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Biomedical subjects

A M Engebretson

Publications and source records attributed to A M Engebretson.

9 recordsLinked to original sources
PubMed1992

Behavioral assessment of CID's benchtop (version 2) digital hearing aid: noise reduction.

Perceptual rating and word identification procedures were used to evaluate the efficacy of several digital hearing aid adaptive and nonadaptive noise reduction algorithm parameters. The study included 15 hearing-impaired adults listening to speech at soft, moderate, and loud input levels in quiet, fan noise, and multitalker babble noise. The results suggest that hearing-impaired listeners can make clarity judgments that result in the selection of algorithms that optimize word intelligibility at soft and moderate speech levels. The spectral adaptation requirements, however, were not constant with signal level.

Adaptation, Physiological↗
PubMed1987

Development of an ear-level digital hearing aid and computer-assisted fitting procedure: an interim report.

Recent progress on the development of an ear-level digital hearing aid is described. The work includes development of a body-wearable digital hearing aid and a computer-based hearing evaluation system that exploits the flexibility afforded by digital signal processing. The prescriptive criteria and fitting procedure used with the digital hearing aid are described briefly. Design considerations in the development of VLSI chips for an ear-level unit are discussed.

Audiometry↗
PubMed1983

The accuracy of formant frequency measurements: a comparison of spectrographic analysis and linear prediction.

The accuracy of spectrographic techniques and of linear prediction analysis in measuring formant frequencies is compared. The first three formant frequencies of 90 synthetic speech tokens were measured by three experienced spectrographic readers and by linear prediction analysis. For fundamental frequencies between 100 and 300 Hz, both methods are accurate to within approximately +/- 60 Hz for both first and second formants. The third formant can be measured with the same degree of accuracy by linear prediction, but only to within +/- 110 Hz by spectrographic means. The accuracy of both methods decreases greatly when fundamental frequency is 350 Hz or greater. These limits of measurement appear to be within the range of the difference limens for formant frequencies.

Communication Devices for People with Disabilities↗
PubMed1982

A computer program for fitting a master hearing aid to the residual hearing characteristics of individual patients.

The electroacoustic characteristics of an experimental master hearing aid are determined by the choice of transducers and settings of 26 controls which include a preamplifier, the gains and limiting levels in each of 12 channels as well as the gain of a final power amplifier. Here, a computer program which aids in the fitting of the electroacoustic characteristics of this aid to the characteristics of a patient's residual hearing is described. The patient's audiologic data and the hearing-aid parameters are entered into the computer and the gain and limiting level of each channel of the hearing aid are adjusted until an appropriate fit is achieved. The results of the fitting procedure are displayed on a graphics terminal. Permanent copies of the results can be produced on a printer-plotter. Included in the results for each of 12 channels are (1) the discomfort level, most comfortable listening level, and hearing threshold of the patient, and (2) the maximum output and noise floor of the hearing aid as well as the aided speech level. This approach has simplified the problem of fitting a complicated hearing aid to a patient's residual hearing and seems to offer attractive possibilities for fitting commercial hearing aids in the future.

Acoustics↗
PubMed1979

Some effects of deafness on the generation of voice.

Glottal volume-velocity waveform data were collected from twenty male and female hearing-impaired adolescents by means of a reflectionless tube. The subjects each provided samples of phonation in normal- and soft-voice modes and in a three-syllable word with primary stress on the medial syllable. Analysis of the data, in comparison with characteristics of phonation produced by normally hearing subjects, indicates that deafness affects primarily the time-varying characteristics of the glottal source. Among the hearing-impaired subjects, the following abnormalities were noted; diplophonia and creaky-voice episodes at the onset or middle of phonation, and irregular patterns of change in the frequency and intensity of the glottal waveform. For some subjects, the period-to-period changes of frequency and intensity may be greater than normal. For the hearing-impaired subjects, the shape of the isolated glottal pulse and its spectrum are similar or identical to normal, while striking abnormalities may be seen in the way the glottal pulse changes over time. The effect of deafness is thus that it may prevent a speaker from learning the phonatory consequences of the muscular gestures which maintain and alter vocal-fold tension and subglottal air pressure dynamically in the production of voice.

Adolescent↗
PubMed1978

Indirect assessment of the contribution of subglottal air pressure and vocal-fold tension to changes of fundamental frequency in English.

The contributions of vocal-fold tension and of subglottal air pressure to changing fundamental frequency F0 are indirectly assessed by comparing human glottal-source data with synthetic glottal waveforms generated by the Ishizaka-Flanagan two-mass model of vocal-fold vibration. In this model, synthetic male and female glottal waves may be generated with known values of subglottal air pressure and vocal-fold tension. Human glottal waves were recorded with a reflectionless tube into which ten male and female adults phonated. The subjects produced interrogative (rising F0) and declarative (falling F0) glides and trisyllabic words with primary stress on the initial, medial, or final syllable. Two types of change in the glottal wave over time are possible, depending on whether F0 is changed primarily by vocal-fold tension or by subglottal air pressure. Comparison of the natural and synthetic glottal waves indicates that (1) the rise of frequency in interrogative words is due principally to increasing vocal-fold tension, while (2) the fall of frequency in declarative words is due principally to decreasing subglottal air pressure; (3) in the polysyllabic words, the change of frequency within syllables resembles that of the declarative monosyllables and appears due primarily to changes of subglottal air pressure; and (4) the heightened f0 of the stressed syllable is due to an increase in the vocal-fold tension, typically accompanied by increased subglottal air pressure.

Acoustics↗
PubMed1977

Study of variations in the male and female glottal wave.

A reflectionless metal tube which can act as a pseudoinfinite termination of the vocal tract was used to collect glottal volume-velocity waveforms produced by 10 male and female adult subjects. From each subject glottal volume-velocity samples were collected of normal, loud, and soft voice; falsetto and creaky voice; monosyllables with rising and failing intonation; and three-syllable utterances containing primary lexical stress on one of the three syllables. Analysis of the data indicates a wide variation of the glottal waveform shape, its rms intensity and fundamental frequency, phase spectrum, and intensity spectrum. It is observed that as the fundamental frequency changes over time, the glottal source varies in one of two different ways. In one type of change, the harmonic relations in the glottal spectrum become steeper as fundamental frequency rises. In a different type of glottal-wave change, relations between harmonics tend to remain the same despite a change in the fundamental frequency; the source spectrum in this case is simply shifted along the frequency and amplitude axes as a function of fundamental frequency. To account for these variations in the glottal source, at least three factors must be known: the sex of the speaker, the voice register in which he phonates, and the linguistic context in which the phonation occurs.

Acoustics↗