audio ringing/crosstalk

dennis · ‎2016-06-07

Posted on June 07, 2016 at 16:54

I posted on the eval forum but after further experiments trying here.

I'm using the STM32F746G Discovery. I'm using the audio_loopback.c demo slightly modified to use line inputs instead of mics. I get lots of crosstalk/echo/ringing when I set the audio gain at any usable level.

At first I thought maybe it was because of crosstalk between the input/output circuit board traces, but they are very short, and then I used an external low impedance buffer which should prevent crosstalk I would think.

I had to modify the BSP_AUDIO_IN_OUT_Init routine to allow an audio input type of INPUT_DEVICE_INPUT_LINE_1 and code below suggested that would be handled even though the example disallowed that as an input.

The slight delta is it uses CODEC_AUDIOFRAME_SLOT_02 instead of CODEC_AUDIOFRAME_SLOT_13. I don't have a conceptual understanding of what those slots mean.

It seems like what I'm trying to do should be fairly common: take an audio input from the line inputs and output it to the line/headphone outputs.

Pointers or suggestions?

Thanks.

#audio

mlrogers2002 · ‎2016-07-12

Posted on July 12, 2016 at 19:29

I am working on this now too, just started. Have you made any progress? Could you share the code you have so far?

mlrogers2002 · ‎2016-07-12

Posted on July 12, 2016 at 20:31

I found this example for stm32f769 disco, I think the right config can be gotten by digging around.

http://www.tjaekel.com/udante/files/STM32F769IDiscovery.zip

For the f746 disco, this example works, but lacks a line-in option. Probably the config can be figured out from the f769 example, and put into the f746 example.

http://www.tjaekel.com/DiscoveryF7Audio/index.html