" Is there some way to test the cards and measure their frequency? If so, you could do a pretty full-blown NTP for sound cards and that would be pretty freakin cool. "
- I have already suggested to measure average interrupt request frequency. If a card is playing N samples buffer with actual sampling frequency Fs, then time between interrupts per buffer empty is (N / Fs), i.e. for two cards it will be (N /Fs1), (N/Fs2) respectively. That is, average interrupt request frequency will be (Fs1/N), (Fs2/N) respectively. The device to measure the time can be the computer RTC (Real Time Clock) which is independent from both Fs1, Fs2. On Fri, 30 Dec 2005 23:47:41 -0500 [EMAIL PROTECTED] (Ross Vandegrift) wrote: > On Fri, Dec 30, 2005 at 05:42:32PM -0500, Lee Revell wrote: > > LDAS (the low delay audio streamer) does something similar - it has to > > compensate for the drift between two machines clocks' that exchange > > audio over the network but you could apply the algorithm to two cards on > > one box. It uses the ALSA API and is believed to accomplish this with > > the lowest achievable latency. > > The site sounds like it mostly attempts to compensate for network latency, > not clock drift between the hosts, though the PDF mentions some > "watermark algorithm" (google didn't turn up anything relevant to > timekeeping devices). > > Here's what I wonder for all software multi-card solutions: if the two > timing crystals are off by some small amount, you don't have any way > of measuring that, or knowing what the error is. Let's take an example: > > Two crystals are rated for 44100.0kHz. A's average frequency is > 44099.5kHz and B's is 44100.8kHz. As far as your software is > concerned, the cards are both running at precisely 44100.0kHz. As a > result, playing the same file on both cards results in card A taking > more time to play the same file - it is stretched. > > Is there some way to test the cards and measure their frequency? If > so, you could do a pretty full-blown NTP for sound cards and that > would be pretty freakin cool. > > -- > Ross Vandegrift > [EMAIL PROTECTED] > > "The good Christian should beware of mathematicians, and all those who > make empty prophecies. The danger already exists that the mathematicians > have made a covenant with the devil to darken the spirit and to confine > man in the bonds of Hell." > --St. Augustine, De Genesi ad Litteram, Book II, xviii, 37 > ------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Do you grep through log files for problems? Stop! Download the new AJAX search engine that makes searching your log files as easy as surfing the web. DOWNLOAD SPLUNK! http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click _______________________________________________ Alsa-user mailing list Alsa-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/alsa-user
