calibration, need help

[Marso]

Can anyone help me wit this?
I've calibrated the 888/24 at -16db and the AD8000 too. Now what I get is a difference of 6 dbs of input between the two units! AD 8000 is 6 dbs lower. Also, if I'm increasing the signal, the signal gets louder with the 888 until it reaches 0db but does'nt get any higher than -6 on the track recorded with the ad 8000. Why the disparity?
Thanks.

[D Clementson]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Marso:
Can anyone help me wit this?
I've calibrated the 888/24 at -16db and the AD8000 too. Now what I get is a difference of 6 dbs of input between the two units! AD 8000 is 6 dbs lower. Also, if I'm increasing the signal, the signal gets louder with the 888 until it reaches 0db but does'nt get any higher than -6 on the track recorded with the ad 8000. Why the disparity?
Thanks.<HR></BLOCKQUOTE>

Could you precisely describe your calibration procedure, including the setup of any external gear, and details on all cable wiring? 6 dB error sounds suspiciously like a balanced/unbalanced issue but its impossible to know whithout more data.

DC

[Krusty]

exactly,

run a test tone out of all outputs on both AD8000 and 888/24.They "should" all match.
route those outputs to you inputs.. into new AUX tracks in PT

IF the levels of the inputs are off.. you are NOT calibrated.

[Marso]

Fellows, here is what I do...
I generate a tone that reads 0db on a Dorrough meter, I then patch it directly into every inputs of the 888 and ad8000 (one by one) and adjust the inputs to read -16db.
I then patch the outputs on the Dorrough meter (one by one...lenghty) and make sure they all read 0db analog. I cannot (if I'm not mistaken) adjust the outputs on a AD8000.
One thing I have'nt done yet is bypass my patch bay, it is a high quality patch bay and it would be very odd to have the exact same problem with 8 of the 24 inputs but I'll make sure anyway.
What am I missing??

[D Clementson]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Marso:
Fellows, here is what I do...
I generate a tone that reads 0db on a Dorrough meter, I then patch it directly into every inputs of the 888 and ad8000 (one by one) and adjust the inputs to read -16db.
I then patch the outputs on the Dorrough meter (one by one...lenghty) and make sure they all read 0db analog. I cannot (if I'm not mistaken) adjust the outputs on a AD8000.
One thing I have'nt done yet is bypass my patch bay, it is a high quality patch bay and it would be very odd to have the exact same problem with 8 of the 24 inputs but I'll make sure anyway.
What am I missing??<HR></BLOCKQUOTE>

Hi Marso:

Here's how I would do it: Generate a tone digitally from PT and route it to all of your interface outputs. Then, using the Dorrough, adjust the output levels of your interfaces so that they all match each other. The generator level and the Dorrough's calibration will determine your headroom. I would avoid the patchbay at this stage, as it is one more variable. Use a single cable instead so that you know the wiring is the same for all measurements. If the Apogee is not adjustable (although I think it has level trims inside the box), adjust the 888 so that it matches the fixed Apogee levels. Then, again using a single cable instead of the patchbay, patch each interface output to its corresponding input and adjust the input trims to give the same digital level in PT as the generator is generating.

Finally, once you're interfaces are all calibrated, verify that the patchbay is wired correctly by repeating the procedure using the patchbay instead of your single cable.

DC

[Marso]

I have verified (one more time) everything in my calibration procedure and consider that everything is A1. If I send a tone at -16 and record it on a dat thru aes ebu it will be -16. The problem is with pro Tools only.
I am sending in a tone at -16 and it reads and records -22.
This is a high end studio here and everything is wired with Mogami and the like. I've bypassed the patch bays to make sure and got the same results.
I also switched from one mix farm to another with no success. The ad8000 is calibrated to -16 and is outputting -16 (0 analog on a Dorrough meter and - 16 on a dat via aes ebu) when in INPUT status...BUT reads on the PT meters and therefore records -22, and plays it back at -22. It is always a difference of 6 dbs as soon as it is processed in pro tools. What can be wrong??
I just think that something is wrong with the ambus card.

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