On 05/28/2010 08:07 PM, Ralf Mardorf wrote: > > > Ralf Mardorf wrote: >> Olivier Guilyardi wrote: >>> On 05/28/2010 07:36 PM, Ralf Mardorf wrote: >>> >>>> Folderol wrote: >>>> >>>>> On Fri, 28 May 2010 19:20:54 +0200 >>>>> Ralf Mardorf <[email protected]> wrote: >>>>> >>>>> >>>>> >>>>>> Veronica Merryfield wrote: >>>>>> >>>>>>> You can't trust a loop back test. >>>>>>> Any instability or dither on the reference clock of card A (fifo >>>>>>> clocking say) is not going to show in a loop back test. >>>>>>> Vrnc >>>>>>> >>>>>> Is Veronica Merryfield the winner? >>>>>> >>>>> I'm highly suspicious of the USB link, but can't quite put my finger >>>>> on why. >>>>> >>>> Card A is the USB card. For USB there could be several issues, but I >>>> don't have knowledge about buffering etc., but I guess it's card A and >>>> that there's a "instability" = jitter. I don't know what dither for >>>> CLK >>>> is. I guess the winner is Veronica Merryfield. >>>> >>> >>> I mentioned the clock problem first ;-) However, I thought it the >>> other way >>> around: I said that clocks being asynchronous that would generate >>> artefacts, but >>> Veronica seems to say that these are hidden when using a single clock. >>> >>> That's pretty much the same thing to me :p >>> >>> -- >>> Olivier >>> >> >> Did you also say for what card? A or X? If so, is Oliver the winner?
I said that the problem should be the same with the cards inverted, see below. >> >> Btw.: >> >> Ralf Mardorf wrote: >>> Gabriel Beddingfield wrote: >>>> On Fri, May 28, 2010 at 12:39 PM, Gabriel M. Beddingfield >>>> <[email protected]> wrote: >>>> >>>>> The 100 Hz (being 2x 50Hz, the power freq. in Italy) >>>>> suggests that it is probably related to some manner of >>>>> power supply. However, I have no theory why we're >>>>> getting 2x 50Hz (and I think I need one :-)). >>>>> >>>> >>>> Doh! When the AC wave is rectified, it results in a signal that is 2x >>>> the freq. because the negative part gets inverted. That's why we see >>>> 100 Hz instead of 50 Hz. >>>> >>>> -gabriel >>>> >>> >>> On card A or X? >>> Why AM and not additive signals? >> >> Is the jitter caused because of residual ripple? >> >> Summarized: >> >> Residual ripple for the DC could cause clock jitter and this for card A. > > And more: > > Clock jitter would cause AM (<-- not my knowledge, somebody else wrote > it) instead of analog hum, that would cause an additive signal. > > @ Oliver: Didn't you talk about syncing both cards? That's irrelevant. Here's what I said: "Well, it looks to me like this is caused by the fact that the audio cards clocks are not in sync. When you loopback card A with itself, both input and output are sampled with the same clock. But when you plug the output of card A into card X, you're dealing with two clocks which are not synchronized, and that result into these "artefacts". If I'm right then you should observe some /similar/ issues when repeating the experience with the cards inverted." Unfortunately, today my mails aren't posted on the lists, I don't know why. Some days it works, and the day after it doesn't. So look at the second post from Fons, there's my answer. What I said is about syncing yeah. Maybe that Veronica is being more precise mentioning clock instability or dither. But I'm very low in regard to theory anyway, I'm the intuitive guy ;-) -- Olivier _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
