From: malcolm@interval.com (Malcolm Slaney)
Date: Mon, 19 Feb 1996 22:12:23 -0800
Subject: Hearing Aids (4:15PM on Thursday) !!!!
Message-Id: <v02130500ad4f0fe2d7e0@[199.170.108.19]>
This week Chas Pavlovic from Resound will be talking about his company's
hearing aid technology. Again, because of extenuating circumstances, this
seminar will be at 4:15PM on Thursday afternoon!
One topic that we've been delinquent in covering is hearing aids. Hearing
aids are, without a doubt, the biggest commercial application of auditory
principles. What can be done? What do we know about the psychacoustics of
hearing loss? How can we fit the available technology to individual's
hearing loss? As we all grow older, this is a technology that will affect
a large percentage of us.
Most hearing aid advertisements don't include any technical details. They
are very high tech, yet most customers are relatively unsophisticated.
Here's our chance to find out the real story behind today (and tomorrow's)
hearing aids.
Chas Pavlovic is the Vice President of engineering at Resound. Resound is
a local company that makes one of the more technologically advanced
devices.
Who: Chas Pavlovic (ReSound)
What: Hearing Aid Technology at ReSound
When: Thursday February 22 at 4:15 PM <=== Note time!!!
Where: CCRMA Library (Top Floor of the Knoll at Stanford)
I've attached a brief synopsis of Chas' talk, and a list of his recent
publications in the area.
Come see the latest in Hearing Aid technology! ReSound has a state-of-the
art product. A talk later this spring by Bill Yund (VA-Martinez) will
cover advanced research on multi-band aids.
-- Malcolm
Hearing Aid Technology at ReSound
Chas Pavlovic
V.P. at Resound Corporatioon
Brief Synopsis: Psychoacoustic aspects of hearing loss and and their
implications towards hearing aid designs, ReSound's processing versus the
rest of the industry's, current research at ReSound on matching hearing aid
settings to specific hearing losses.
ReSound's hearing devices incorporate technology initially designed at AT&T
Bell Laboratories. The unique sound processing is called "Multiband Full
Dynamic Range Compression" (MBFDRC). After a front-end AGC, sounds are
split into two bands, each processed by a syllabic compressor. The design
of these compressors is unique in three important aspects: The thresholds
are low (45 dB SPL); the dynamic range compression operates over a wide
range (40dB: from 45 to 85 db SPL); and the compression ratio is
programmable in eleven steps, from linear to 3:1 compression. This design
allows the frequency response to adjust itself automatically in response to
changes in both bass and treble sound intensities. The processing can be
programmed to match the patient's loudness contours. The resulting benefit
is improved intelligibility, as shown by Villchur (1973) and Moor et al.
(1992).
1. Hou Z; Pavlovic CV.
Effects of temporal smearing on temporal resolution, frequency
selectivity, and speech intelligibility.
Journal of the Acoustical Society of America, 1994 Sep, 96(3):1325-40.
(UI: 95052032)
Abstract: Envelopes of speech were smeared in 23 parallel frequency channels.
The smeared speech was presented to normal-hearing listeners, and the
effects of different smearing magnitudes on speech intelligibility were
measured by obtaining speech recognition scores. It was demonstrated
theoretically and experimentally that the system consisting of the computer
smearing and the auditory system had reduced temporal resolution but nearly
normal frequency resolution. Speech intelligibility of the processed
vowel-consonant nonsense syllables was tested for low- and high-pass filter
conditions. The overall speech recognition scores as well as the
recognition scores of the consonants grouped according to articulatory
features were analyzed. The results indicated that smearing with a narrow
temporal window did not degrade speech. The larger equivalent rectangular
durations (ERDs) of the resultant temporal window (RTW) of the combined
system (temporal smearing plus auditory system) produced a small but
significant reduction in speech intelligibility for the low-pass filter
condition. Scores for the RTWs > 16 ms were significantly different from
the score for the 7.7-ms RTW for the high-pass filter condition, but this
effect was small and did not differ across articulatory features.
2. Pavlovic CV.
Band importance functions for audiological applications.
Ear and Hearing, 1994 Feb, 15(1):100-4.
(UI: 94252481)
Abstract: Recently, band importance functions have been developed for a number
of speech tests used in audiology. These functions, as well as the
importance functions for average (everyday) speech, are also being
considered for the inclusion in the revised Articulation Index standard
(submitted for vote to the Acoustical Society of America). In this paper,
the band importance functions for different speech materials (usually
reported in literature for 1/3 octave bands) have been recalculated to
correspond to frequency bands normally used in audiological applications.
In addition, criteria for selecting appropriate importance functions and
transfer functions are discussed.
3. Bentler RA; Pavlovic CV.
Addendum to "transfer functions and correction factors used in hearing aid
evaluation and research".
Ear and Hearing, 1992 Aug, 13(4):284-6.
Pub type: Journal Article; Review; Review, Tutorial.
(UI: 93012582)
Abstract: In an earlier publication, various transformations used in hearing
aid research and its application were summarized. As a result of continued
interest and requests, additional transfer functions are provided in this
addendum.
4. Purdy SC; Pavlovic CV.
Reliability, sensitivity and validity of magnitude estimation, category
scaling and paired-comparison judgements of speech intelligibility by
older listeners.
Audiology, 1992, 31(5):254-71.
(UI: 93080504)
Abstract: This study investigated the reliability, sensitivity, and validity of
speech intelligibility judgments for hearing aid evaluation. Subjects aged
60-87 years judged the intelligibility of sentences using either magnitude
estimation, category scaling or paired comparisons. The 60+ age group was
chosen as representative of the majority of hearing aid wearers. Speech
recognition scores for Central Institute for the Deaf (CID) sentences and
Northwestern University Auditory Test No. 6 (NU-6) words were also
obtained. The speech was bandpass filtered using filter settings that
produce a monotonic increase in predicted intelligibility based on
articulation index theory. Speech recognition scores and intelligibility
judgments were obtained for each of eight filter conditions. Test-retest
reliability was poorest for paired comparisons and CID sentence scores.
There were no differences in sensitivity among the three psychophysical
procedures. Intelligibility judgments and NU-6 scores were more sensitive
than CID sentence scores to differences among conditions. The results
indicated that intelligibility judgments are valid measures of speech
recognition.
5. Pavlovic CV; Rossi M; Espesser R.
Use of the magnitude estimation technique for assessing the performance of
text-to-speech synthesis systems.
Journal of the Acoustical Society of America, 1990 Jan, 87(1):373-82.
(UI: 90131394)
Abstract: As text-to-speech systems develop, it becomes necessary to compare
various solutions and to evaluate whether a change in the synthesis
procedure has an effect on the listener's attitude to the system. The
possibility of directly scaling intelligibility, naturalness, and user's
satisfaction (i.e., acceptability) with the magnitude estimation technique
is investigated. A magnitude estimation protocol suitable for this purpose
is described. In general, within the limits of the methodological
constraints discussed in this paper, the procedure appears to be reliable
and valid for quantifying the perceived attributes of synthesized speech.
6. Pavlovic CV.
Speech intelligibility considerations in specifying characteristics of a
programmable hearing aid.
Acta Oto-Laryngologica. Supplement, 1990, 469:181-9.
(UI: 90289563)
Abstract: With the use of sophisticated speech processing techniques in
auditory prosthetic devices, it will be possible to convert the speech
signal to maximal satisfaction for the user. However, the user's
satisfaction is a multidimensional percept that may include speech
naturalness, intelligibility, pleasantness, etc. This paper discusses the
place of speech intelligibility considerations in the ensemble of criteria
that could be associated with these perceptual attributes. It also
discusses some of the problems that may be responsible for the relative
inadequacy of the available speech intelligibility prediction procedures
for use in digital hearing aids.
7. Bentler RA; Pavlovic CV; Abbas PJ.
A signal processing scheme for output limitation.
Acta Oto-Laryngologica. Supplement, 1990, 469:230-5.
(UI: 90289571)
Abstract: For both normal listeners and mild to moderately sensori-neurally
impaired (probable etiology, presbycusis) listeners a summation of
discomfort (S) occurs for complex stimuli, proportional to the logarithm of
the number of components. Regression equations of S = 2.05 + 11.51 log n
for normals and S = 3.95 + 12.88 log n for hearing impaired (where n equals
the number of components or bandwidth in the complex) were found to be
significantly different. This change in percept with increased bandwidth
(or components) has not been satisfactorily explained in terms of power or
amplitude peak density of the stimuli. The regression equations could be
applied to future digital hearing aids so that maximum output levels (MPO)
would account for this summation.