Newsgroups: comp.speech
Path: lyra.csx.cam.ac.uk!doc.ic.ac.uk!daresbury!keele!uknet!EU.net!howland.reston.ans.net!usc!elroy.jpl.nasa.gov!ames!enews.sgi.com!wdl1!io!koontzd
From: koontzd@io.lrmsc.loral.com (David Koontz )
Subject: Re: CVSD speech encoders
Message-ID: <1994Aug9.163907.2157@wdl.loral.com>
Sender: news@wdl.loral.com
Organization: Loral Rolm Computer Systems
References: <jathomasCu8y02.JAn@netcom.com>
Date: Tue, 9 Aug 1994 16:39:07 GMT
Lines: 45

In article <jathomasCu8y02.JAn@netcom.com> jathomas@netcom.com (John A. Thomas) writes:
>We have an application that requires coding voice at 9.6k bps or less.  
>Ideally, we want to avoid the complexity of implementing CELP or 
>something similar on a DSP.  Barely telephone quality is fine. 
>
>CVSD techniques look attractive, especially in hardware.
>I have a data sheet for the Motorola MC34115, which seems as if it would 
>do the job.  I'm new to this area, so I would appreciate any suggestions 
>or comments.  Thanks in advance.
>

While 9600 baud CVSD is no where near telephone quality (unless you
are talking GTE), a few manufacturers have duplex CVSD chips with
integrated filters.

MX-COM, Inc. has a product MX609 which is a single chip full duplex CVSD
CODEC with on chip input and output filters, prgrammable sampling clocks
(derived from the filter clock) 3 or 4 bit companding algorithm.  

MX-COM also produces the MX619 (EUROCOM D1-IA8) and the MX629 
(Mil Std-188-113), typically used in digital military radios.

The MX609 is available in 16 pin SOIC, 22 pin ceramic or plastic DIP,
and 24 pin PLCC.

It is optimized for 16/32/64 kbps, to use at 9600 requires reducing the
filter input clock or using an externally supplied sampling clock or a 
combination of the two, to allow reduction of the top end of the pass band.

I would strongly recommend a VOGAD circuit to keep the input close to
the center of the CODECs dynamic range.

MX-COM also produces several chips of varying levels of integration intended
for voice storage and playpack, typically including a DRAM controller.

MX-COM, Inc.		   Mixed Signal Integrated Circuit Product Handbook
4800 Bethania Station Rd.
Winston-Salem, NC 27105-1201
(919) 744-5050
(800) 638-5577
(919) 744-5054 (FAX)




