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Sending 64kbs(ADPCM) over a 8kbs line ?

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chewbecca

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pic adpcm

Hi ,
For a an application I need to send ADPCM (64kbs) data over a lossy copper link with maximum transfer rate of 10kbs. Any ideas as to how
to do it . I do not have DSP scale processing power so audio compression techniques(CELP,G.729 etc ) are out of question.
Any ideas as how to implement it , modulation?

--chewbeeca
 

shanren

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hi,what do mean of "10kbps"?if it is a digital line,compress the date is the only way.if no so,tell us the condition,maybe someone can help you.
REGARDS
shanren
 

chewbecca

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It is a analog line a highly lossy copper line over a distance of few kms.
By "10kbs" i meant was we were able to achieve a maximum data transer rate of "10kbs" using a modem (ftp) , this was donw purely for a test point of view in order to find the maximum bandwith the copper sustain.
 

xirix

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It's an aplication note from Micrchip about ADPCM compression with ordinary PIC, but only 1:2 ratio (from 64kbps to 32kbps)
 

wzdreamer

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I think that you can't use ADPCM 8kbps ... min 16kbps
according ITU-T G series standarts...
 

chewbecca

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I'am aware of it.
I wish to send 64kbs data only without any cmpression as I do not
have DSP scale processing power. Can I use modulation technique like
16 QAM and which can be implemented cheaply ( price factor) or do the members have some other ideas....
 

zoovy

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Sorry... No free lunch!

chewbecca said:
I'am aware of it.
I wish to send 64kbs data only without any cmpression as I do not
have DSP scale processing power. Can I use modulation technique like
16 QAM and which can be implemented cheaply ( price factor) or do the members have some other ideas....
chewbecca,
any digital modulation technique you will use, will use as much if not more processing power of some of the alogrithms of compression techniques.
If we dissect what you want to do into pieces we may be able to come up with something.

1) Analog signal comes in and digitized. (is the input analog?)The original signal is analog bandwidth limited to 0 to 8 kHz. You want to send the signal across an analog line to recover on the other side.
2) Do you want to do this digially of analog? If you want to do this digitally you need processing power. If you want this in analog domain a similar scenairo is necessary (additional circuit).
2a) possiblity of using analog? modulation techniques, AM, FM, PM, PAM...
2b) Doing it digitally? Do you have any delay requirements? Here is the chicken and egg problem. The more you can compress with an algorithm, the more memory you will need for that algorithm(storing and processing the number of samples).
3) Maybe you don't care how the solution is implemented but you just want the cost solution. In this case I would go and search for a single chip voice compression/decompression IC. Below is an example.

http://www.dvsinc.com/products.htm
or another solution from
http://www.voicepump.com
will do the trick.

4) Is the circuit full-duplex? Do you need to do the encoding and decoding simultaneously?

5) What is the sound quality you are looking for?

I don't want to sound that it is impossible and discourae you but this is a real tough project in trying to implement and encoder/decoder with just a PIC. Can you spare using ubicom(or scenix-old name. manufacturer of a very fasy pic clone) chip for the project? (sometimes I end up trying to solve the wrong problem!) Is there another variable in this project which you can change?

May be I am pessimistic today.
Good luck and please let us know of your findings.
 

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