[LAD] [ot] rme fireface: weird balanced output measurements

[Fons Adriaensen]

On Sat, Feb 18, 2012 at 01:47:03PM +0100, Jörn Nettingsmeier wrote:

> fons, after i read your remark i asked around, and yes, the ff800 does  
> indeed use servo-driven outputs, so the voltage difference is  
> intentional and no cause for concern. i'll definitely investigate the  
> level differences between channels, but as you said, i'd better do that  
> with a sound card rather than a meter.

You could use a multimeter to _compare_  levels even if the actual
value is wrong. The important point with those servo-driven outputs
is that you should always measure between hot and cold, it's the only
voltage that is really defined by the line driver. The signal on each
of them separately w.r.t. to ground depends on how the other one is
loaded. It's done by a feedback circuit that tries to make the sum
of the two output currents zero.

If you have a good quality balanced line input with repeatable or
fixed gain (e.g. a multiface) just calibrate it once against a good
meter and then use jnoisemeter to measure RMS. The app also has
some standard filters and detectors for noise measurements.

Ciao,

-- 
FA

Vor uns liegt ein weites Tal, die Sonne scheint - ein Glitzerstrahl.