As I'm continuing to tinker with 700D, I am at the point where I'm
running FreeDV on two full PC computers, with back-to-back audio
cables. This setup works flawlessly for 1600, but when I switch to
700D, I get occasional bursts of errors in the received data stream.
There's no band noise, because the setup is just two PCs connected
together. There shouldn't be much frequency offset other than the clock
differences between the sound cards. The sound cards I'm using are
solid, and I am actively using them with other DSP projects without any
issues. I can run 1600 for an hour or more without a single bit error
with the same hardware.
When I switch to 700D, the decoding runs okay for a while, then I'll get
a burst of a few bit errors, then a second later a few more, then a few
more, then it will go back to behaving. The audio becomes very
distorted, and the out-of-band text at the bottom is also corrupted
during the bursts, which are each sub-second in length.
The waterfall doesn't show any signal distortion when this happens. I
still have nice smooth rabbit trails up the screen, and a great SNR
(20-ish dB).
Has anybody else seen this with back-to-back testing of FreeDV and 700D?
The codec I'm testing against is the dev branch r3689, but it also
happens with the stock 0.8 library.
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