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Mark Raudonis
Data vs audio switch
on Dec 12, 2008 at 4:30:47 am

I know that you can switch the audio channels from "audio" to "data" for copying Dolby encoded programming. My question is... what does this physically do other than trigger the LCD to read "Data"?
Is there a limiter placed on the signal? I've noticed when we DON'T switch to data and still clone a dolby track it's all "over modulated".

Thanks for the info.

Mark





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Michael Klinger
Re: Data vs audio switch
on Dec 13, 2008 at 12:59:16 am

I can't offer a full technical explanation of what it is doing, or why a data option is needed on HDCAM but not other formats --- but simply stated the data setting tells the deck to record the signal as data rather than random white noise type signal it would be otherwise. Which (if you are curious), is what it sounds like if you listen to the track straight out without a dolby decoder in line.

If you don't have the data setting set to on when in record, the Dolby stream will never decode properly. Whether it is a the master or any later clone, The original and each successive record deck has to have those audio tracks set to data in the non audio menu. For Dolby E the sub setting is "burst." On playback the machine will know that it is data with or without the tracks set to non audio.

For formats that don't have a data setting (such as a Digibeta) the encoding works on any 20 bit or higher AES audio pair, including Final Cut and Pro Tools tracks. On devices that don't have a data setting the signal does look like is is peaking or" overmodulating" above 0 dBFS, but this is not a problem and can be ignored.

Mike Klinger
Tree Falls Post
(323) 851-0299
mike@tfpost.com
http://www.tfpost.com


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Bill Stephan
Re: Data vs audio switch
on Feb 20, 2009 at 9:31:05 pm

[Michael Klinger] "For formats that don't have a data setting (such as a Digibeta) the encoding works on any 20 bit or higher AES audio pair,"

Digital Beta does indeed need and have the same data settings. I'm not near a VTR right now, but I believe it's items 822 & 823 in the setup menu. The first is for recording, and the second is for playback (which can be set to and left on AUTO).

If you don't have these settings in your menu, your VTR's firmware needs to be updated.

The data settings bypass the digital filtering normally applied to audio.

Bill Stephan
Senior Editor/DVD Author
USA Studios
New York City


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Michael Klinger
Re: Data vs audio switch
on Feb 20, 2009 at 10:18:14 pm



Interesting information, Bill . . . As it turns out, neither of our Digibeta recorders have such menus.


I'll look into that and as it goes there is something new to learn everyday.

Oddly, We've never had a encode/decode issue as-is. but if there is a way to do it better, I'm all for it.

Mike Klinger
Tree Falls Post
(323) 851-0299
mike@tfpost.com
http://www.tfpost.com


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Richard Humphries
Re: Data vs audio switch
on Apr 15, 2009 at 9:03:43 pm

It's my understanding that when you choose DATA, it switches off some form of data correction intended to rectify errors in a digital audio signal. I could be wrong though.

-Richard


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