On 05/28/2010 05:34 PM, [email protected] wrote: > On Fri, May 28, 2010 at 05:05:19PM +0200, Robin Gareus wrote: > >> Well, interpreting an 'experiment' that one has not conducted >> him/herself without knowing _all_ parameters of the setup is not >> something to encourage doing.. > >> Did you use symmetric (XLR) connections? > > Where possible, yes. Note that we are seeing a *modulation* > effect, the level of the spurious signals is proportional > to the wanted signal. It's not additive.
a 2nd measurement showing a measurement at - let's say 1215Hz would have made that clear in the first place. Anyway I take your word for it. Thanks for /organizing/ this little quiz; it's quite fun! >> Are the sample-rate settings of both cards identical? > > Shouldn't matter, as the connection is via an analog signal. > >> what was the physical distance between the devices >> (cross-talk)? > > It's absolutely not crosstalk. > >> Was there any ground-lift equipment (built-in?) in place >> or maybe you simply forgot to switch off phantom-power? > > All those would create additive effects, which is not what > we see. Phantom power, where available, was off. good; those charge-pumps that are used to create 48V from 5 or 12V often cause ripples in the supply voltage.. which in turn can influence the oscillator.. resulting in signal modulation. > Card X > has both line and mic inputs, all show the same result. > Mic inputs are driven via a balanced passive attenuator > with an output impedance of 50 ohm. > >> Anyway, good that you've labeled it 'quiz'; so here's my guess: >> >> You're encountering reflections (or even standing-waves) in the cable. >> (did you uncoil it? or was it a very short one?) >> Did you repeat the measurement? using different cables for example. > > No differnece seen between a cable of 3 m and on of 18 m. > > This will answer most other posters, except Chris: > >> Why 1015 Hz ? > > To clearly separate the signal from any 50 Hz harmonics. > > > One more hint: card X is a very high end one. It should > be 'perfect', or at least much better than card A. OT: I would not trust any consumer-grade audio-interface for signal differences larger than 80dB anyway. I'm amazed that card A shows such a low noise-floor in the loop-back test. > Ciao, > _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
