Native 24bit support

Moderator: flatmax

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moggyd
Posts: 22
Joined: Wed Jul 05, 2017 5:09 pm

Native 24bit support

Post by moggyd » Thu Nov 09, 2017 4:25 am

Hi,

I've been trying to use native 24bit and have hit a problem. If I run

arecord -f S24_LE -c 2 -r 48000 -D hw:0,0 | aplay -

All I get is noise. Above is fine with S16_LE and S32_LE.
Since arecord thinks that S24_LE is supported in hardware I would expect it to work.

uname -a reports:
Linux raspberrypi 4.9.60-v7+ #1048 SMP Fri Nov 3 16:05:21 GMT 2017 armv7l GNU/Linux

jessecobra
Posts: 14
Joined: Tue Oct 31, 2017 3:53 pm

Re: Native 24bit support

Post by jessecobra » Fri Nov 10, 2017 2:46 am

Does the codec support it? I forget which codec it is, check the data sheet...

My board arrives today or I would be more help ;)

moggyd
Posts: 22
Joined: Wed Jul 05, 2017 5:09 pm

Re: Native 24bit support

Post by moggyd » Fri Nov 10, 2017 4:22 am

According to this https://www.cirrus.com/products/wm8731/ yes.

"Stereo 24-bit multi-bit sigma delta ADCs and DACs are used
with oversampling digital interpolation and decimation filters.
Digital audio input word lengths from 16-32 bits and
sampling rates from 8kHz to 96kHz are supported."

moggyd
Posts: 22
Joined: Wed Jul 05, 2017 5:09 pm

Re: Native 24bit support [Resolved]

Post by moggyd » Tue Nov 14, 2017 1:02 am

This was caused by a custom .asoundrc file with a softvol. Once I removed it and reverted to a bog standard .asoundrc all is OK.
Bit weird since I was specifying hw:0,0 instead of the plug device. ALSA is a bit weird tho ;)

flatmax
Posts: 609
Joined: Sat Jul 23, 2016 11:39 pm

Re: Native 24bit support

Post by flatmax » Thu Nov 16, 2017 9:00 pm

I think if you try to change bit depth with sox after recording you will find that it did record ok ... just that your playback isn't recognising the 24, 3 byte format correctly ...

You can do something like :
sox infile -b 32 outfile
aplay outfile

and it should work - it is an interesting point that you would expect ALSA to be able to handle this ...

Matt
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