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? >> > 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
