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Journal of the Acoustical Society of America

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Jun 1977

Volume 61, Issue S1, pp. S1-S96

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back to top Session A. Musical Acoustics I: Electronic Music
Invited Papers
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New approaches to analog music synthesis (A)

B. A. Hutchins

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S1-S1 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Analog, voltage‐controlled electronic music synthesizers have been developed over a period of about ten years into a fairly standard commercial product. While these synthesizers are unquestionably useful for certain types of music, they are also limited in many ways. A number of fairly simple “new modules” involving conventional circuitry and conventional electronic components can be developed and added to the conventional set of synthesizer modules. New types of excitation sources for driving processing type modules are also possible. Beyond these, new developments in electronics make possible entirely new synthesis devices and suggest new approaches to older unsolved problems. As one example, digital control of analog synthesis based on a microprocessor approach makes it possible to realize musical structures and developments of a greater complexity than is possible with manual control alone. As a second example, charge‐transfer analog shift registers provide, analog delay in a compact and inexpensive form, thus making possible new approaches to special musical effects, reverberation, and pitch extraction, to name a few.
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Electronic synthesis models of acoustic instruments (A)

D. A. Luce

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S1-S1 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Combining correlative analysis of acoustic musical instrument sounds with basic physical properties leads to functional models for electronic synthesis. Determination of the number of degrees of freedom and their ranges associated with psychoacoustically important parameters is crucial for efficient models. Derivation of three models for the trumpet, violin, and French horn and simulative synthesis examples will be presented.
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Hybrid sound synthesis (A)

M. V. Mathews

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S1-S2 (1977); (2 pages)

Online Publication Date: 11 Aug 2005

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Most general purpose digital computers are not fast enough to directly compute musically sophisticated sound waves in real time. A hybrid system in which a computer controls an analog synthesizer can generate interesting sounds in real time. The computer supplies three main services. It senses the gestures of the performer. It provides a memory for storing these gestures as time functions. It computes the time functions which control the synthesizer as a complex combination of the real time gestures of the performer and the time functions in memory. The hybrid system is a good instrument with which to study the real time interactions between a performer, his instrument, and the sound he is producing. At present, the precision, quality, and range of timbres which can be obtained from a hybrid system are limited by the analog synthesizer. Shortly these limitations will be removed by replacing the analog device by a special purpose digital synthesizer.
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Contemporary uses of electronic music synthesizers in pop music (A)

Patrick Gleeson

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S2-S2 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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I will play taped excerpts from various recordings I have contributed to as a synthesizer player and arranger. The recordings span the period from 1970 to the present, by “charted” (top 200) artists, such as Jefferson Starship, Lenny White, Dr. Hook, Pablo Cruise, and Herbie Hancock. I will discuss each selection and in some cases will present the tracks in various special mixes which will make clear the role of the synthesizer. My general purposes are (1) to relate contemporary practice among pop recording artists; (2) to discuss certain limitations of contemporary instruments, emphasizing those that may be particularly interesting to the members of the Acoustical Society; and (3) to point out some unexplored directions which might be taken for users of this wonderful musical instrument.
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Performance values in studio realizations of electronic music (A)

W. Carlos and R. Elkind

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S2-S2 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Working techniques and philosophy for our particular approach in producing electronic music recordings will be discussed. The studio facility will be discussed, particularly its unique features. An example of a typical complex musical passage will be played in component and find forms. We also will attempt to cover several mixing situations in which both quad and stereo “imaging” may be made to simulate that of a natural acoustic environment.
back to top Session B. Physiological Acoustics I: Acoustical Properties of the Ear
Contributed Papers
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Cochlear distortion‐products: effects of altering the organ of Corti (A)

J. H. Siegel, D. O. Kim, and C. E. Molnar

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S2-S2 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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We have extended the cat studies of Kim and Molnar [Neuroscience Abstracts Vol. II, 1976] to the chinchilla with normal or altered organ of Corti. As in the cat, propagated distortion‐products (f2−f1) and (2f1−f2) are strongly present in responses of normal chinchilla cochlear‐nerve fibers. Exposure of chinchillas to a 4 kHz octave‐band noise at 108 dB SPL rms for two hours produced destruction of the organ of Corti in the basal two‐thirds of the cochlea. Two‐tone pairs with f1=3680 Hz and f2=4000 Hz, corresponding to the damaged region, produced no measurable propagated distortion‐products; two‐tone pairs with lower frequencies corresponding to the undamaged region produced large propagated distortion‐products. In normal chinchillas, brief (1–2 min) exposure to an 80–90 dB SPL single‐frequency fatiguing‐tone, similar in frequency to the two‐tone pairs, led to a temporary reduction, by more than half, of the amplitude of the propagated distortion‐products; recovery was complete in a few minutes. We conclude: (1) Propagated distortion‐products are generated in the cochlear region where both primary components are large, and then mechanically propagated apicalward like externally applied single tones; (2) even delicate and reversible alterations of the organ of Corti can affect the strongly‐nonlinear behavior of the motion of the cochlear partition. [Work supported by NIH Grants NS07498, RR00396, NS07057, and NS00162.]
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Cochlear‐distortion products: inconsistency with linear motion of the cochlear partition (A)

D. O. Kim, J. H. Siegel, and C. E. Molnar

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S2-S3 (1977); (2 pages)

Online Publication Date: 11 Aug 2005

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Under two‐tone stimulation at frequencies f1 and f2 (f1<f2), the phase‐locked response of a cochlear nerve fiber is composed predominantly of distortion‐products (f2−f1) or (2f1−f2) when these distortion frequencies are near the characteristic frequency of the nerve fiber. We have concluded (H1) that the distortion‐product is generated in a more basal region and propagated apically to the characteristic place of the distortion frequency. An alternative hypothesis (H2) postulates that the distortion‐product is generated locally near the characteristic place of the distortion frequency, and that a “second filter” passes the distortion frequency but blocks frequencies f1 and f2. With f1=3680 Hz and f2=4000 Hz, at 50 dB SPL, we have found strong (f2−f1) from fibers with characteristic frequencies near 320 Hz. In noise‐damaged cochleas [Siegel et al., Abs. No. B1], where histological and physiological examinations show damage in the basal region but no damage in the 320‐Hz region, interpretation of the absence of the (f2−f1) response in accordance with H2 would require that (1) in normal cochleas, the stimulus frequencies f1 and f2 must propagate to the 320‐Hz region; and (2) noise damage to the organ of Corti in the basal region must interfere with this propagation f1 and f2 to the 320‐Hz region. Accepted theories of cochlear mechanics support the propagation of distortion‐products as required by H1 but do not support the above two requirements needed for H2. [Work supported by NIH Grants NS07498, NS00162, RR00396, and NS07057.]
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Acoustic properties of the interaural pathway in the chicken (A)

J. J. Rosowski

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S3-S3 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The acoustic transmission properties of the avian interaural pathway were measured in the chicken with a sound probe placed within the middle ear. Ten chickens, 3–9 days old, were anesthetized, both external meati were surgically excised, the animal was placed in a head holder, and sound tubes with associated probe microphones were sealed over the right and left tympanic rings. The left middle ear was opened, and a 1‐mm‐diam sound probe was placed in the middle ear. The ear was then resealed. Continuous pure tone stimuli of approximately 110 dB SPL and of various frequencies was presented first to one ear and then to the other. With each stimulus presentation SPL was measured at three places: the stimulated external ear, the opposite external ear, and in the middle ear. A reduction in SPL of 25–30 dB was noted in the left middle ear regardless of whether the left or right external ear was stimulated. These observations suggest that the interaural pathway imposes no attenuation on transmitted sound at frequencies within the audible range of the chicken. The importance of the interaural pathway in avian hearing has yet to be determined. [Work supported by NSF.]
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Relationship between loudness discomfort level and the acoustic reflex threshold for normal and sensorineural ears (A)

H. L. McLeod and H. J. Greenberg

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S3-S3 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The relationship between loudness discomfort level (LDL) and the acoustic reflex threshold (ART) was determined by comparing the ART to LDL obtained by the psychophysical method of constant stimuli. Prerecorded, randomly selected stimuli of 1000 Hz, 2000 Hz, and a multitalker speech noise were presented to normal and sensorineural hearing‐impaired listeners. Both LDL and ART were found to be significantly higher for the hearing‐impaired group. In addition, LDL for the hearing‐impaired group consistently fell below the ART. Significant differences were shown to exist between mean LDL and ART thresholds. However, contrary to previous research [A. Olsen and N. Hipskind, J. Aud. Res. 13, 71–76 (1973)] a multiple regression analysis indicated highly significant correlations between LDL and ART. The ability of each dependent variable to predict the presence or absence of a hearing loss is included with a discussion of the dangers involved in using ART data to predict the LDL.
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Decay of the acoustic reflex during steady‐state and intermittent noise exposures (A)

R. Hétu and P. U. Careau

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S3-S3 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Acoustic‐reflex activity was continuously monitored by measuring change in the acoustic impedance at the eardrum for seven normal‐hearing young adults under three temporal patterns of exposure to a broadband noise: one steady‐state condition of 16 min duration at 105 dBA and two intermittent conditions of 32 min total duration with sound levels alternating between 105 dBA and quiet every 1 or 4 min, depending upon the condition. It was found that after 16 min of actual noise exposure, acoustic‐reflex response decreased to 40% of initial magnitude under the steady‐state and the 4‐min on—off conditions. Under both intermittent conditions, progressive decrease of on‐response following onset of successive noise bursts showed that quiet periods allowed only partial restoration of initial reflex excitability. Under the 4‐min on–off condition, it was observed that the contractile strength of the middle ear muscles recovered to the level observed for equivalent exposure times under the 1‐min on—off condition; however, during the third minute of the, 4‐min bursts, it decreased to the level observed under the steady‐state noise condition for equivalent cumulative exposure time.
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Influence of alcohol on the acoustic reflex and temporary threshold shift (A)

M. S. Robinette and R. H. Brey

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S3-S3 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Blood alcohol levels between 0.09% and 0.15% were found to reduce the protective action of the acoustic reflex in five normal hearing human subjects. Specifically, acoustic reflex thresholds were raised, reflex magnitude decreased, and TTS increased under alcohol conditions. Stimuli consisted of a narrowband noise (500–1000 Hz) and a 500‐Hz pure tone. Measurements were made at blood alcohol concentrations from 0.05% to 0.15%. TTS at 1000 Hz was determined three minutes following a 10‐min exposure of narrowband noise at −5, +5, and +20 dB relative to the subject's pre‐alcohol acoustic reflex threshold. [Work supported by NIH.]
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On the input acoustic admittance of the human middle‐ear (A)

W. M. Rabinowitz

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S3-S3 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A method for obtaining the acoustic admittance (or impedance) at the eardrum of normal human ears is discussed. Its validity is demonstrated for frequencies up to 4 kHz. Special attention is given to estimating the earcanal space between the eardrum and the tip of the electroacoustic probe hermetically sealed in the earcanal; admittance measurements with earcanal static pressures of +40 and −40 cm H2O (re ambient) are used. However, in contrast to the usual assumption applied in clinical measurements, we do not assume that these static pressures reduce the (middle‐ear) admittance at the eardrum to zero. Results are reported for four subjects. Below 500 Hz, the eardrum admittance is compliance dominated. From 1 to 4 kHz, the resistive component of the eardrum impedance exceeds the reactive component. Furthermore, a local increase in eardrum resistance is observed near 2 kHz; this may reflect the influence of the middle‐ear cavity resonance [J.J. Zwislocki, J. Acoust. Soc. Am. 34, 1514–1523 (1962)]. Implications of the results for earphone couplers are discussed. [Work supported by NIH.]
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Growth of right ear advantage following callosal section in an adolescent (A)

M. L. Lenhardt

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S3-S3 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Material previously reported to the Society (92nd meeting, Abs. No. WW3) described a thirteen year old boy's performance prior to and post surgical section of his corpus callosum on dichotic CVs (provided by Kresge, LSU). Pre‐operatively, no ear advantage was observed. After section, a clear right ear superiority emerged. Correct performance almost doubled for the right ear, whereas the left ear performance dropped to chance level. The error pattern did not vary after surgery. Prior to section only a few “double corrects” were reported for dichotic stimulation. This may have been influenced by the anxiety of the upcoming surgery. Initial post surgical testing revealed no “double corrects.” Present data, approximately 10 months later, revealed an increase in “double corrects,” as well as in ear advantage and performance. Data on time‐staggered CVs suggested a changing information processing situation. Implications of the data will be discussed.
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Occluded ear simulators (A)

M. D. Burkhard and J. C. Zuercher

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S4-S4 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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With the aid of a computer program, accurate models of acoustical elements were used to study and investigate both the Zwislocki‐type ear simulators and proposed alternative designs. An occluded ear simulator is the part that remains adjacent to the eardrum when an earmold is inserted into the ear and, in most designs, contains the acoustic networks that establish an equivalent eardrum impedance. The designs were optimized using parametric methods. This led to a better understanding of Zwislocki‐type four‐resonator structures for simulating real ear eardrum impedance and also to the design of a new two‐resonator construction. The agreement between the ear simulator designs (both theoretical and experimental) with available data on ears is discussed. Tentative electrical analog values of constants for the resonators of the new design are as follows: Resonator 1: resistance 1030 ω, compliance 0.13 μF, and inertance 0.16 H. Resonator 2: resistance 300 ω, compliance 0.34 μF, and inertance 0. 0043 H. The canal portion of the occluded ear simulator is a cylinder 12.7 mm long and 7.5 mm in diameter. The external diameter is 19.4 mm. The design avoids placement of resistance elements in the canal simulation portion which would prevent its use for experiments that might require access to this region.
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External and middle ears, the determinants of the auditory threshold curves (A)

S. M. Khanna and J. Tenndorf

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S4-S4 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The pressure transformation ratio of the cat's ear under auditory free‐field conditions was calculated from Nedzelnitzky's data [pressure in scala vestibuli (sc. v.) for a constant SPL at the tympanic membrane] with appropriate corrections applied for his open bulla and the tympanic membrane reference. For a constant SPL at the pinna, the pressure in sc. v. followed a curve identical to an inverted plot of the cat's free‐field threshold. Therefore, when expressed in terms of threshold SPLs at the pinna, the pressure in sc. v. became independent of frequency, its absolute value being 0. 003 dyn/cm2. These results demonstrate the importance of the acoustic properties of ear canal and pinna. They also suggest that the free‐field threshold curve is mainly determined by properties of the external and middle ears, including the inner‐ear input impedance. The power entering the inner ear at threshold was calculated from cat impedance data of Lynch and Peake. Its value is about 10−18 W for frequencies between 50 and 7000 Hz. [Supported by NIH grants.]
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Dual processes for loudness (A)

W. H. Atkinson

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S4-S4 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A body of anatomical, electrophysiological, psychophysical, and behavioral research supports the proposition that there is a division in audition similar to the rod/cone dichotomy in vision. Evidence will be presented for the presence of discrete processes for low and high intensity sounds. Both can be identified in electrophysiological measurements at all levels of the auditory nervous system. Both processes can also be discerned in magnitude estimates of loudness. If subjective loudness is plotted as a function of the cube root of sound pressure, the curve consists of two linear sections with a discontinuity of slope at approximately 65 dB SPL. Both segments are present for frequencies up to at least 3 kHz. Linearity is preserved in the presence of a masking noise but the variation in slope and intercept constants suggests the operation of different mechanisms of masking for each process.
back to top Session C. Physiological Acoustics I: Deafness, Audiometry
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Remote audiometric testing via telephone: the design of a digitally controlled audiometer (A)

A. Yonovitz, C. W. Mitchell, and J. Lozar

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S4-S4 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The acquisition of pure tone and speech audiometric data from a remote location would be especially useful in schools, industrial applications, military usage, physicians' practices, and hospital‐medical‐center environments. Data transmission using standard ASCII encoding (with RS‐232c interface) provide an efficient means of controlling the acoustic parameters in audiometric testing. Essentially, in a digitally controlled audiometer, the devices receive and transmit control commands at a 300 baud rate readily compatible with available computer hardward interfaces. Unique design concepts including simultaneous use of the acoustic coupler modes for speech and data transmission are discussed. Using FSK coding techniques the ordinary telephone system may be employed to remotely relate audiological diagnostic information between two locations.
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Low‐frequency hearing loss: perception of filtered speech, psychophysical tuning curves, and masking (A)

Aaron R. Thornton and Paul J. Abbas

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S4-S5 (1977); (2 pages)

Online Publication Date: 11 Aug 2005

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Two subjects with low‐frequency hearing loss were evaluated to determine whether their responses to low‐frequency stimulation might be a result of stimulation of nerve fibers with higher characteristic frequencies. One subject showed large low‐frequency threshold shifts in the presence of high‐pass noise or a 2000‐Hz tonal masker. Psychophysical tuning curves for 500‐ and 800‐Hz probe signals were peaked above 2000 Hz. This subject was also tested with high‐pass, low‐pass, and unfiltered speech both in quiet and in the presence of a high‐pass noise masker. Results were interpreted as showing relatively little encoding of low‐frequency speech by high‐frequency nerve fibers. The second subject had masking patterns and psychophysical tuning curves which were most consistent with detection of low‐frequency signals by nerve fibers with low characteristic frequencies. Psychophysical tuning curves of both subjects were compared to those obtained from subjects with high‐frequency hearing loss. Implications for the diagnosis of low‐frequency hearing loss and the use of hearing aids are discussed. [Work supported by NIH.]
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Categorizing hearing loss from speech recognition data (A)

Edith L. R. Corliss and Elizabeth F. Moore

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S5-S5 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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During the National Health Survey of 1971–1973, pure‐tone threshold measurements were made for octaves from 500 to 4000 Hz. At the same time, subjects were presented with lists of test sentences, and scores were kept identifying the individual words missed. Initial presentation of the test material was keyed to the subject's hearing level at 1000 Hz, and if more than a few words were missed, the level of successive test lists was raised in 10‐dB increments until a high score was achieved or the maximum level of 80 dB for the list presentation was reached. By classifying the individual phonemes of each word and grouping the test results for each list, growth functions for intelligibility were derived for each ear of every subject who received more than a single list for each ear. The results show distinct groupings of slope of growth function and intercept along the level of list presentation, separating classic cases of “recruitment,” sensorineural loss, and conductive losses. The categorization permitted separate consideration of low‐frequency, midfrequency, and high‐frequency losses.
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Development of a clinical procedure for assessment of auditory localization (A)

W. G. Cook and T. Frank

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S5-S5 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A clinical test of auditory localization ability was administered to 45 normal hearing subjects. The subjects were seated in the center of a circular array of seven ceiling‐mounted speaker assemblies. They were required to identify the speaker through which each of a series of 24 presentations of the stimulus “where is this?” was directed. The localization test was performed employing three stimulus presentation levels of 5, 10, and 15 dB SL, re sound‐field SRT, and three speaker placements which had radii of 2′7″, 4′, and 5′ from the center of the audiometric test booth. Localization ability improved as the presentation level and speaker placement increased, reaching a maximum mean score of 76% at 15 dB SL and a 5′ speaker radius. The results agreed with previous findings [F. Malpica, M.S. paper (Penn State, 1976) (unpublished)] but did not agree with the results obtained in the initial Investigation of this localization test [G. R. Bienvenue and B.S. Siegenthaler, J. Speech Hear. Disord. 39, 469–477 (1974)].
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Role of the acoustic reflex in the acquisition of temporary threshold shift (A)

C. C. Olsen and J. F. Brandt

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S5-S5 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Acoustic reflex responses were monitored during the presentation of fatiguing stimuli in a temporary threshold shift (TTS) experimental paradigm. This method yielded a measure of TTS and a record of acoustic reflex activity elicited by the fatiguing stimuli. The fatiguing stimuli were interrupted and continuously presented octave noise bands (500–1000 and 1500–3000 Hz) presented at 98 dB SPL. Test frequencies for the low and high band‐pass noises were 1500 and 4500 Hz, respectively. Noise exposure conditions having shorter off‐times produced significantly more reflex activity over time than did exposures having longer off‐times. In addition, greater impedance changes were elicited by the high‐band noise exposure than by the low‐band exposure. Though the high‐band noise exposure provided greater reflex activity it also produced significantly more TTS than did the low‐band noise. Differences in the amount of TTS produced by the two noise bands could not be attributed to the effects of acoustic reflex contraction. It may be that under certain stimulus conditions the acoustic reflex plays no role in the acquisition of TTS.
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Complex tonal perception through hearing aids (A)

L. S. Bowling, H. C. Schweitzer, and G. D. Causey

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S5-S5 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The influence of nonlinear distortion in hearing aids on three tone complex perception was evaluated in a comparison paridigm requiring a Same/Higher/Lower pitch judgment. Thirty normal‐hearing subjects listened to recordings of the simultaneous tones 888, 1000, and 2140 Hz processed by two hearing aids and the hearing‐aid test system alone. A comparison signal differed only in the center frequency, which was varied over a 40 Hz range. Hearing‐aid—generated non‐linear distortion improved the accuracy of the same judgments. The evidence of confusion errors for the Higher and Lower stimuli were significantly greater for the low‐fidelity conditions. Cubic difference tones (CDT), identified in the hearing‐aid outputs, appeared to relate to the direction of the listener confusions. The results for the two hearing aids were essentially the same in spite of substantial difference in amounts of nonlinear distortion. [Work supported by VA.]
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Auditory handicap of hearing impairment and the limited benefit of hearing aids (A)

R. Plomp

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S5-S5 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The aim of this paper is to promote a better understanding of hearing impairment as a communicative handicap, primarily in noisy enviornments, and to explain the essentially limited applicability of the hearing aid. From available data we can conclude that about 7.5% of the population is auditory handicapped, with a hearing loss for speech ⩾ 24 dB. Every hearing loss can be interpreted as the sum of a loss class A (Attenuation), characterized by a reduction of the levels of both speech signal and noise, and a loss class D (Distortion), comparable with a decrease in speech‐to‐noise ratio. On the average, the hearing loss of class D (= hearing loss in noise) appears to be about one‐third (in dB) of the total hearing loss (A + D = hearing loss in quiet). A hearing aid can compensate class‐A hearing losses, giving difficulties primarily in quiet, but not class‐D hearing losses, giving difficulties primarily in noise. The latter class represents the first stage of auditory handicap, beginning at an average hearing loss of about 24 dB. An algorithm for computing speech level relative to speech‐reception threshold as a function of hearing losses of classes A and D, as well as acoustic gain, internal noise, and quality of the hearing aid, has been developed and examples will be given.
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Rate of convergence in adaptive fitting of wearable master hearing aid (A)

Harry Levitt, Judy R. Dubno, Lisa Freeman, and Ronald Slosberg

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S5-S6 (1977); (2 pages)

Online Publication Date: 11 Aug 2005

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In many adaptive strategies the rate of convergence is, on the average, greatest at the start of testing and gradually fails to zero as the target is approached. Preliminary data on the adaptive fitting of a wearable master hearing aid show the same trend. In particular, the rate of improvement in the subjects' performance (on a nonsense syllable test) was found to be greatest, on the average, during the first test session and then tapered off rapidly during subsequent test sessions. Considering the cost of extended testing, an important practical question is when to terminate testing. The implications of different stopping rules in the adaptive fitting of hearing aids will be discussed. [Research supported by Contract No. NIH‐NO1‐NS‐4‐2323 from the National Institute of Health.]
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Influence of hearing aid nonlinear distortion on closed set intelligibility performance in noise (A)

H. C. Schweitzer and M. T. Howard

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S6-S6 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Two hearing aids of highly similar electroacoustic characteristics except for notable differences in nonlinear distortion were used in a study of speech intelligibility. Bandpass filtering provided further assurance of electroacoustic homogeneity. New recordings of Modified Rhyme Tests (MRTs) were recorded through these hearing aids in the presence of speech spectrum noise. Signal‐to‐noise ratio at the input to the hearing aids was +3 dB. Thirty normal‐hearing young adult listeners gave written responses on the six‐foil closed‐set intelligibility test. Despite substantial differences between the aids for both harmonic and intermodulation distortion, no differences on intelligibility were obtained. Mean performance was 2% better for the aid with the higher distortion but the t score was non‐significant. [Work supported by VA.]
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