Steve Underwood wrote:
[whopping big snip]
The first bit of that's a tad patronising, isn't it,
You are the one who started out being offensive.
I'm sorry if you find disagreement offensive; you might not wish to read
beyond this
point if so.
and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.
I can't find too much about the old cards on the web now, but I found
http://www.amdevcomm.com/voice-mail-products/voice-mail-components/dialogic/dti_sc.html
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.
The same document, under the bit which you've quoted, says:
"(E-1) Digital trunks use separate transmit and receive paths to network.
Performance dependent on far end handset's match to local analog loop."
- i.e. the card does no echo cancellation.
Aculab didn't even offer echo cancellation on Prosody for years and,
when they did, it
consumed prodigious amounts of DSP. Nonetheless, the DTMF detection worked
perfectly well, even across 120 channels per 40MHz SHARC - there's just
no way
that those DSPs had enough horsepower to do echo cancellation across
that many
channels.
An Asterisk box with an el-cheapo quad E1 card in that I use for TDM-SIP
gatewaying
detects DTMF perfectly well with no echo cancellation.
You just don't need echo cancellation to achieve perfectly acceptable
DTMF detection.
ASR - yes, maybe, but surely only in the case where the application
requires barge-in;
even then, I'd be interested to see some test results, particuarly where
the outbound prompt
is killed the moment the ASR reports start of speech.
I'm afraid that your original bald claim - that "IVRs badly need echo
cancellation" is simply
wrong, misleading and irresponsible: those believing it will end up
spending large sums
of money on technology which they probably do not need.
--Dave
_______________________________________________
Freeswitch-users mailing list
[email protected]
http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
http://www.freeswitch.org
