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  #1  
Old 02-21-2002, 09:11 AM
Marso Marso is offline
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Default calibration, need help

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.
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  #2  
Old 02-22-2002, 12:29 AM
D Clementson D Clementson is offline
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Default Re: calibration, need help

<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
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  #3  
Old 02-22-2002, 09:30 AM
Krusty Krusty is offline
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Default Re: calibration, need help

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.
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  #4  
Old 02-24-2002, 10:01 AM
Marso Marso is offline
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Default Re: calibration, need help

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??
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  #5  
Old 02-24-2002, 02:43 PM
D Clementson D Clementson is offline
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Default Re: calibration, need help

<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
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  #6  
Old 03-01-2002, 12:17 PM
Marso Marso is offline
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Default Re: calibration, need help

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.

[img]images/icons/mad.gif[/img] [img]images/icons/mad.gif[/img] [img]images/icons/mad.gif[/img]
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  #7  
Old 03-02-2002, 01:36 AM
D Clementson D Clementson is offline
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Default Re: calibration, need help

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Marso:
[QB]
I just think that something is wrong with the ambus card.
[QB]<HR></BLOCKQUOTE>


This is possible. I've seen it before with the early AD8000's. ADC (only) data is skewed at the TDM bus in such a way as to shift the bits by one, yielding a -6dB gain change. The AD8000 isn't by chance the 2nd interface on a "Y" cable to a D-24 card, is it? I remember debugging that particular configuration for them, and the symptom was similar to what you describe. I seem to remember that they fixed it too. You may want to check with them to see if you've got the correct firmware, etc.

I can't say for sure that you're seeing a timing problem with the AD8000, but the 6 dB shift is suspicious.

Are the gains okay with the Digi interfaces?

DC
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  #8  
Old 03-03-2002, 03:42 AM
Marso Marso is offline
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Default Re: calibration, need help

Thanks for helping.
My set up is PTools mix core one mix farm and one dsp farm. Each interface is on its own card. I've swapped them to check...the same!
Yes it is an old firmware on the ad8000. I've contacted the store in order to get the upgrade but I'm still waiting for Apogee to send a new card and send mine back. I can't send it without having a replacement, I am in the middle of two projects and need the extra outputs.
And yes the digi 888 both work fine.
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  #9  
Old 03-03-2002, 11:51 AM
D Clementson D Clementson is offline
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Default Re: calibration, need help

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Marso:
Thanks for helping.
My set up is PTools mix core one mix farm and one dsp farm. Each interface is on its own card. I've swapped them to check...the same!
Yes it is an old firmware on the ad8000. I've contacted the store in order to get the upgrade but I'm still waiting for Apogee to send a new card and send mine back. I can't send it without having a replacement, I am in the middle of two projects and need the extra outputs.
And yes the digi 888 both work fine.
<HR></BLOCKQUOTE>


If the 888 works and the Apogee doesn't, my guess is that the problem lies in the Apogee firmware - especally if its an older model. Let us know if the new Apogee firmware fixes this problem.

DC
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  #10  
Old 03-04-2002, 07:32 PM
l anthony johnson l anthony johnson is offline
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Default Re: calibration, need help

[QUOTE]Originally posted by Marso:
[QB It is always a difference of 6 dbs as soon as it is processed in pro tools. What can be wrong??

It's probably something more complicated like already discussed, but just for the heck of it......

+6db is usually the exact level difference I get when I sum stereo to mono or -6 mono to stereo . You're not using stereo tracks/auxs to calibrate with pans centered are you? Or somehow splitting the incoming tone into stereo pairs? Have you tried just using mono tracks/auxes?
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