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Steve Underwood wrote:
<blockquote cite="mid:49BFEBCB.9020708@coppice.org" type="cite">
<pre wrap="">[whopping big snip]
</pre>
<blockquote type="cite">
<pre wrap="">The first bit of that's a tad patronising, isn't it,
</pre>
</blockquote>
<pre wrap=""><!---->You are the one who started out being offensive.
</pre>
</blockquote>
I'm sorry if you find disagreement offensive; you might not wish to
read beyond this <br>
point if so.<br>
<blockquote cite="mid:49BFEBCB.9020708@coppice.org" type="cite">
<blockquote type="cite">
<pre wrap="">and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.
</pre>
</blockquote>
<pre wrap=""><!---->I can't find too much about the old cards on the web now, but I found
<a class="moz-txt-link-freetext" href="http://www.amdevcomm.com/voice-mail-products/voice-mail-components/dialogic/dti_sc.html">http://www.amdevcomm.com/voice-mail-products/voice-mail-components/dialogic/dti_sc.html</a>
which is pretty much a copy and paste from the old Dialogic web pages,
and you'll see it says "Cut through : Local echo cancellation permits
100% detection with a >4.5 dB return loss line". The Aculabs did the
same thing for sure. They just couldn't work without cancellation. There
were some very early Dialogic cards, using DTMF receiver chips and OKI
ADPCM chips, and had no general purpose DSPs. They performed really
badly because of the lack of cancellation, and were quickly replaced
with cards that put the OKI ADPCM, DTMF anf echo cancellation algorithms
into a Motorola 56k DSP chips.
</pre>
</blockquote>
The same document, under the bit which you've quoted, says:<br>
"(E-1) Digital trunks use separate transmit and receive paths to
network. <br>
Performance dependent on far end handset's match to local analog loop."<br>
- i.e. the card does no echo cancellation. <br>
<br>
Aculab didn't even offer echo cancellation on Prosody for years and,
when they did, it<br>
consumed prodigious amounts of DSP. Nonetheless, the DTMF detection
worked<br>
perfectly well, even across 120 channels per 40MHz SHARC - there's just
no way<br>
that those DSPs had enough horsepower to do echo cancellation across
that many<br>
channels.<br>
<br>
An Asterisk box with an el-cheapo quad E1 card in that I use for
TDM-SIP gatewaying<br>
detects DTMF perfectly well with no echo cancellation.<br>
<br>
You just don't need echo cancellation to achieve perfectly acceptable
DTMF detection.<br>
<br>
ASR - yes, maybe, but surely only in the case where the application
requires barge-in;<br>
even then, I'd be interested to see some test results, particuarly
where the outbound prompt<br>
is killed the moment the ASR reports start of speech.<br>
<br>
I'm afraid that your original bald claim - that "IVRs badly need echo
cancellation" is simply<br>
wrong, misleading and irresponsible: those believing it will end up
spending large sums <br>
of money on technology which they probably do not need.<br>
<br>
--Dave<br>
<br>
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