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Channel Condition Issues

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Josh Petok
Channel Condition Issues
on Dec 23, 2008 at 4:12:29 pm

Here's the workflow:

- Black and code a tape on a SRW-5500
- Insert edit from Avid Symphony Nitris DX (3.0.5) 1080i 59.94, video & 2 channels of scratch audio all via HD-SDI
- send to mix house for layback

Here's where the problem comes up. When the mixer attempts to layback audio, he gets a solid red channel condition error. To rule out the tape stock, we black and coded the first 2 minutes of a fresh SR tape then output bars and tone. I was able to insert back into my own test tape several times with varying tracks enabled. When the test was sent back to the mix house, they got a condition error when inserting tone over the bars. We're assuming that the sync was part of the issue. We're using an AJA Gen10 for ext tri-sync. The engineer was originally using SD sync from the Gen10 which he said was fine for 59.94 outputs from the Avid. Just in case, we switched to HD ext sync out of the Gen10 and still had the same problem. I believe the audio engineer said they're using an Astro Systems sync generator.

After all of these tests, we decided to have the sound house output their 12 channel mix to a fresh piece of their black and coded stock. We planned to insert all the picture back to the tape. When we tried to insert, WE got a channel condition error. The tape plays back fine, but we can't insert into it.

My current course of action is capturing all the 12 channels to the Avid and inserting all of it back to tape together, which I really hope will work.

Any ideas or insight is greatly appreciated. I'm out of ideas.

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Dino Sanacory
Re: Channel Condition Issues
on Dec 30, 2008 at 3:46:01 pm

Chances are one of you has a deck that is out of alignment with regard to standard. By that I mean the mechanical alignment of the heads to the tape. That or you are both out just enough in opposite directions to each other. The result being that either of you can recover enough signal for playback but an edit from the other deck cannot be placed in the established tracks and results in the error you are seeing.

It could be bad sync at either end. The way to check that is to have the deck connected to absolutely nothing (video or sync), record a test pattern and tone on a tape from the internal generators. Then on the other deck, with again nothing connected, do an insert from the internal generators. If the channel condition is fine, it is probably a sync, wiring or connection issue at one end. If you still get the channel errors, it's time for a service to check head alignment.

Recording picture and sound all on one deck might generate a valid tape but it doesn't solve the underlying issue. These decks are incredibly complex machines that push the boundaries of what is possible in coupling mechanical and electronic systems. This used to be a common problem back in the days of D1 when even small changes in temperature or humidity could render a deck incompatible with itself.

Also, I would stick with tri-level sync. It is possible to use SD blackburst in some situations but it is less accurate.

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