line level voltage

[Bob Moose]

Good evening,

I would like to use some line level inputs of a Fireface 400 audio interface for non-audio data acquisition. This data (coming from sensors) can be scaled to any voltage range, but I don't know which maximum voltage such input can accept. Sorry if it's something obvious, but actually it's important not to damage the Fireface so I prefer asking before trying it in practice.

According to http://www.sengpielaudio.com/calculator-db-volt.htm, here it goes:

* if the inputs are in +4dBu mode (professional), the maximum input voltage should be about 3.47V (peak-to-peak)
* if the inputs are in -10dBV mode (consumer), the maximum input voltage should be about 0.89V (peak-to-peak)

Does it mean that when working in +4dBu mode, it's possible to send 3.47V (p2p) into a line level input without saturating it?

Regards,
-j

[dmills]

I don't know how that interface is calibrated, but you normally find +4dbu aligned to somewhere around -16dbFS, which would put full scale at +20dbu (which is more reasonable), so a nads over 15V peak to peak.

Note the subtle problem about RMS vs peak here, 0dbFS is a 'never exceed' peak value where +4dbu is probably as indicated on a more or less RMS reading instrument.

Regards, Dan.

[TheBazmeister]

I've done a similar thing before (not with that interface though) and didn't have any trouble with consumer level inputs up to about 10 V p-p from accelerometers and suchlike.