Pro Tools 5.1 audio track channel order

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Pro Tools supports a variety of surround sound formats, but of course the most common is still 5.1 surround.  This breaks down into the standard channels of Left, Center, Right, Left Surround, Right Surround, and LFE.  There are several different standards for how we can order those 6 channels.  Let’s take a quick look at how we deal with this in Pro Tools.

Under the Setup Menu, on the “I/O…” setup page, you’ll see an option for default 5.1 path order.  This lists the common standards for how to arrange the 6 channels of a 5.1 path.

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You can see in parentheses the descriptions of the different channel orders.  There is often some confusion regarding the way channels map on a 5.1 audio track in Pro Tools.  This is due to the fact that there are these different standards in the first place.  Life sure would be easier if there were only one channel order!

These are also just the four preset default options.  It gets even messier because Pro Tools lets you route the channels of your 5.1 path to any physical output you want!  You could even set up a goofy output like this if you wanted to:

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However, the most likely output option you’ll use is the SMPTE standard, like this:

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What’s the main benefit of the SMPTE standard over any other?  The main advantage is that L and R map to outputs 1 and 2, just like a stereo setup.  So when switching between 5.1 and stereo, the physical outputs for L and R don’t change.  It’s simply a matter of convenience.

So this is all fine and good, but it brings up a very important question: if I can set the output path of my 5.1 audio track to any old random output that I like, how does Pro Tools know which channel goes where?  The I/O page identifies the channels as L, R, C, LFE, LS, and RS, but how does Pro Tools know which channel of audio on my track is actually the center channel, or the left, or LFE?

It knows because within the audio track itself, there is a fixed channel order that is used and never changes; the “film” standard.  Regardless of what kind of crazy output you have your 5.1 audio track going to, the audio on the track itself must be ordered this way: L, C, R, Ls, Rs, LFE.  Take a look at this 5.1 audio track, and you can tell just by looking at the modulation that this is in fact the order of the audio channels, from top to bottom.

Screen Shot 2014-03-18 at 6.07.14 PM

 

You can see what looks like music modulation on the first and third channels, so this is likely L and R.  The second channel shows unique and large modulation not shared anywhere else, and it sure looks like dialog.  So this must be C.  The fourth and fifth channels look like a very low-level version of the modulation on the first and third channels, so these must be the surrounds.  Lastly, the sixth channel has some unique modulation that is sparse, so this is probably the LFE.

Pro Tools has to have an absolute somewhere, in order for the I/O page to make sense and function.  So this is that absolute.  The audio channels on the track itself must be in film order.  From this one consistent starting-point, you can then route things anywhere you like!  Just remember, the audio channels on the 5.1 track itself are in film order from top to bottom: L, C, R, Ls, Rs, LFE.  So even though you are probably going to use the SMPTE order for the main output to your speakers, the audio on the track itself it always in film order.

 

2 Comments

  1. Hey Alexey,
    Just wanted to drop a line and thank you for a great blog with excellent content. Right to the point, easy to follow and genuinely helpfully.

    Please keep up the good work man!

    Gene

  2. For quite a number of years, since Pro Tools has had the ability to both read and create multichannel sound files, this explanation was correct. But as I've just learned yesterday, just when you think you know how to use Pro Tools proficiently nothing is preventing Avid changing the rules without letting everyone know. Please see my post I left at the Avid forum about this very topic.The short version is that files read from disk or written to disk are not always in the Film order format as expected. Pro Tools version 9 added the ability to read Extensible Broadcast WAV files that are rigidly defined to be SMPTE ordered. But the session will display it top-down in the Film order. Pro Tools knows if a file is Extensible or not by the presence of something called a channel-mask. This is found in the header of all Extensible Broadcast WAV files.Outputting multichannel files were still Film ordered at that point. When version 10 was released, Avid changed the rules for writing files. Now, 5.1 files are always written as Extensible Broadcast WAV files. I just learned this and it was a rather rude awakening for me since my entire workflow has always been to work around the previous constraint.For years, I've complained to Digidesign, and later Avid, about the lack of being able to choose a channel order for interleaved files. This kind of user control would be very simple to implement. This problem becomes so much worse when things remain locked down and the rules subject to change on a whim.

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