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Re: AUDITORY Digest - 11 Jul 2002 to 12 Jul 2002 (#2002-107)



Dear Lars,

Masking is composed of two components, and in some sense, they are very
dissimilar.
First there is the cochlear compression component, which is not really
masking in the sense you are speaking of. It is more a cochlear gain factor,
that has to do with the "agc" dynamic range control within the cochlea.
This controls the level into the neurons.

The second is the true masking due to "neural noise." This is the true
masking
effect, where two signals cannot be separated, because the distributions of
detection overlap.

The hearing impaired lose the first component, but everyone has the second,
as long as they have a brain. ;-)

Nice question.

   --Jont Allen

Refs:
Here are some references that discuss this in detail, and I would be happy
to send links to the eprints of these articles, to anyone who asks:

author = {Allen, J.B.}
,title={Psychoacoustics}
,booktitle = {Wiley Encyclopedia of Electrical and
       Electronics Engineering}
,volume = 17
,editor={Webster, J.G.}
,publisher={John Wiley \& Sons, Inc}
,address={New York, NY}
,pages = {422-437}
,year = {1999}

,author={Allen, J.B.}
,title={Amplitude compression in hearing aids}
,booktitle={MIT Encyclopedia of Communication Disorders}
,publisher={MIT Press}
,year=2002
,editor={ R.~Kent }
,chapter={ To appear }
,pages={}
,address={MIT, Boston Ma}

author={Allen, J.B.}
,title={Nonlinear Cochlear Signal Processing}
,booktitle={ Physiology of the Ear, Second Edition }
,publisher={Singular Thomson Learning}
,year=2001
,editor={ Jahn, A.F. and Santos-Sacchi, J.}
,chapter={19}
,pages={393--442}
,address={ 401 West A Street, Suite 325 San Diego, CA 92101 }

Date:    Fri, 12 Jul 2002 12:53:17 +0200
From:    =?iso-8859-1?Q?Lars_Bramsl=F8w?= <LAB@OTICON.DK>
Subject: Bit-rate reduced audio and hearing loss

Dear list,

The modern audio compression techniques (MPEG, MP3, WMF etc..) can =
easily
provide transparent audio quality if the bit-rate is sufficiently high, =
e.g.
256 kbit/s.  They are based on more or less advanced hearing models and
exploit the temporal and spectral masking properties of the ear to keep =
all
quantization errors below the masked thresholds.

If these sounds are used with hearing impaired subjects and hearing =
aids,
one could speculate that either the nature of the hearing loss or the
hearing aid signal processing could potentially unmask the artefacts of =
the
compression.  One such example would be a ski-slope hearing loss with =
normal
LF hearing and severe HF hearing loss, combined with the appropriate
frequency shaping, leading to audible artefacts in the normal hearing
region.

On the other hand, we can expect that the spectral and temporal =
resolution
of the impaired ear is poorer than that of the normal ear.  So if the =
audio
quality is transparent to the normal-hearing listener it will also be
perceived as transparent by the hearing-impaired listener.

Does anyone have good or bad experiences with hearing aid users and =
bit-rate
reduced audio?

Regards,

Lars Bramsl=F8w

-----------------------------------------------------
Lars Bramsl=F8w
Ph.D., M.Sc.E.E.
Audiology

Oticon A/S
Strandvejen 58
DK - 2900 Hellerup

phone:  +45 39 13 85 42
fax:            +45 39 27 79 00

mailto:lab@oticon.dk
http://www.oticon.com
-----------------------------------------------------

------------------------------

Date:    Fri, 12 Jul 2002 13:33:44 +0200
From:    alexander lerch <lerch@ZPLANE.DE>
Subject: Re: Bit-rate reduced audio and hearing loss

Hello,

there was a MP3-Listening Test of the german c't-magazine
published in issue 6/2000
(http://www.heise.de/ct/00/06/092/default.shtml, in german).

The listener with the "best" differentiation between original
and coded signals turned out to be hearing impaired
(siginificant hearing loss above 8kHz).

However, I would not claim this test to be scientific relevant.

Regards,
Alexander

Lars Bramsl°w schrieb:

Dear list,

The modern audio compression techniques (MPEG, MP3, WMF etc..) can easily
provide transparent audio quality if the bit-rate is sufficiently high, e.g.
256 kbit/s.  They are based on more or less advanced hearing models and
exploit the temporal and spectral masking properties of the ear to keep all
quantization errors below the masked thresholds.

If these sounds are used with hearing impaired subjects and hearing aids,
one could speculate that either the nature of the hearing loss or the
hearing aid signal processing could potentially unmask the artefacts of the
compression.  One such example would be a ski-slope hearing loss with normal
LF hearing and severe HF hearing loss, combined with the appropriate
frequency shaping, leading to audible artefacts in the normal hearing
region.

On the other hand, we can expect that the spectral and temporal resolution
of the impaired ear is poorer than that of the normal ear.  So if the audio
quality is transparent to the normal-hearing listener it will also be
perceived as transparent by the hearing-impaired listener.

Does anyone have good or bad experiences with hearing aid users and bit-rate
reduced audio?

Regards,

Lars Bramsl°w


--
dipl. ing.
alexander lerch

zplane.development
http://www.zplane.de
holsteinische str. 39-42
D-12161 berlin
fon: +49.30.854 09 15.0
fax: +49.30.854 09 15.5

------------------------------