Tri-Level Sync and Dolby E

[Chris Nuckols]

I'm trying to figure out a process that will allow me to record Dolby E to an HD format i.e. HD Cam SR deck and be able to punch into it later. I noticed in protools, that if I feed it hd reference and the dolby e 571 sd reference from the same tri-level sync and then record the dolby e stream into protools, the guard bands are not on the frame boundaries. Dolby said that you have to use there $4,000.00 tri-level sync converter the 579 to create something called "Dolby black burst". I'm curious if anyone else has run into this or how are you setting it up to record to an hd tape.

Does it only matter when you are doing 23.98? If you are doing 59.94 can you just feed the deck and protools 29.97 reference and everything be happy with getting the dolby e on tape, and then being able to punch in? We don't have a hdcam sr deck in house and we have to rent one when needed, so I can't run these specific test at the moment, so any advice would be greatly appreciated. Thanks for the help.

Chris

[splicestudios]

I'm not sure if this helps, but we recently installed Dolby E here and have been running that and our in-house HDCAM deck referenced to a black burst house generator, no HD or SD reference difference; we were rushing to get some stuff encoded and only needed to do one pass, no punch in.

Our next test will be to record the dolby E into ProTools and then use FCP to put it to tape - we have the decoder as a check to make sure things work correctly. I haven't see the waveform in PT, would be interested to know how you finally resolve it.

FYI, The video editor took a while to figure out how to get the HDCAM set up correctly for data on tracks 3&4 (no fade on punch ins, had to be cut edit, i.e. right on the frame, which is Dolby's recommended way of punching in for Dolby E). We're running everything in PAL, 25fps.

[PostMixinDude]

The way I understand it (and somebody correct me if I'm wrong) I mainly see Dolby E for broadcast applications only, which are usually 59.94 masters (29.97 NTSC)

Unless someone here has other insight as to why anyone would need to print Dolby E at 23.98?

[Chris Nuckols]

Thanks guys for the replies. i haven't needed to print at 23.98 yet but if A&E asks for dolby E anytime soon we might since they want there masters at 23.98 unless you can get a special agreement with them. As far as the broadcast only issue. We just laid dolby e to a digi beta so that the surround mix could be played back at one of the local theaters in Manhattan, so other venues are picking up the technology.

Splicestudios
you should do a punch in test in case you have to do a revision later. You can definitely record the dolby e into protools and export it. We deliver a lot of dolby e files that way. Is you show at 59.94 and your feeding the deck 29.97? That's what my concern is if the dolby e stream is aligned correctly at this point, if you feed everything 29.97 reference but your tape is at 59.94. If you did a punch and didn't hear a drop out then everything is ok. It should be but you never know till you actually try it. Thanks.

Chris

[Michael Klinger]

Here's some insight:

Dolby E has growing popularity for film festivals - that's one situation where 23.98 Dolby E will come up.

You definitely need Dolby's black-burst box for 23.98 Dolby E, but not for 29.97. There is also a 23.98 frame setting that you need to set in the encoder.

Going back to Pro Tools is no problem, just remember that Dolby E is 20 bit, so make sure that you are in 24 bit or it record as a noise. Dolby E used one pair of AES audio. If you play it as audio it will sound like white noise and the noise will play out at 0 full scale level and sometime will activate over and peak lights. This is not a problem.

The HDCAM SR's Dolby E audio track needs to be set up as a "non audio" track. This is a menu setting and there is a secondary data setting.

One of the "benefits' of Dolby E is that the data stream is controlled to work on chunks that sync to the frame rate, so, Dolby E is editable, and you can punch into it successfully. The cut option in the machine needs to be set for "cut" rather than cross-fade on punch in. This is the opposite of audio punch in which sounds cleaner with cross-faded punch in setting in the machine.

Remember that there is one frame delay on encode and one more on decode. There are different strategies for dealing with with the delay -- depending on the network or whatever the preference is on the receiving end. I think the best strategy is to slip the audio two frames early so that on decode it plays back in sync without any fussing but really it up to the receiving party.

It is really important to check your encode. There are a lot of tiny details and settings can go wrong. Ideally you should decode it with the companion decoder. At minimum, run it through an LM100 if you have one (which will identify the proper Dolby E signals as Dolby E), or any third party scope or decoder that will decode Dolby E.

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