On 3/28/16 9:30 AM, Georg Chini wrote: > 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. Understood, the point was whether you can remove this resampler to look for the root cause.
