On Tue, 2011-06-14 at 10:37 -0400, Paul Davis wrote: > On Tue, Jun 14, 2011 at 10:03 AM, Ralf Mardorf > <ralf.mardorf@xxxxxxxxxxxxx> wrote: > > On Tue, 2011-06-14 at 08:22 -0400, Paul Davis wrote: > >> On Tue, Jun 14, 2011 at 8:11 AM, Ralf Mardorf > >> <ralf.mardorf@xxxxxxxxxxxxx> wrote: > >> > >> > And as you could read I found an issue. At Thomann (a German dealer) > >> > they claimed there are no sync issues, what I couldn't believe. Doing > >> > this test I found out, that there are bad phases. > >> > >> You DIDN'T SYNC ANYTHING. Or at least, your description doesn't > >> mention any kind of sync. > > > > That might be correct. The optical ADAT connection can't be used for > > sync? > > > >> And if you had tried to sync, you would have > >> found that you CANNOT sync two A/D converters unless they are the > >> exact same model (so that their pre-A/D buffer is the same size). > > > > I suspect the RME using other, better converters than the Behringer > > does. This is why I expect that a completely perfect sync for the phases > > might be impossible. Thomann (the dealer) claimed I'm mistaken ;), sync > > is possible. > > you're really deeply confused. let me try to illustrate (the diagram > is somewhat simplified to try to make the point more clear. the actual > reality is a bit more complex in terms of where the clock is actually > used, and so on). the section marked "buffer" refers, typically, to > some RAM into which a relatively large (say, 32 or more) samples can > be stored "in front of" the D/A converter. > > digital samples-> buffer-> D/A converter digital-side>internal > buffer->D/A converter analog side > ^ > | > | > sample clock > > the sample lock says "get another sample", so the device will fetch > another sample at precisely the same time (to within a picosecond or > so) of other devices using the same clock (if any). this is important. > > but ... the way each D/A converter circuit works is independent once > it has the next sample value available. the amount of buffering inside > the D/A converter is variable from converter to converter, as is the > actual conversion process itself. So lets put 2 of them together: > > digital samples-> buffer-> D/A converter digital-side>internal > buffer->D/A converter analog side > ^ > | > | > shared sample clock > | > | > v > digital samples-> buffer-> D/A converter digital-side>internal > buffer->D/A converter analog side > > it makes no different whether the sample clock is delivered from an > internal clock crystal, the ADAT cable, word clock via BNC or any > other method. once the samples are delivered to each D/A converter, > there is no "sync" anymore. > > this has nothing to with RME, and everything to do with the basics of > digital audio and digital-to-analog convertion. This was my understanding before I bought my RME and Behringer ADAT ;), than I was confused regarding to different claims :D, ok, you confirm my knowledge as correct, I had before I was confused :). So - the ADAT cable is enough for sync, but of cause - it can't perform magic to solve the issue you described Thank you, Ralf _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
