Study report SoundSmoothing - Siemens Hearing Instruments

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Study report
SoundSmoothing
Despite such modern features as multichannel, wide dynamic range compression (WDRC),
output limiting and noise suppression, many hearing instrument users still report discomfort
from common transient noises like paper rustling or clattering dishes (Hernandez et al., 2006).
In keeping with the company‘s innovative, user-oriented philosophy, Siemens has developed
SoundSmoothing®, an algorithm that substantially reduces impulsive, non-speech sounds. Recently,
the National Acoustic Laboratories (Australia) conducted an interesting and significant
clinical study to evaluate the effects of this new algorithm (O'Brien et al., 2006).
SoundSmoothing: How it works
After a spectro-temporal analysis of the microphone signal, envelope features are extracted. These
are then used to determine whether speech or non-speech sounds are present. To accomplish
this, the envelope features are analyzed using a speech model. Then an attenuation factor is
calculated for non-speech sounds only. The amount of transient gain modification is determined
by the ratio of peak level to long-term overall RMS level (i.e. the more transient, the more gain
reduction).
Fig. 1 Algorithmic implementation of SoundSmoothing
Objectives
The objectives of this study were to determine if:
• SoundSmoothing provides a noticeable benefit to hearing aid users when listening to
transient noises.
• SoundSmoothing negatively affects speech perception and / or the horizontal localization
of sounds containing transients.
Evaluation of a transient noise reduction algorithm
Josef Chalupper and Beate Krämer
Corporate Audiology, Siemens Audiologische Technik GmbH, Germany
Speech model
Input Spectro-temporal Extraction
Detection Transient gain Resynthesis Output
analysis
of envelope of non-speech modification
features
components

Methods
21 hearing-impaired subjects ranging in age from 24
to 85 years, with a median age of 75, participated in
the study. All subjects had a symmetrical sensorineural
hearing loss. The mean three-frequency average
(3FA) hearing loss of the group ranged from 26 to
58 dB HL, with a mean 3FA of 43 dB HL. The subjects
had worn amplification devices from 1.5 to 21 years,
with a mean of 7.5 years. All subjects were fitted
binaurally with CENTRA P BTE housings containing
microphones and receivers. The signal processing
was done in an external computer. The devices were
fitted according to NAL-RP (Byrne et al.1991). Linear
amplification was chosen to separate the effect of
SoundSmoothing from other signal processing strategies
that adaptively change gain.
The SoundSmoothing algorithm could be disabled or
enabled on three strengths: minimum, medium, and
maximum. The algorithm was evaluated using six
stimuli comprising:
• Speech within two loud, repeated transient
sounds (door slamming and hammering nails)
• Speech within two softer sounds with frequent
amplitude fluctuations (paper rustling and cutlery
clattering)
• Speech within a medium level of stationary
sounds (party noise)
• Speech in quiet surroundings
In a round-robin paired-comparison test, the three
strengths and the “off” condition were compared
five times for speech in the door slamming, paper
rustling and quiet stimuli. For the remaining stimuli
only the medium strength and the ”off” condition
were compared. Each comparison was rated in terms
of preference strength (slightly better, moderately
better, or much better). For each stimulus, the
subjects were asked to indicate what subjective
listening criteria they had used to determine their
preference.
Horizontal localization performance was measured
using the hammering nails noise as stimulus. Horizontal
testing was conducted in an anechoic chamber
with an array of 20 loudspeakers. A 1.5-second
sample of the hammering nails noise was used as
the test stimulus. The subjects were asked to verbally
report the perceived direction of the stimuli.
”A strong preference for
SoundSmoothing can be seen
for all impulsive noises.“
Speech recognition was measured in the more continuous
paper rustling and cutlery clattering noises.
All three strengths as well as the ”off” condition
were included in these tests. For the speech discrimination
task, the Bamford-Kowal-Bench/Australian
version (BKB/A) Standard Sentence Lists (Bench et al.
1979) were administered.
Prior to testing, the subjects were asked to what extent
they were bothered by sudden sounds in their
everyday lives.
Results
Preference for SoundSmoothing
For simplification, the results of the various Sound-
Smoothing strengths were combined for each stimuli
– i.e. “on” setting comprises “min”, “med” and “max”.
A strong preference for SoundSmoothing can be
seen for all impulsive noises, especially for the loud
and repeated ones (hammering, door slamming).
A two-sided binomial test revealed statistically significant
preference for SoundSmoothing “on“ for
hammering (p < 0.001), door slamming (p = 0.007)
and paper rustling (p = 0.002). No preference can
be seen for the stationary party noise and the speech
signals. This is probably due to the fact that
SoundSmoothing does not affect these signals and
therefore the subjects did not hear any difference
between the “on” and “off” condition, yet the test
conditions forced the participants to choose between
them. Nevertheless, this is a very positive finding, as
it confirms that SoundSmoothing does not cause any
artifacts or interferences that would reduce speech
quality. Generally, the subjects used clarity of speech
as their main listening criterion in the paired comparison
test, although loudness and comfort of noise
rated higher (or equally high) when listening to
speech in the three most transient noises (door slamming,
hammering nails, and cutlery clattering).
Repeated measures ANOVAs on the weighted pairedcomparison
preference scores were calculated for
each stimulus, using grouping of the subjects by how
bothersome they found sudden sounds as the between-subject
variable. These analyses revealed no
significant effect of bothersomeness (p > 0.05). This
indicates that the degree to which sudden sounds
bother subjects in their everyday life is not a good
predictor of whether or not they will prefer Sound-
Smoothing for the stimuli used in the present study.
Horizontal localization
Horizontal localization was tested with the conditions
SoundSmoothing “on”, “off” and also with 10
hearing-impaired subjects in an unaided condition
(Keidser et al., 2006). The subjects reported no significant
effect of SoundSmoothing on horizontal
localization performance in the left/right dimension
(p = 0.33) or in the front/back dimension (p = 0.44).

Fig. 2 Preference for SoundSmoothing
Preference / %
100
80
60
40
20
0
Hammering Door
slamming
Fig. 3 Speech intelligibility in
noise with SoundSmoothing
SRT / dB SNR
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
Paper
SoundSmoothing off
SoundSmoothing min
SoundSmoothing med
SoundSmoothing max
Cutlery
Paper
rustling
Mean and 95% confidence intervals of speech reception
threshold (SRT); research conducted at the National Acoustic
Laboratories, Australia
SoundSmoothing "on" SoundSmoothing "off"
Cutlery
clattering
Speech Party
noise
Speech recognition
Speech discrimination testing was conducted in the
same anechoic chamber used for horizontal localization
testing, as described above.
The mean and 95% confidence intervals are shown
in Figure 3. The subjects needed a more favorable
(although still negative) signal-to-noise ratio to understand
50% of the speech signal in paper rustling
noise than in cutlery clattering noise. Analyses of variance
were performed on the signal-to-noise ratios
obtained for each noise using the SoundSmoothing
setting as a variable. There was no significant effect
of SoundSmoothing on speech recognition in paper
rustling (p = 0.65) or cutlery clattering (p = 0.97)
noises.
Percent of participants preferring
SoundSmoothing
”on” versus ”off” for
different sound samples
using a paired-comparison
procedure; research
conducted at the National
Acoustic Laboratories,
Australia

Conclusions
Although SoundSmoothing has its greatest effect on transient sounds with a high input level like door
slamming or hammering, the subjects preferred SoundSmoothing “on” for all transient noises, including
softer sounds with a frequent amplitude fluctuation (e.g. paper rustling, cutlery). There were absolutely no
indications that SoundSmoothing has any negative effects on speech recognition or localization. The new
CENTRA products are the first hearing instruments to be equipped with SoundSmoothing. It is expected that
SoundSmoothing will soon be a standard feature in many high-end hearing instruments.
References
O‘Brien, A., Keidser, G., Convery, E., Dillon, H. (2006).
Evaluation of a transient noise reduction algorithm.
NAL internal report: NAL011.
Hernandez, A. R., Chalupper, J., Powers, T. A. (2006).
An assessment of everyday noises and their annoyance.
The Hearing Review, 13(7), 16–20.
Bench, R. J., Doyle, J., Daly, N., Lind, C. (1979).
The BKB/A Speechreading (Lipreading) Test.
Victoria: La Trobe University.
Byrne, D., Parkinson, A., Newall, P., in:
Studebaker, G. A., Bess, F. H., and Beck, L. editors. (1991).
Modified hearing aid selection procedures for severe/profound
hearing losses: Parkton, MD.
York Press. p. 295–300.
Keidser, G., Rohrseitz, K., Dillon, H., Hamacher, V.,
Carter, L., Rass, U., Convery, E. (2006).
The effect of multi-channel wide dynamic range compression,
noise reduction, and directional microphone on horizontal
localisation performance in hearing aid wearers.
Int J Audiol., in press.
Siemens Audiologische Technik GmbH (2006).
SoundSmoothing: A new algorithm to reduce the annoyance
of noise.
Siemens
Audiologische Technik GmbH
Gebbertstrasse 125
91058 Erlangen
Germany
Phone +49 (9131) 308-0
www.siemens.com/hearing