Re: [LAD] A little quiz about audio measurements...

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.

> 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.

> 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,

-- 
FA
O tu, che porte, correndo si ?
E guerra e morte !
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