# Re: Intelligibility of reversed speech, Why? (Jont Allen )

```Subject: Re: Intelligibility of reversed speech, Why?
From:    Jont Allen  <jba(at)RESEARCH.ATT.COM>
Date:    Thu, 25 Jan 2001 10:05:35 -0500

T=F3th L=E1szl=F3 wrote:

> On Thu, 25 Jan 2001, Ward Drennan wrote:

> > Acoustic information in speech is redundant, of course, but certainly=
,
> > as information (a cue of any sort) was removed or otherwise
> > blurred, you would expect the intelligibility to decrease for a given
> > S/N ratio.
> >
> No. Redundancy means that under a given condition (e.g. S/N ratio) you
> don't necessarily need ALL the cues for perfect comprehension. That is,
> you can remove some cues without decreasing intelligibility. However,
> under some other conditions the same cue may be vital.
> To put it another way: how can you tell that something you removed from
> the signal was or wasn't a cue? My point was that you cannot state this
> for sure from examining its effect under only one possible condition, p=
ut
> you have to examine all possible conditions.
> I hope this helps enlight my thinking.

I have another problem with the question of redundancy in speech.

It is clear there is redundancy in once sense. Language is an entropy con=
strained
code. If I say "the dog bit the c_t's tail" I doubt anybody would have tr=
ouble
telling me that the missing letter is "a." Thus speech is redundant.
QED

However I dont find the above to be very helpful, or enlightened. One sho=
uld
not be testing with high-context low-entropy sentences. One should be
using nonsense words, or other ways to remove such context effects.
Miller, Heise and Licten (1950's) did this by showing the subjects a list=
that contained
the word they were about to hear, and this allowed them to use real words=
,
yet remove the entropy problem.

When one uses high entropy words, then I really wonder if speech is redun=
dant.
My feeling is that it is not. This feeling is based on the 50 or so years=
of articulation
testing by fletcher and the gang. See my IEEE  review paper on this topic=
. (I also have
one in JASA.)

One problem with redundancy is that what do you do when the two redundant=
cues
give you different messages? In other words, they are telling you there i=
s a problem.
This allows one to detect that the SNR is poor, but it just creates confl=
ict. It doesn't
reduce the error rate.

Jont

--
Jont B. Allen
AT&T Labs-Research, Shannon Laboratory, E161
180 Park Ave., Florham Park NJ, 07932-0971
973/360-8545voice, x7111fax, http://www.research.att.com/~jba
```

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Electrical Engineering Dept., Columbia University