Applying ADPCM g726

Hi,

I'm having a problem with my adpcm codec and I will appreciate any
advices/suggestions given.

I have downloaded my g726 adpcm codes onto a dsp(c5510) and I fed in
an analog signal(sound card output) into the processor. The output is
however disappointing as there were a lot of noise and static. 

The functionality of the adpcm codes is not in doubt as I had used the
ITU test vectors on the codes and the codes were able to encode and
decode correctly.

Can anyone with experience in this area advise me on how I can
actually improve the codes so that it will be more usable?

Thanks.

Regards,
Issac