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Connecting Avid HD I/O to Dolby CP750 via AES/EBU
Old 22nd September 2012
  #1
Connecting Avid HD I/O to Dolby CP750 via AES/EBU

I tried to connect an Avid HD I/O to Dolby CP750 via AES/EBU a db25 connector.
I experience some clocking problem (clicks) and slow response time when hitting play on Pro Tools HD 10.3.
Has anyone successfully connected this way and has experience with it?

It also appears that cp750 has a different pinout db25 than an Avid i/o one.

Thanks.
Old 22nd September 2012
  #2
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minister's Avatar
 
🎧 15 years
Never hooked into a 750, but have a 650. Did you look in the manual for the pin config? Your cables need to match.
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Old 22nd September 2012 | Show parent
  #3
Quote:
Originally Posted by minister ➑️
Never hooked into a 750, but have a 650. Did you look in the manual for the pin config? Your cables need to match.
Thanks Tom, I am aware of the difference in pinout configuration.
Did your cp650 run smooth when connected digitally?
Old 22nd September 2012
  #4
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minister's Avatar
 
🎧 15 years
I did it analogue. So I am not much more help...other than, it sounds like a clocking issue. Not sure what the setting on the 750 would be.
Old 22nd September 2012
  #5
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🎧 10 years
I bet it's the combo that's causing it.
At least the 650 is sensitive to clocking on its inputs. Reclocking is often a no no, mostly requires a reboot.
And ProTools is awful sending crap out the HD I/O until the session is loaded.
Try putting something else in between, or try something but PT+HD I/O hardware to make sure it's not the CP unit in itself.
IIRC the CP doesn't like pulled clock either so make sure you test it @ pure 48kHz. We run our monitoring at true 48 from a SSL Alpha link and it works fine unless switching sample rates.
Old 22nd September 2012 | Show parent
  #6
Quote:
Originally Posted by ErikG ➑️
I bet it's the combo that's causing it.
At least the 650 is sensitive to clocking on its inputs. Reclocking is often a no no, mostly requires a reboot.
And ProTools is awful sending crap out the HD I/O until the session is loaded.
Try putting something else in between, or try something but PT+HD I/O hardware to make sure it's not the CP unit in itself.
IIRC the CP doesn't like pulled clock either so make sure you test it @ pure 48kHz. We run our monitoring at true 48 from a SSL Alpha link and it works fine unless switching sample rates.
Thanks Erik. It looks like cp is not intended for swift and frequent clocking changes.
I tried rebooting them both and I ran a real session at pure 48 KHz 24 bit.
Thanks to you advise, I am considering now to connect to CP750 through the Analog db25 connector.
Interesting how cp treats the signal and if there is any degradation.
...Thus a question which DA is better HD I/O or CP750 one.
Old 22nd September 2012
  #7
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Branko's Avatar
 
🎧 15 years
I have a 650 connected through AES to my 192 i/o.
Never had a problem with it, since the day one.
I even did some sessions at 44.1K and never had any issues with clocking.
The only Dolby equipment that gives me headache is the MME, as I couldn't connect it following the usual channel order (LCRLsRsLF), but had to shuffle the order, as MME was not receiving the sync. I'll check the exact order on Monday and post it, if that helps.
Old 22nd September 2012
  #8
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Branko's Avatar
 
🎧 15 years
OTOH, I'd always put my bet on Avid's D/A converters, instead of Dolby's.
Old 22nd September 2012
  #9
Thanks Branko for both replies.
Is Dolby acting only as a volume monitor controler when connecting via analog input? I mean what happens to a signal from analog in to analog out? I asume that nothing wrong. Also why are you connecting via AES if digi / avid DA's are better?
Old 22nd September 2012
  #10
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Branko's Avatar
 
🎧 15 years
I have the CP 650 connected as an insert in my monitor chain, so the final conversion before the signal goes to speakers is 192.
CP650 is a digital processor, so if you connect it via analog, it is going to convert to digital first. The version of 650 I have simply doesn't have any converters, so I use 192's converters for that task.
In a Dolby approved mixing studio, you have to have a CP, because you need to be able to play 35mm prints, and the CP provides DD decoding and analog pre-amplification, SR decoding, and 2>4 decoding. Everything else CP does, like speaker levels and EQ, can be achieved easier with other equipment.
If your stage is not going for Dolby approval, I'd skip the CP.
Old 20th October 2012 | Show parent
  #11
Just a little update for those it can be interested.
I soldered a special cable, which has a CP750 custom wired DB25 (CP unit has totally different wiring scheme from standard AES/EBU one) and the other end has a standard AKA Avid/Digi AES/EBU connector.
Marked it as well for future reference: CP and Digi.
Works wonderful with my Avid HD I/O now.
No idle time or whatsoever. Really cool.
Our Dolby unit has a special LRCLfeLsRs config (for some other tasks), so the only thing I had to change was the I/O layout in PT.
I am happy now.
Old 20th October 2012
  #12
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Branko's Avatar
 
🎧 15 years
Good news!
Now fill your agenda with bookings!
Good luck.
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