Re: problem with speech quality for tms320c54cst & msm7716 codec

Started by Jeff Brower August 29, 2006

> We are using TI DSP TMS320C54CST and CODEC from OKI(MSM7716) to
> build a simple pstn phone. We are having problem with audio quality
> when call on pstn line and playing audio to speaker using codec. We
> are using McBSP0 to communicate with CODEC and McBSP2 for DAA(line)
> interface.
> We have tested loopback and audio quality is fine. What we did in
> this test is sent audio packets received on line to line so
> basically we can hear whatever we speak. So audio packets from line
> are received fine and also send back fine. When same audio packets
> send on speaker, it adds lots of noise so we can hear whatever we
> say but with lots of noise. Same thing happen when we send audio
> packets from mic to line.

What happens if you download sine wave file to DSP memory, then run some code that
plays the .wav data directly to codec? You should use an precise waveform so you
know what to expect, and then look at what the codec outputs using a digital scope.
With a sine wave, if the codec messes up, you can see it more clearly.

My guess is McBSP0 is not initialized correctly for the OKI codec. Maybe polarity of
clock, framesync pulse width (N-bit delay), other setting. Did you ask OKI for
reference example for TI DSPs? Any McBSP code initialization they can give you would
be helpful.

> Please let me know if you can provide any consultancy help to help
> me fix this problem. If you can, please send me your contact info.

I don't think you need a consultant to fix this problem. You guys just have to debug