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 just read through the calibration thread and i want to calibrate my interface at -20 dbFS = 0 and 79 db SPL at mix position ( my mix room is tiny 10x11 and the 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.

[minister]

i found that the calibration for my 192 was WAY out of wack. so i used a multi-meter, connected the D-SUB to the analogue outs, selected the B trims, set a 1kHz tone for -20 (going out MONO channels), and adjusted the trims until each one read 1.228V (-20dBFS = 0 VU or +4 dBU, or 1.228v). then, i would go to the trouble of calibrating the A trims as well. THEN you will hear the difference.

you need a mult meter with enough resolution to read 1.228.

hope that helps.

[Frank Kruse]

Based on this quote from the 192 manual:
------------
The 192 I/O is factory-calibrated so that its
+4 dBu input operating level is set for 18 dB
headroom above +4 dBu (maximum input/output
+22 dBu).
------------

I was going to ask how do you guys calibrate -20dBFs to 0VU=+4dBU since the 192 only goes up to +22dBu absolute level. When calibrating -20dBFs at +4dBu you would always clip the 192 2dBs before full-scale is reached

frank.

[vudoo]

Well theoretically you're right but practically speaking i don't think it's as simple because most analog devices ( Betacam Deck, 2"multitrack..) craps out at roughly 12 db above 0. Therefore if you know you will end up on Beta SP and if you were calibrated at - 20dbFS, your mix should not hit above - 8 dbFS ( 12 db headroom ) wich is still way below the absolute distortion point of the 192I/O.

[Frank Kruse]

I´m talking about mixing for film. the dolby-mod has 20dB of headroom above dobly-level.

A device made for playback on a film-stage shouldn´t distort 20dbs above 0VU=4dBu, if you ask me...

If I´d mix for BetaSP day-in-day-out I wouldn´t calibrate to -20dBFs anyway.

frank.

[Rail Jon Rogut]

Most analog consoles will clip at +18dBu.. with older Neves clipping at about +22dBu.

The 192 manual states that the 192 will clip at +26 dBu (page 21) -- which gives you 2dB of headroom when calibrated at -20dBfs = +4dBu. At -18dBfs, you have 4dB of headroom. The maximum output of 22dBu simply means at full scale you'll be outputting +22dBu (your maximum value).

The full quote:

In +4 dBu operating mode, the 192 I/O is a 24-bit digital audio device capable of producing audio signals up to + 26 dBu across +4 dBu input/output. The default headroom value is 18 dB. This translates to a maximum output of +22 dBu.

Rail

[vudoo]

Frank,

Well, unfortunately i don't have the luxury of mixing for different media...usually the film mix will end up on DVD, Beta SP, Beta Digi.....Besides i think Rail got the right answer,the absolute level is + 26 dbFS and not + 22 dbFS so wether you're calibrated at 18 or 20, you're cool.

[Frank Kruse]

Thanks Rail,

so I misunderstood the manual. It sounded like the maximum absolute level of the 192 is +22dBu.

Frank.