Hi Matt,
I've managed to repeat the bug on my Rpi using SVN 3687.
Listened to the audio - strange noises at the 160ms frame rate. I've
traced it to the ofdm modulator, when I run this unit test:
./ofdm_mod /dev/zero ofdm_rpi.raw --ldpc --testframes 10
.... I can hear the noises in ofdm_rpi.raw
Will keep digging ....
- David
On 15/06/18 06:05, Matt Roberts wrote:
I have been tinkering with the 700D version of the codec, and I found an
interesting issue with respect to whether the machine producing the
modulation.
This applies to the codec, *without* the audio hardware. What I'm doing
is encoding audio files into encoded DV audio files on different
machines, then trying to decode them on another. This can be reproduced
using nothing more than the freedv_rx and freedv_tx utilities.
The sequence goes like this:
1. Start with a clean WAV file, recorded from a microphone.
2. Encoded the WAV file with freedv_tx ...
3. Decode the output of #2 file with freedv_rx ...
4. Play the result of #3 in Audacity, which also allows the waveform to
be seen.
I can do this just fine with the 1600 codec, using any combination of
Ubuntu Linux (U) and Raspbian.
With 700D, the U box can do the above sequence just fine. However,
that's as far as it goes. If I move the intermediate file between #2
and #3 from/to a RasPi device, the result is distorted audio at step #4.
The U box can't read RasPi encodings. The RasPi can't read encodings
from the U box. The RasPi can't even decode it's own encodings. But
the U box can handle its own encodings.
I have been able to reproduce this on old RasPi 1 machines, and on newer
3B machines. So it doesn't appear to be a hardware-revision-specific
problem.
If anybody is interested in more detail, I'll try to produce some more
data for you.
Still investigating...
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