John J. Dreher

Effects of Ambient Noise on Speaker Intelligibility for Words and Phrases

The Lombard, or voice reflex, effect results in speech with characteristics different from those of speech that is normally produced. This change of characteristics can be demonstrated as an effective way to combat noise interference during reception. It also demonstrates the advisability of control of the production of speech by the speaker himself, in addition to that offered by equipment, during audiological evaluations.Fifteen naive speakers read words and sentences while noise was being delivered to their headsets. There were five noise conditions. Their speech was recorded, with the noise being kept out of the recording channel, and then limited. Noise was then added to the recording in such a way as to produce a constant speech‐to‐noise ratio. The result was played to 200 American listeners. Results indicate that at a constant speech‐to‐noise ratio of reception speech produced by a talker with masking noise in his cars becomes more intelligible as the masking level rises to a given value. The chang...

Introduction to Acoustical Holography

The principle of reconstructed wavefronts is extended to the formation of visual pictures of acoustical waves. The important relationships used in conventional optical holography that also apply to acoustics are briefly reviewed. It is shown that image formation using the principles of acoustical holography yields better results than do conventional acoustical lens systems, particularly in the presence of turbulence and turbidity. Experiments are described in which coarsely sampled acoustical holograms, made with sound wavelengths of 0.64 in. and longer, have successfully reconstructed images of acceptable quality. The signal‐to‐noise ratio in a sampled acoustical hologram is shown to increase with the number of sampled points as well as with the reduction in the size of the sampling probe. Applications of acoustical holography in different fields are discussed.

Linguistic Considerations of Porpoise Sounds

A brief comparison of intonation and tone languages is given, with criteria of the latter applied to observed whistle contours appearing in underwater recordings of Tursiops truncatus and Langenorhynchus obliquidens.

Effects of Training on Listeners in Intelligibility Studies

Six hundred English monosyllables formed by successive agglutination of initial consonants were presented in high noise to twelve subjects skilled in listening in noise but uninformed as to the words. Alternate training and testing sessions were conducted at weekly intervals following this initial test and differential responses to the words were plotted. Results indicate that corect response in inversely proportional to the number of speech sounds in the monosyllable, with one exception: the two sound monosyllable is superior to all other lengths when subjects have had even one chance to hear words read aloud. Responses grow progressively better, apparently becoming asymptotic to a ceiling value determined by the S/N ratio, at the same time preserving the same order of difference as established by the naive group.PB lists now in current use in audiology are analyzed according to phonetic length and a method for correcting internal inconsistencies lists is proposed.Amount and kind of listener training is ...

Masking of English Words by Prolonged Vowel Sounds

One‐hundred and ten monosyllabic words selected from the Thorndike list of 1000 most frequently occurring words in English to represent equally each of 10 vowels were presented to 300 American listeners in an articulation test. Also tested were 72 spondee words, half selected from those in use in audiological tests and half from those in frequent use in air traffic control, further to represent the same vowel sounds. Masking of the stimuli was accomplished by recording separately each of nine prolonged vowels intoned by a trio of male voices. Results indicate that vowels of equal sound pressure levels differ considerably in masking effectiveness, that words containing specific vowel are not masked optimally by the same vowel, and that spondees are masked by prolonged vowels in the same rank as are the monosyllables. Prolonged vowel sounds with relatively high concentrations of energy between 700 and 1000 cps are most effective as masking agents. Rank order correlation of observed masking effectiveness wit...

Comparison of Hyponasality, Hypernasality, and Normal Voice Quality on the Intelligibility of Two‐Digit Numbers

Six Eastern and General American speakers, using hyponasal, hypernasal, and normal voice qualities recorded random lists of two‐digit numbers for presentation in noise to 11 trained listeners, all of whom had 32 hours practice in listening and testing in noise. Results indicate that, while voice qualities acted in a relatively similar manner at both signal‐to‐noise ratios tested, hypernasality was destructive to intelligibility under both conditions, hyponasality was destructive at the milder noise level, and normal delivery was best throughout.

Phonemic Confusion Vectors

Test responses of listeners from 27 countries who were tested over a period of a year and a half on several versions of word spelling alphabets are examined to determine patterns of intraensemble confusion. On the word level, confusion seems to hinge on the accented vowel, and these confusions are stratified according to the articulatory position of the vowel. Greater discrimination for front vowels than for back is noted, as well as diminishing intraensemble confusion from high‐to‐low‐articulatory position. A method for computing confusion vectors is presented along with a rationale for increasing the phonemic stability of any particular set of words.

Effects of Certain Auditory Environments on Protensity

Normal‐hearing subjects estimated 1‐, 2‐, 4‐, 8‐, 16‐, and 32‐sec time durations under alternating conditions of quiet and four types of high‐level ambient noise. Both duration‐matching and independent estimates were investigated. Errors in quiet were commensurate with the results of previous investigations. Errors attributable to noise were unaffected by frequency of stimulus or response test tones, by varying lapse times following standard‐duration tones in the matching studies, or by two of the four ambient interference noises. A significant monotonic underestimate of time duration was seen to attach to environments of intense, randomly gated, roving tone and to combinations of roving tone and square waves.

Aircraft Cabin Comfort Studies

Several psychophysical tests relating to aircraft cabin comfort studies are described and the results are discussed in relation to speech interference level (SIL) measures. Different conditions of subject motivation and attention are seen to affect the threshold annoyance level, with about 27 sones representing the “normal” operational threshold for both actual and synthetic spectra of propeller‐driven aircraft type.