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Conformed original BWAVs are out of sync by up to a frame compared to the AAF


Matthias Richter
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posted by fellow sound mixer Frank Kruse on the avid forum (see the link for detailed information):

Hi,

I've finally found the time to trace an issue we've encountered for years now but that we always manually "fixed". Conformed original BWAVs are out of sync by up to a frame compared to the AAF.

Here's the normal workflow:

-Production sound recorded on Cantar, Deva, SD788 etc. Direct import into AVID MC converts to MXF audio.

-Copy all AVID audio media to PT and transfer cut via referenced AAF

-Expand to tracks using original BWAVs from production recorded.

So far so good. When listening to the conformed tracks against the AAF there are random sync inaccuracies from bang-on to light phasing to terrible echo.

I always wondered how this can happen when the files are identical incl. meta-data so there's no way a machine could mistake an in-point in samples after midnight for a different one.

So did some tests and it turns out that ALL the MXF media is not identical in length compared to the original BWAVs by random amounts between one frame minus 1 sample to one sample.

And the reason is that the AVID MC seems to fill any file that doesn't end on the full 24fps grid (or 25 if it's a PAL show) up to the next full frame.

On my current film the sound was recorded on a DEVA Fusion and this machine doesn't close it's files on full frame boundaries so there are all sorts of sync issues in the conform.

Bottom line is: The issue is a combination of Zaxcom not recording full frame length files and AVID manipulating the audio without notice.

I thing this should be addressed as it's causing labour intense hand-syncing on a clip-by-clip basis like in the days of tape -based conforms.

http://duc.avid.com/showthread.php?p=2094420

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Bottom line is: The issue is a combination of Zaxcom not recording full frame length files and AVID manipulating the audio without notice.

I thing this should be addressed as it's causing labour intense hand-syncing on a clip-by-clip basis like in the days of tape -based conforms.

http://duc.avid.com/showthread.php?p=2094420

So does the sync issues happen with Zaxcom BWFs only? If so, Zaxcom should address it, if not (i.e. the same on all the other machines you mentioned) then it seems to be a problem Avid need to fix.

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Frank just added:

 

Just checked BWAVs from an SD788 and they always start and end on 00-frames so it would be interesting to find out if a project based on SD788 files becomes out of sync as well.

If not that would pretty much confirm this as a PT bug or something you want to look out for on Deva-projects.

Frank.

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I remember many deva/fusion users asking for files that start and stop with a 00 frame timestamp to Howy on the old yahoo devalist.

 

The answer from Howy was this : I was able to do this in the ZFR and TRX but when I went to do it in the Deva the pre-record feature got in the way of being able to choose exactly when you go into record. I would have to totally rewrite the pre-record mechanism to implement that feature. -howy

 

So from what I understand it seemed Zaxcom left it like it was, because the risk of rewriting the code was probably too high and probably new bugs could appear. Ths sad thing is that they also left it that way for the Nomad.

 

 

Enviado desde mi Nexus 4 mediante Tapatalk

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another reply on the Avid-forum:

 

Hi Frank,

I saw this problem myself a good year ago on a TV drama. Main unit was deva and 2nd unit was SD. Main unit had sync issues and 2nd unit didn't.

When I spotted one of the deva location audio files to original TC I found that the WAV file didn't start on the frame edge. Plus the distance between start of the file and frame edge was the amount the conformed version of this WAV was out-of-sync with the AAF.

From what I am seeing the problem is that the deva doesn't start recording on a frame edge. MC doesn't understand sub-frames so it starts the file on the frame edge. Hence the MXF or media in the AAF is out-of-sync by the number of samples the WAV starts before the frame edge. I don't think it's a PT problem, but I may be wrong.

So from what I can see either the deva should start recording on frame edge or MC should truncate the start of WAV files so they do start on a frame edge on import, or both!

I followed this up with a recordist here in Sydney who uses SD recorders. The word back from SD was that they start all their recording on the frame edge for all their HD recorders. This adds up with what I saw on my drama show where the SD files conformed correctly.

Hope this helps.

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Interesting observations, I've come across these problem trying to develop a 'Conform' application.

 

It can be a pain how DAW's by their nature & audio files in general work to 'sample' (quantizing) intervals, NLE's to  frames (24th till 30th of a sec intervals).

Clearly SD have sussed (I use a 788T) that to be compatible to NLE's that at many levels are routed/stuck in the 1980's it's  a good idea to start a file at a zero frame, frame edge. IE hh mm ss & zero frame position.

 

Now Sony Vegas (which for reason I don't quite get, is not taken seriously) can have audio to it's natural sample accuracy in combination to video at it's 'frame intervals', Apple FCP can (sort of) too, Avid MC no-way. 

Why? How does Avid get away with this?

John L

(AATranslator, London) 

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I am guessing because no significant amount of people have raised it, or complained about it. Clearly, as publishers of Pro Tools, Avid could do this if they chose to or if there was enough fuss raised about it. It seems that even editors didn't quite understand why zaxcom files were not syncing properly until this test, so there has been probably little feedback on it. Now the question is does Avid expect audio manufacturers to fit around them, or will they change their code to accommodate more recording devices? Obviously it should be the latter, but all we can do is raise the profile of the problem in their forums and make them realise that it is a real problem which needs to be solved. 

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Everyone who is concerned about this should email Avid tech support and ask them to investigate this.

On the Zaxcom user forum Howy mentioned that he's getting in touch with avid to find out what's going on.

Couldn't hurt if they start receiving more complaints about this down their support channel though.

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Now the question is does Avid expect audio manufacturers to fit around them, or will they change their code to accommodate more recording devices? Obviously it should be the latter, but all we can do is raise the profile of the problem in their forums and make them realise that it is a real problem which needs to be solved. 

 

While I would like to get this resolved too, I'm not exactly sure how we can jump to the conclusion that "obviously" it's an Avid problem. Near as I can tell, Avid predates these digital recorders and given that Zaxcom is the only brand with issues, perhaps, in fact, it's Zaxcom's problem to fix. I'm just glad it seems there's a dialog going on between the two companies now.

 

Chris

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Well, I am basing that observation on the research provided in this thread and elsewhere, ie that Avid works in frames, even for audio, and thus 'fills in' audio to the frame edge, thus throwing it out of sync. When it could (and it is argued should) work to the sample level of DAWs like its own Pro Tools, and not alter the audio file to fit it into its old way of working. Of course, I don't care which side fixes it, and if Zaxcom fix it I will be happy. SD seemed to be clued up about this quirk, or legacy issue, whichever you want to call it. But it would seem to me sensible for Avid to progress to a modern way of placing audio in the timeline, since we don't know which other recorders may also suffer from this anomaly. Or are all recorders now and into the future have to be built to timestamp audio to conform to Avid's legacy issues? If it doesn't happen in other edit programmes, as John says, then it is an Avid issue as much as a Zaxcom issue. Whatever the outcome, I hope they both sort it out speedily. We don't need an argument about whose fault it is, we just need them to collaborate and sort it.

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  • 3 weeks later...

Boom Recorder does not start or stop at exact start or end of a frame. I will have to investigate if I can make Boom Recorder do this.

 

For your information the BWF standard does not specify that the recording needs to start and end at frame edges. In fact the timestamp in the header is sample accurate.

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We know that Sound Devices have accommodated this issue and Zaxcom have not, but what about other recorders that have timecode anyone know what they do?

Start / stop on any sample or on 00 of frames?

 

Sonosax,

Nagra,

Fostex,

Aeta,

Roland,

Tascam.

I have checked my Sonosax SXR4. I have imported some tracks into ProTools (Spot to original TC) As you can see in the enclosed picture. The recorded file doesn't start at frame bounderies. From the Avid forum: Nagra VI doesn't either. Best from Amsterdam, Alex

post-5151-0-42530300-1384510444_thumb.pn

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As someone mentioned in the DUC thread, if Avid is the one to fix this, it could turn into a problem for all of us, or for those who do post on smaller projcts, at least. Suddenly, Avid MC will have sample accurate audio editing capabilities, which is one if the reasons why audio often needs to be turned over to audio post.

OTOH I think in the fairly near future Avid will fuse MC and PT anyway

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As someone mentioned in the DUC thread, if Avid is the one to fix this, it could turn into a problem for all of us, or for those who do post on smaller projcts, at least. Suddenly, Avid MC will have sample accurate audio editing capabilities, which is one if the reasons why audio often needs to be turned over to audio post. OTOH I think in the fairly near future Avid will fuse MC and PT anyway
I disagree. The problem is Avid MC operates at a frame level and can't resolve at sub frames or samples. So when it gets a file that doesn't fall exactly on the frame boundry, it shifts it to compensate, therefore throwing the reconform out of sync. MC becoming sample accurate on the timeline i think would only positively affect audio post, and wouldn't give a video editor much that they can't do already. A little more accurate editing i suppose. Avid has stated this will be very complicated for them to fix, but I hope they do in future releases, as there is no good reason for an nle to shift media from where it is intended to be to keep sync. For now recorders can start on the frame edge as a workaround to avoid the problem, but that doesn't truely solve it.
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We know that Sound Devices have accommodated this issue and Zaxcom have not, but what about other recorders that have timecode anyone know what they do?

Start / stop on any sample or on 00 of frames?

 

Sonosax,

Nagra,

Fostex,

Aeta,

Roland,

Tascam.

Been meaning to search my test results for this info. A quick look suggests SD may well be way ahead of other file based location recorders in the T/c maximum  compatibility front.

SD have cleverly designed their recorders to have a file start point (in samples since midnight) at a 00 frame edge.

This has a number of advantages as the fcp rate becomes irrelevant, hh mm ss are common regardless of frame rate.

For most conversions from fps 'a' to 'b' there won't be an integer, (whole number)  number of frames equivalent. So an approximate 'rounded' number will have to be used.  

Many DAW's /NLE's don't read/know fps info anyway.

Or for example FCP which does read & log BWF fps info and when editing behaves as if edits /cuts are 'quantized' {snapped} to the bwf frame rate -- but NO, in fact the Project / sequence frame rate is used.

Also 29.97d & 23.976fps does not have an integer number of samples/frame - so a rounded approximation is the only option.

The fact is 'X' HH MM SS with no FF is  a very good idea to get round all the above issues.

It's often impossible to define a 'frame edge' in 'samples' -- 00 frames is a universally available exception.  

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It's often impossible to define a 'frame edge' in 'samples' -- 00 frames is a universally available exception.  

 

This is also implicitly assuming that midnight (TimeCode 00:00:00:00) is sample zero.  In Protools you can't import or spot a BWAV file more than about 12 hours past the beginning, so you set a start time for the project.   That then breaks the assumption of where sample zero is in terms of TimeCode.   What works for FCP doesn't work for ProTools.

 

Tom

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I believe the shift from 12 to 24 hours happened with Pro Tools 10.  Here's a blurb I found online about it:

 

"With Pro Tools 10, the timeline has increased from 12 hours to 24 hours, allowing any timecode stamped media to be placed at its Orig- inal TimeStamp location, regardless of the session start time. However, Avid DNxHD encoded QuickTime clips will not play back when placed anywhere on the Timeline past 20 hours. Please limit use of Avid DNxHD encoded QuickTime clips to the first 20 hours of the Pro Tools Timeline to avoid this issue."

 

Not an issue I've dealt with, so I can't offer actual end user feedback.

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Philosophical Opinion on Responsibility:

 

An NLE or any other software that does a conform or otherwise places or shifts things on a timeline needs to shift them according to the finest expected resolution of its content. If your software operates on the time relationship between picture and audio, that "finest resolution" is the sample. It is therefore the responsibility of the NLE to operate with sample accurate movements on a sample accurate timeline. (Not saying this is easy for Avid, just saying it's their responsibility).

 

While it may be a good, smart business move for a company like SD to compensate for another company's shirking of its responsibilities, it is certainly not the responsibility of recorder manufacturers to record on frame boundaries.

 

Or perhaps more succinctly, "You move it, you buy it". 

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