When attempting to use arecord to capture audio from a 24 bit source, and create a 24-bit .wav file I ran into the problem that the resulting file does not seem valid. Looking closer at the contents, it appears that arecord writes the 32-bit S24_LE samples verbatim to the file, and sets the number of bits per sample specifier to 24 in the .wav header, at the same time as it sets the 'block align' to 4 which I suppose is logical, although normally the block align corresponds to the frame size (in bytes) for the sample size specified in the bits per sample specifier.
A number of utilities and applications I tried refused to play the file back properly, including Audacity, VLC, sox and kwave, so I'm guessing the format written by arecord is not valid in this case. 24 bit audio as exported from Audacity for instance in reality corresponds to the ALSA S24_3LE format, i.e. the data is sent with no padding (resulting in a .wav 'block align' specifier of 3 for a mono stream).
Is this a known problem with arecord/aplay, or is it the other applications which have been less than accurate when implementing .wav file standard?
/Ricard