On 28.03.2016 16:27, Pierre-Louis Bossart wrote: > On 3/20/16 2:24 PM, Georg Chini wrote: >> On 20.03.2016 19:13, Alexander E. Patrakov wrote: >>> 20.03.2016 22:41, Georg Chini пиÑ?еÑ?: >>>> Hello, >>>> >>>> I am still working on module-loopback and hit a problem that I cannot >>>> explain. >>>> When running a HDA card with long latency (333ms) I see that the >>>> resulting >>>> latency is not stable but varies around 300 usec. What is worse, the >>>> changes >>>> in latency are not even reported, module-loopback sees a completely >>>> stable >>>> value ( +/-10 usec). >>>> My setup: I have a bitscope dual channel USB oscilloscope attached to >>>> another >>>> machine. This device also has a function generator that I set to 1kHz >>>> rectangle. >>>> The signal is input to the HDA card and fed to the output of the same >>>> card via >>>> module-loopback. Input and output signal are measured using the >>>> oscilloscope. >>>> The movement of the edge of the output signal now shows the "latency >>>> jitter" >>>> which can be made visible by using the overlay mode of the >>>> oscilloscope. >>>> >>>> The result for HDA (module-loopback running with 500ms adjust time >>>> and 1s >>>> latency) is shown at http://georg.chini.tk/hda_333ms_3.png. Some of >>>> the >>>> original >>>> input signal is somehow fed into the output signal, don't know where >>>> this happens, >>>> so please ignore it as it has no impact on the result. >>> >>> No idea either, just some blind pokes... >>> >>> 1. Are you using the trivial resampler? Does anything change if you >>> change the resampler type? >>> 2. Do you get the same trace with a "weird" latency (not something >>> that can be derived from one second by multiplication or division by >>> small factors)? E.g. something like 318 ms. >>> >>> To me, it looks like something is sometimes creating an >>> off-by-one-sample error when copying the data. Which is exactly the >>> job of the trivial resampler, that's why the question. > > why is a resampler needed when doing a loopback on the same card? The resampler is there for the more general case when the two cards are different. I just have no system with two HDA cards, so I have to do my tests HDA -> HDA on the same card. > >>> >> Hi Alexander, >> >> no, I am working with speex-float-5. I just re-tested zitaj-bridge, and >> I was wrong, >> it shows the same behavior. I am also seeing double lines, so it is >> probably deeper >> down in the alsa driver. >> I also tested your 318 ms - same result. >> To rule out artifacts produced by the oscilloscope I fed the input >> signal directly to the >> second channel - this looks fine. >> The choice of the resampler does no longer have any impact on the >> performance >> of module-loopback. For small latencies (70ms - 100ms) I can keep the >> latency jitter >> now well below 100 usec for HDA -> USB on my system, this corresponds >> to a >> difference of 35 mm in hearing distance. When the USB device is run in >> batch mode >> the result is even better but less robust to changes in system load. >> zitaj-bridge is still somewhat better for HDA -> USB and USB -> HDA (~50 >> usec) >> but always fails after a few minutes complaining about excessive timing >> errors >> even for HDA -> HDA on the same card. >> >> >> >> _______________________________________________ >> pulseaudio-discuss mailing list >> pulseaudio-discuss at lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss > > _______________________________________________ > pulseaudio-discuss mailing list > pulseaudio-discuss at lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss
