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audio ringing/crosstalk

dennis
Associate II
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
2 REPLIES 2
mlrogers2002
Associate II
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
Associate II
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