On Thu, 11 Feb 2010, Donald Tournier wrote:
Hi,
We have an application in our institute that will require recording of a digital signal via an optical cable. We have to be able to guarantee perfect bitwise reproduction of the signal (the odd bit error is not a problem). We're thinking of using SPDIF and ALSA to capture the signal (obviously we'll have to make sure the signal is properly encoded to begin with).
However, after some initial attempts, it's becoming clear that ALSA can't necessarily guarantee bitwise perfect capture. ALSA might change the format, or resample the signal after capture (although I've heard that can be turned off with "snd_pcm_hw_params_set_rate_resample (capture_handle, hw_params, 0)"). Also, the card that we've been playing with so far (SB Audigy2 ZS) apparently performs some low-pass digital filtering on the input stream anyway, and is therefore no use to us.
Getting raw S/PDIF stream for EMU chips is not so easy. They operates internally at 48kHz and everything is resampled to this frequency.
Jaroslav
----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.