Speex dev - Oct 2007 - Implementation of a Speex based hardware VOCODER

Hi everyone,

     I?m a graduate student in a Brazilian Intitute of Technology, and I?m 
doing some academic research regarding secure voice transmission over phone
lines. One of our reserach goals is to implement a hardware vocoder, with low
bit rates, and a preferably free algorithm, to be used in this secure voice
system.
     Actually, there is a functional system using a proprietary AMBE board
(also a very expensive one) with a bit rate of 4800bps. When I found this
project, I tought the vocoder hardware could be implemented based on the Speex
code, since it works with similar bitrates.
     Is speex suitable for that? What are the main hindrances? I thought in
using some high speed uController (code would be implemented in C and ASM), or
a low cost FPGA (in wich the vocoder would be implemented in some hardware
description language, such as VHDL); what do you thing about this?
     Thanks in advance. Wishing to hear from you soon,

     Andr? Melo Carvalhais Dutra.

Hi,

Not sure what your actual question is, but Speex seems appropriate for
what you are trying to do. It can operate at many bit-rates, including
3.95 kbps and 5.95 kbps and it can be compiled to use fixed-point
instructions.

	Jean-Marc

Andre Melo Carvalhais Dutra a ?crit :
> Hi everyone,
> 
>      I?m a graduate student in a Brazilian Intitute of Technology, and I?m 
> doing some academic research regarding secure voice transmission over phone
> lines. One of our reserach goals is to implement a hardware vocoder, with
low
> bit rates, and a preferably free algorithm, to be used in this secure voice
> system.
>      Actually, there is a functional system using a proprietary AMBE board
> (also a very expensive one) with a bit rate of 4800bps. When I found this
> project, I tought the vocoder hardware could be implemented based on the
Speex
> code, since it works with similar bitrates.
>      Is speex suitable for that? What are the main hindrances? I thought in
> using some high speed uController (code would be implemented in C and ASM),
or
> a low cost FPGA (in wich the vocoder would be implemented in some hardware
> description language, such as VHDL); what do you thing about this?
>      Thanks in advance. Wishing to hear from you soon,
> 
>      Andr? Melo Carvalhais Dutra.
> _______________________________________________
> Speex-dev mailing list
> Speex-dev@xiph.org
> http://lists.xiph.org/mailman/listinfo/speex-dev
> 
>

It is not clear what you mean by "low bit rates".  If you are working
over
analog phone lines, then I would think that your speeds (including whatever 
overhead you add) should match available telephone modems in the V.32 or 
V.34 series, which would start at 4800.  Listen to Speex quality at 3.95 
kbps, and see if this is acceptable for you.  If it is, then Speex will 
offer great flexibility, while still reaching a bit rate below 4800.  Speex 
will also allow you to integrate the voice codec and telephone modem on a 
single processor.  Of course, you still need to find the telephone modem, 
and I am not aware of any free algorithms there.

If you want an even lower bit rate solution, then you can buy AMBE+ as an IC 
(search for AMBE-2000 or AMBE-2020).  I believe that these ICs are 
preprogrammed TI DSPs, and work in a range of 2000 to 4000 bps.  This is a 
closed solution, though, and more suited to a commercial product than to a 
research project.

I expect that converting Speex to an FPGA would be a tremendous amount of 
work, so a uController would be more practical.  There have been several 
messages lately about running Speex on the dsPIC processor.  If you want to 
run the encryption, voice codec, and telephone modem on a single IC, then 
you would need a more powerful processor.

Regards,

Jim Crichton

----- Original Message ----- 
From: "Andre Melo Carvalhais Dutra" <amcd@ita.br>
To: <speex-dev@xiph.org>
Sent: Friday, October 26, 2007 9:53 AM
Subject: [Speex-dev] Implementation of a Speex based hardware VOCODER

> Hi everyone,
>
>     I?m a graduate student in a Brazilian Intitute of Technology, and I?m
> doing some academic research regarding secure voice transmission over 
> phone
> lines. One of our reserach goals is to implement a hardware vocoder, with 
> low
> bit rates, and a preferably free algorithm, to be used in this secure 
> voice
> system.
>     Actually, there is a functional system using a proprietary AMBE board
> (also a very expensive one) with a bit rate of 4800bps. When I found this
> project, I tought the vocoder hardware could be implemented based on the 
> Speex
> code, since it works with similar bitrates.
>     Is speex suitable for that? What are the main hindrances? I thought in
> using some high speed uController (code would be implemented in C and 
> ASM), or
> a low cost FPGA (in wich the vocoder would be implemented in some hardware
> description language, such as VHDL); what do you thing about this?
>     Thanks in advance. Wishing to hear from you soon,
>
>     Andr? Melo Carvalhais Dutra.
> _______________________________________________
> Speex-dev mailing list
> Speex-dev@xiph.org
> http://lists.xiph.org/mailman/listinfo/speex-dev
>