[alsa-devel] Question about Conversion to S24_LE from S24_3LE

[Takashi Iwai]

At Fri, 10 Aug 2012 08:44:12 +0000,
Fujikawa, Kazutoshi wrote:
> 
> Hello, Takashi.
> Thank you for your replay.
> 
> > > 0x00123456 (MSB 0(or 0xFF) padding)
> > 
> > This is the correct S24_LE representation.
> 
> I record a sound file by arecord command on Ubuntu.
> (% arecord -f S24_LE -r 48000 -c 2 ubuntu_rec_S24_LE_48000.wav )
> 
> Then this file was created, and it was LSB 0 padding.
> So I think that S24_LE format is LSB 0 padding.
> 
> % od -t x4 ubuntu_rec_S24_LE_48000.wav 
> 0000000 46464952 003a9824 45564157 20746d66
> 0000010 00000010 00020001 0000bb80 0005dc00
> 0000020 00180008 61746164 003a9800 ffffbf00
> 0000030 ffffc300 ffffc600 ffffca00 ffffd300
> 0000040 ffffd600 ffffdc00 ffffe000 ffffe000
> 0000050 ffffe400 ffffea00 ffffeb00 fffff800
> 0000060 fffffa00 00000400 00000500 00001000
> 0000070 00000f00 00001600 00001700 00001500
> 
> Do you know why this file is LSB 0 padding?

It depends on what format is used in the original PCM stream.
It'd make sense to have 00 in LSB if it was converted from 16 to
24bit.


Takashi