by Glenn » Mon Apr 23, 2012 2:15 am
Hi Derek,
Most of my information is pieced together from different sources, and some of it is speculation. The 16 bit limit is mentioned on the ASIO page at Wikipedia, and repeated on the windows legacy audio page, also at Wikipedia.
The limitation is further hinted at in Audacity's bugs/known issues page. They don't call out MME/DS as the cause, but it uses these API to record. I came across a thread at the Vinyl Engine that discusses this very problem. The use of a hex editor to examine the files is explained, and that the files recorded at 24 bits in Audacity will have only zeros in the last 8 bits.
I used this knowledge to examine a file I recorded in WC when I was having problems connecting WC to the Juli@ s/pdif channels. Without a proper software connection, WC would record a blank file with the meter pegged somewhere just below -90 dB, even though it was set to record at 24 bits. I suspected this was a 16 bit channel as the SNR of a 24 bit file is around -140dB. I opened the recording in the hex editor, and found the first 16 bits were all zeros, with the last 8 containing what I believe is noise or dither of some kind. I'm assuming that if the recording was indeed through a 24 bit channel, that all 24 bits would contain zeros.
Does this make any sense?
The rest is subjective. Playback whilst editing in WC is noticeable poorer than what I heard through the line-out ports during the recording, which sounds like what could be truncation errors. It was the same when I was using the MAudio card, though at the time I was blaming the card.....I had no clue about any of this. Fortunately, it does not affect playback through an ASIO enabled player like cPlay or Foobar 2k.
Regards,
Glenn