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Newsgroups: sci.crypt
From: gtoal@gtoal.com (Graham Toal)
Subject: Re: Do we need the clipper for cheap security?
Date: Thu, 22 Apr 1993 10:54:34 +0000
Message-ID: <9304221054.AA01933@pizzabox.demon.co.uk>
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: There are chips which perform the voice compression/expansion.  They can't
: be expensive, because they exist in many phones connected to PBXs or on the
: PBX line cards, as well as in a lot of equipment which compresses
: voice-grade circuits to save the cost of long-distance, leased T1s or
: satellite circuits.

: I can't remember the generic term for these chips.  My impression is that
: this was a big deal 10 years ago, but circuits have gotten so cheap that
: it isn't done much now.

Codecs.  They have to get about 6:1 compression on 8 bit samples to squeeze
them down v32bis.  I played around with the lossless 'shorten' program
last night, but it only managed 2.5:1.  I've got some specimen CELP code
but it's not obvious that it runs in real time; I think it's just proof-of-
concept code, and I have some mucking about with file formats to do before
I can put my own sample through it.

Looks like the current option is to use a voice-mail modem with built-in
DSP chip to do this in hardware.  That means two modems for a system,
putting the cost at $600 upwards.  Ouch.  Maybe soon we'll be able to
do it in software on high-powered games consoles - isn't the 3DO an
Acorn RISC machine inside?  That cpu runs like shit off a shovel... and
will be nicely mass-market too.

G
