Thanks Clemens, that very helpful. We'll try to source one of these C-Media cards as soon as possible. Also nice to know about the "hw:x" trick, although I'm not too sure how to use that in practice. I've just tried this command, with no success: $ arecord -D hw:x -t raw output.raw ALSA lib pcm_hw.c:1435:(_snd_pcm_hw_open) Invalid value for card arecord: main:608: audio open error: No such device How exactly should this be used? Thanks, Donald. On 11 February 2010 18:26, Clemens Ladisch <clemens@xxxxxxxxxx> wrote: > Donald Tournier wrote: >> 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)"). > > If you open the device as "hw:x", ALSA will not do any conversions and > will give you the data exactly as it comes from the sound card. > >> can this be done? If so, which card/driver would be recommended? > > PCI(-E) cards based on C-Media chips (CMI87x8, CMI8770, AV200) are known > to allow bit-perfect digital capture. > >> Ideally, we would like to capture the raw SPDIF subframes. > > Some very old revisions of the CMI8738 did this, because proper decoding > of subframes wasn't implemented, but these aren't sold anymore. > > > HTH > Clemens > -- Jacques-Donald Tournier (PhD) Brain Research Institute, Melbourne, Australia Tel: +61 (0)3 9496 4078 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
