After several days of hard work I figured out what's wrong, and finally realized how this task should be solved properly. I generalized it in such way, that it could solve similar problems experienced by anyone who connecting multiple hardware clocked blocks in single graph (aka, "The two-clock problem", as named here: http://lists.gnu.org/archive/html/discuss-gnuradio/2010-05/msg00117.html). My solution introduces interface enhancement for sources and sinks and, as such, requires modification of existing blocks in GNU Radio source tree. So I would like to get feedback from maintainers before I start to prepare my contribution.
Basic idea is simple: 1. Source/sink estimates its current buffer level and buffer size each work() invocation and reports values outside via asynchronous message interface. 2. Special block inserted between source and sink receives messages from them, joins values in single pseudo-buffer, filters jitter and implements control loop: calculates deviation from 50% and corrects samples stream by adding duplicated samples or removing samples depending on deviation sign. Pros: - It works automatically and doesn't depend on clocks skew value, sample rate and other resampling blocks in graph. - It doesn't depend on (unknown) intermediate buffers underlying in OS or buffers between blocks, they affect only stream start-up performance, and this can be tuned via block configuration. For example, my virtual machine adds "invisible" ~250ms audio buffer/latency (actually it can be seen from large difference between ALSA buffer size value and value returned by snd_pcm_delay()). - Special block may be tuned (or implemented as different blocks) to adapt for various clock skew profiles, jitter profiles, etc. - Unlike timestamp-based solutions it robust and flexible enough to support various sources and sinks. Cons: - It distorts signal heavily at large skew between clocks. I wonder why nobody did it already. Please, comment on. -- View this message in context: http://gnuradio.4.n7.nabble.com/how-to-implement-auto-correction-of-sample-rate-in-flow-graph-tp45268p45337.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
