Paolo Saggese wrote: > Of course I plan to use the PC only to provide a "bitperfect" > (exact copy of the original media, normally CD) digital stream > to an external DAC. > > As you probably know better than me, the one major known problem > when you strive for the highest possible quality in digital audio > reproduction is jitter... and the best (if not only) way to really > minimize it is to use a good, clean and stable clock close to the > DAC chip, slaving everything else to that one. > > Thus, what I would need to do would be to "slave" the sound card > SPDIF output clock to the external DAC clock i.e. to make this one > become the "master clock" for the whole digital audio stream. An SPDIF input _always_ derives its clock from its signal. Besides, the clock for the actual DAC has to be a multiple of the bit clock anyway, so there must be a PLL to derive the DAC's clock from the input signual, i.e., the amount of DAC clock jitter depends more on the PLL implementation than on the input signal quality. > AFAIK, one possible way to do this is to set up a "fake" SPDIF > output from the external DAC and connect it to an input of the > sound card whose SPDIF output goes to the DAC for conversion. > > Of course the sound card must be able to "slave" (synchronize) > its SPDIF output clock with the one coming from its SPDIF input. There are sound cards that have a word clock input (M-Audio Delta and others based on the ICE1712 chip), but a word clock is only used to force multiple devices to run at the exactly same frequency, i.e., to prevent their clocks from drifting apart. This clock can _not_ be used as a bit clock for digital signals. Even if it were possible, the extra SPDIF connection would introduce additional jitter, thus the SPDIF signal received by the DAC would have more jitter, compared to the case where the sound card uses its own clock for the SPDIF signal. In other words, the sound card's internal clock is of higher quality than any clock that has to be received from an external device. > Thus, I would need a sound card which must be: > > * cabable of "bitperfect" (pass through) operation at CD standard > 16bit/44.1KHz (as well as, possibly, also at higher resolutions and > sample rates such as 16/48, 24/48, 24/96 and 24/192). Any cheap CMI8738-based card can do 16 or 24 bits at 44.1 or 48 kHz. Cards based on the CMI8768 chip (and some later 8738 models) or based on the ICE1712 chip support 24/96. Regards, Clemens ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
