David B. Hawkins

Description and validation of an LDL procedure designed to select SSPL90.

A new procedure is described for measuring loudness discomfort levels (LDLs) for the purpose of selecting SSPL90 characteristics of hearing aids. The person is seated in sound field wearing a high-output hearing aid (with a known amount of 2 cm3 coupler gain) connected to a personal earmold. The loudness of frequency-specific signals is rated from a series of loudness category descriptors. The LDL is defined in terms of SPL developed in a 2 cm3 coupler, thus making selection of SSPL90 from hearing aid specification sheets practical. Experiments on LDL stability over time and validation of the SSPL90 selection are reported.

A comparison of sound quality judgments for monaural and binaural hearing aid processed stimuli.

Fifteen adults with bilaterally symmetrical mild and/or moderate sensorineural hearing loss completed a paired-comparison task designed to elicit sound quality preference judgments for monaural/binaural hearing aid processed signals. Three stimuli (speech-in-quiet, speech-in-noise, and music) were recorded separately in three listening environments (audiometric test booth, living room, and a music/lecture hall) through hearing aids placed on a Knowles Electronics Manikin for Acoustics Research. Judgments were made on eight separate sound quality dimensions (brightness, clarity, fullness, loudness, nearness, overall impression, smoothness, and spaciousness) for each of the three stimuli in three listening environments. Results revealed a distinct binaural preference for all eight sound quality dimensions independent of listening environment. Binaural preferences were strongest for overall impression, fullness, and spaciousness. Stimulus type effect was significant only for fullness and spaciousness, where binaural preferences were strongest for speech-in-quiet. After binaural preference data were obtained, subjects ranked each sound quality dimension with respect to its importance for binaural listening relative to monaural. Clarity was ranked highest in importance and brightness was ranked least important. The key to demonstration of improved binaural hearing aid sound quality may be the use of a paired-comparison format.

An evaluation of residue features as correlates of voice disorders

Two experiments were conducted to assess the correlations of residue features with some perceptual properties of voice disorders. First, 90 samples of the vowel /a/ produced by patients with various vocal pathologies were analyzed to obtain the residue features, and severity judgments of these vowel samples were obtained. The results of linear multiple regression analysis indicated that the features were highly correlated with the severity ratings. Second, an attempt was made to correlate the residue features with voice qualities. The features were calculated for the vowel /a/ produced by patients with vocal nodules, vocal fold paralysis, and vocal polyps and by normal talkers. Each vowel sample was rated on ten scales of voice quality. The results revealed high correlations among the quality scales so that discrete subject groups could not be formed. Thus, residue features may be useful in assessing the degree of vocal impairment, but their use as correlates of voice quality must await further research.

The effect of signal type on the loudness discomfort level.

Loudness discomfort levels (LDLs) were obtained on 19 normal-hearing subjects with 18 different stimuli using a simple up-down adaptive procedure. The stimuli included five pure tones, five one-third octave bands of noise, five one-third octave bands of filtered multi-talker babble, wideband noise, spondaic words, and sentences. Results indicated there was no significant difference among the three frequency-specific stimuli. However, a significant frequency effect was found. LDLs for the two speech stimuli and wideband noise were not significantly different and were similar to values for signals in the 500 to 4000 Hz region. Although differences among mean LDLs for the various signals were quite small, large intrasubject variability among the signal types and across frequency was observed. This fact would seem to preclude the conclusion that equivalent LDLs would be obtained on an individual regardless of the type of stimulus.

Clinical ear canal probe tube measurements.

This paper describes a variety of areas in which ear canal probe tube microphone measurements can be useful to the audiologist. Areas such as measurement of hearing aid insertion gain to match some predetermined target levels, output sound pressure level in the ear canal (real ear SSPL90), and assessment of FM systems and FM system-hearing aid combinations are discussed. In addition, some variables affecting the accuracy of these measurements and the reliability will be discussed.

Use of probe tube microphone measurements in hearing aid selection for children: some initial clinical experiences.

Some initial experiences are described in which ear canal probe tube microphone measurements are used to determine hearing aid settings for children. Decisions are based upon ideas developed by Seewald and Ross (in Amplification for the Hearing Impaired, New York: Grune & Stratton, 1988: 213-267) and Seewald, Ross, and Stelmachowicz (J Acad Rehab Aud 1987;20:25-37) in which the long term spectrum of speech is amplified to desired sensation levels. Case results from four children are used to demonstrate the application and usefulness of the procedure.

Assessment of FM systems with an ear canal probe tube microphone system.

A technique is described to measure the real-ear performance of an FM system using an ear canal probe tube microphone device. The method involves placement of the FM microphone next to the monitoring (compression) microphone of the probe tube assembly to produce a constant sound pressure level input to the FM system. With the probe tube in the ear canal, a hearing aid alone is measured with a 60 dB SPL input and the FM system attached to the hearing aid (personal FM system) is assessed with an 80 dB SPL input to account for the higher input levels that occur due to the 6 inch distance between the speakers mouth and the FM microphone. This technique permits a rapid comparison of the real-ear response of the hearing aid and the FM system.

Some relations between voice quality judgments and derived acoustic measurements

The use of extracted acoustic features as descriptors of abnormal voice quality was explored by correlating voice quality ratings with the measurements. Sixteen talkers with no history of speech problems and 52 talkers with documented laryngeal pathologies recorded the vowel /ɑ/ using their typical pitch and loudness. Estimates of the excitation for each vowel were obtained using the linear prediction technique of inverse filtering, and the acoustic measurements, known as residue features, were calculated from this waveform. Voice quality estimates were obtained from a panel of judges who rated each vowel on 11 voice quality scales that have been described in the literature. The residue features were used as predictors of average voice quality rating in multiple linear regression analyses. The results are discussed in terms of the voice quality scales that were used most reliably by the judges and the ability of the features to distinguish among various voice quality categories.