken in isolation by each of 10 subjects. Most of the differences between the mean relative intensities of the vowels were found to be statistically significant. Among the words for a given vowel the intensity of that vowel was found to differ significantly in most instances, variation tentatively attributed to consonantal environment.

Development and Testing of a Formant‐Coding Speech Compression System

The development of a speech‐band‐width compression system employing formant‐coding principles is described. The compression system codes the input speech in terms of seven electrical signals, representing the frequencies of the first three formants, the amplitudes of voicing and of friction, the fundamental vocal frequency, and the frequency of the spectral maximum of the fricative excitation. These signals occupy a total band width of the order of 60 cps and require signal‐to‐noise ratios of approximately 30 db for their transmission.An evaluation of the intelligibility of speech transmitted by the compression system is described. Natural monosyllabic utterances are transmitted through the system and presented to listeners for identification. Vowel and consonant articulation scores are computed and sound confusion matrices are constructed and discussed. The results indicate that correct identification occurred for approximately 80% of the vowels and 25% of the consonants.

Auditory Detection of the Presence and Absence of Signals in Noise

An experiment is described in which detection of the absence of signal remained high and relatively constant while detection of intermixed signals varied over the threshold region as a function of signal voltage. Statistical signal detection thresholds of observers with set to detect absence of signal were approximately 2 db lower than those of observers with set to detect signal.

Auditory Testing of a Formant‐Coding Speech Compression System

An evaluation of the intelligibility of speech transmitted by a formant‐coding compression system is described. The compression system codes the input speech in terms of six electrical signals, representing the frequencies of the first three formants, the intensity of voicing and of friction, and the fundamental vocal frequency. These signals occupy a total band width of approximately 50 cps and require signal‐to‐noise ratios of approximately 30 db for their transmission. Natural monosyllabic utterances are transmitted through the compression system and are presented to listeners for identification. Vowel and consonant articulation scores are computed and sound‐confusion matrices are constructed. The contribution to intelligibility of various components of the system and the inherent limitations of the system are examined and discussed. [This work was supported in part by the Air Force Cambridge Research Center under Contract No. AF 19(604)‐626.]