28 May
2010
28 May
'10
7:22 p.m.
On 05/28/2010 05:34 PM, fons(a)kokkinizita.net wrote:
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.
On Fri, May 28, 2010 at 05:05:19PM +0200, Robin Gareus
wrote:
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!
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. 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. 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.
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.
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. Ciao,