192 I/O calibration question

[vudoo]

I'm a bit confused about the 192 I/O calibration. The manual says that the ouput is calibrated for -18dbFS ( output trim A ) and -20 dbFS ( out trim B ). Now i want to calibrate my interface, for film mix, at -20 dbFS = 0 and 79 db SPL at mix position ( my mix room is tiny 10x11 and the Dolby recommanded 85 db is way too loud ).
When i send a pink noise to my 192 I/O ouput and i switch the ouput trim from A to B....how come i don't hear any difference. I mean shouldn't there be 2 db of difference in level ( loudness ) ?? Thanks.

[jonnyclueless]

Originally Posted by vudoo

I'm a bit confused about the 192 I/O calibration. The manual says that the ouput is calibrated for -18dbFS ( output trim A ) and -20 dbFS ( out trim B ). Now i want to calibrate my interface, for film mix, at -20 dbFS = 0 and 79 db SPL at mix position ( my mix room is tiny 10x11 and the Dolby recommanded 85 db is way too loud ).
When i send a pink noise to my 192 I/O ouput and i switch the ouput trim from A to B....how come i don't hear any difference. I mean shouldn't there be 2 db of difference in level ( loudness ) ?? Thanks.

Is there any difference on the decible meter? Maybe the silence during switching trims is enough to cover up the 2dB difference.

[vudoo]

no there was no difference in the decibel meter reading...anyone ???

[jonnyclueless]

Originally Posted by vudoo

no there was no difference in the decibel meter reading...anyone ???

Then they are not cal'd differently.

Just set up a tone generator to the output at -18dBFS. It should show 1.228V on a meter using the A trim. For the B trim set the generator to -20dBFS and it should show 1.228V as well. I am willing to bet one of them doesn't.

I would never trust the factory calibration. So many thinks make the voltage deviate and I find myself calling my system almost every session. It may only be a channel here or there that goes out, but one can only imagine a trip fromthe factory to the store, then to your home.

[vudoo]

assuming they are calibrated proprerly, will i hear a difference in volume when i switch from trim A to trim B with the same tone ??? I'm a bit confused about calibrating interfaces input/ouput...is this a purely voltage matching or it affects level ( volume ) as well ??? Thanks