[clug] broadband ISPs in Canberra
grail at goldweb.com.au
Tue Sep 28 04:14:04 GMT 2004
On 25 Sep 2004, at 14:24, Kim Holburn wrote:
> (in internet terms a phone call is a 2Kb connection).
Voice is much more than 2Kbps. People who squeeze it into 2kbps are
playing funny tricks like dynamic compression (range compression, using
the digital signal to encode frequency not amplitude) and acoustic
modelling (chopping out the bits that aren't needed for intelligible
speech). You can't, for example, send a fax over a VoIP line. Companies
like AAPT and Comindico are trying to get their VoIP services to
automatically detect voice vs fax calls, and engage the appropriate
(ie: none for fax) compressor for that call. But that's "coming soon"
to a telco near you, and not here yet.
If you've used Roger Wilco over dialup modem, you know what kind of
quality a 2kpbs voice link gives you - somewhat usable for PC gamer
communications (since you control the listening environment) but
useless for anyone else (do you really want to put on a set of closed
headphones every time you want to make a phone call?).
Of course, compounding the issue is the fact that various carriers -
both nationally and internationally - compress the heart and soul out
of the voice circuits in order to carry a few more calls (and thus make
more profit). This is why calling cards are so cheap - the service is
cheap too (then there's the whole minute-block billing or minimum call
"If knowledge can create problems, it is not through ignorance that we
can solve them." --Isaac Asimov
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