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options for using arecord with USB streamer 2 years 3 months ago #41232

  • bourdess
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I've been trying to use a USBstreamer connected to a linux laptop to record 8 channel TDM. I'm using a generated test signal (square wave) and viewing the recorded .wav file post recording. While expecting a clean square wave, my recording show spikes and drops in the audio every time the square switches from high to low, or low to high. Additionally, all of the recorded sample values are positive whereas in the source material, the samples vary from plus to minus 1.

Due to the positive values of the samples, I figured this was a mis-interpretation of the sign bit. The only format acceptable for the hardware as far as arecord is concerned is 32 bit, signed, little endian. Tried using the signed 24 bit little endian format type, but arecord rejects that as not viable for this hardware.

Additionally, I hooked up an audio precision device to see if it was seeing the same thing. If I use options on the AP to indicate 24 bit data contained is 32 bit packets, I still see the same waveforms as was recorded by the USBstreamer with arecord. However, if I select the option on the audio precision to have the frame clock "shift left", I get a perfect, clean waveform coming out.

Does anyone have any advice on how to either use a different format with the USBstreamer and record, or how to get it to interpret things the way the audio precision tool does with the "shift left" option?

Thanks,

Mike

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options for using arecord with USB streamer 2 years 2 months ago #41403

  • devteam
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@Mike

We could be wrong but I think we talked on this already privately?
The USBStreamer TDM clocking might not be a match for your TDM slave device I'm afraid. We're not sure why they have the clock arranged such way as TDM8 is pretty common but maybe in the future we can see a way to solve that.

DevTeam
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options for using arecord with USB streamer 2 years 2 months ago #41435

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Yes, we did talk about this previously offline. Just to inform others on the forum, I will relay our solution:

The TDM format coming out of the Texas Instruments SRC4194 chip has a different behavior than what is expected by the USBstreamer for recording. We got around this by doing a board level modification at the ports of the TI chip where an inverter was placed in the signal path of the bit clock and 2 inverters (essentially a buffer to delay the signal to match bit clock) on the frame clock.

This modification seems to work, and I have been making clean 8 channel TDM recordings.
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