7.1 Side and Rear Channels swapped internally

[Manik Möllers]

Internally, Reaper seems to misinterpret the placements of the side and rear channels.

1. when panning on a track
When panning to the side or rear with ReaSurroundPan I noticed that all my channel analyzer plugins like Izotope Insight) interpret the rear as the side and vice versa. Basically channels 5+6 and 7+8 are swapped (see screenshot).

2. exporting 7.1 files
when exporting with channel configuration metadata turned on and than importing to Pro Tools, rear and side are also swapped, following the interpretation of izope insight.

This indicated that there is a internal misinterpretation in Reaper's channel handling.

[schwa]

In 7.1, ReaSurroundPan uses 5/6 for the side channels and 7/8 for the rear channels. If you need channels in a different order for delivery or interoperability with other applications, you can insert the Channel Mapper-Downmixer JSFX plugin wherever it makes sense, either immediately after ReaSurround, or on the master, etc.

[Manik Möllers]

Hey thanks for the quick answer and the workaround.

When using Reaper's standard 7.1 panner preset, which follows the typical channel order (L, C, R, LFE, Lss, Rss, Lsr, Rsr), I think it's reasonable to expect that the exported audio's metadata should match this same channel arrangement. Given that both the in-track audio in Reaper and the exported 7.1 audio are misinterpreted by external software in the same way, it points towards a more deep-rooted issue within Reaper itself, rather than a simple configuration mistake.

[schwa]

Originally Posted by Manik Möllers

Hey thanks for the quick answer and the workaround.

When using Reaper's standard 7.1 panner preset, which follows the typical channel order (L, C, R, LFE, Lss, Rss, Lsr, Rsr), I think it's reasonable to expect that the exported audio's metadata should match this same channel arrangement. Given that both the in-track audio in Reaper and the exported 7.1 audio are misinterpreted by external software in the same way, it points towards a more deep-rooted issue within Reaper itself, rather than a simple configuration mistake.

This is the channel order displayed in ReaSurroundPan, which I believe is what you are calling the 'typical channel order':



That is in fact the channel order within REAPER. I think your external applications are expecting L C R LFE Lsr Rsr Lss Rss.

For inline processing, like with third-party surround plugins, there's no metadata attached to the channels so you either need to use the channel mapper plugin, or find some equivalent input configuration on the third-party plugin.

For rendered files, you can set the WAVEXT channel configuration metadata, which I believe does match REAPER's internal channel order, but there's no guarantee that external software will respect the metadata. If you are aware of different metadata that we could include that might help (short of supporting an entire proprietary system like Atmos, which we might do eventually), please let us know.

[Manik Möllers]

typical channel order

By typical I just meant the SMPTE channel order.

For rendered files, you can set the WAVEXT channel configuration metadata, which I believe does match REAPER's internal channel order but there's no guarantee that external software will respect the metadata

1. When I exported an 8-channel WAV file from Reaper, both with and without the WAVEXT channel configuration metadata, and then imported these into Pro Tools, it was clear that Pro Tools does indeed utilize the metadata. The playback for the left, right, center, and LFE channels matched correctly (without metadata it didn't match). However, the side and rear channels were swapped again.

2. When examining a WAV file exported from Reaper with included metadata using MediaInfo, the channel order is displayed as L, R, C, LFE, LB, RB, LS, RS. This ordering doesn't match the internal channel order of Reaper, but interestingly is the same channel order that 7.1 plugins are expecting.


3. Within Reaper's metadata settings, the 7.1 channel order is shown as L, R, C, LFE, Ls, Rs, Lsd, Rsd. The terms Lsd and Rsd seem unconventional, but based on the 5.1 channel order, it's likely that Lsd and Rsd refer to the rear channels. This configuration aligns with Reaper's internal channel order but does not match the channel order that MediaInfo detects in the exported file.


4. when importing an exported 7.1 WAV from pro tools (with metadata) to reaper, sides and rears are played back swapped as well when using L R C LFE Lss Rss Lsr Rsr.

For inline processing, like with third-party surround plugins, there's no metadata attached to the channels.

In my tests with Pro Tools, the inline processing always follows the Film standard for channel ordering. In Reaper, all the 7.1 plugins I've checked (Fabfilter Pro-Q3 now as well) expect the side channels to be on 7+8 and the rear channels on 5+6.
Considering this setup is common across all my tested plugins, it would be really helpful if there were a more straightforward way to modify this inline channel order to align with these expectations.

In summary, Reaper exhibits multiple inconsistencies in channel ordering for 7.1 audio, both in its internal handling and when exporting files.

[schwa]

OK, yes, there is a problem here. Let's use Ls/Rs for the side speakers and Lb/Rb for the back speakers.

SMPTE 7.1 is L R C LFE Ls Rs Lb Rb. REAPER uses this order internally.

WAVEFORMATEXTENSIBLE and CoreAudioBaseTypes are metadata specifications created by microsoft and apple, which are identical up to a point. For a given set of speakers, this metadata can specify only one possible channel order. For 8 channels, the only channel order supported by these specifications is L R C LFE Lb Rb Ls Rs.

Unfortunately, the coreaudio specification calls this order L R C LFE Ls Rs Lsd Rsd, where Ls means "left surround" and Lsd means "Left surround direct". Ls/Rs actually means the rear speakers and Lsd/Rsd means the side speakers.

Regardless of the confusing/inconsistent speaker naming that exists in the world, the basic problem is that SMPTE 7.1 cannot be specified using this metadata. I think the least confusing way for REAPER to handle this inconsistency is for ReaSurround to rename the existing 7.1 format '7.1 SMPTE' and add another entry for 7.1 that matches the WAVEXT channel order.

This will ensure that existing projects are unaffected, including projects that have already dealt with this problem by swapping channels downstream of ReaSurroundPan, but provide a way for new instances of ReaSurroundPan to avoid having to swap channels when interoperating with a system that expects L R C LFE Lb Rb Ls Rs.

And if anyone is aware of a metadata standard that is reasonably well adopted that can specifify arbitrary channel orders please let us know!

[schwa]

[schwa]

The latest REAPER prerelease build adds handling for this. If you are able to test it out that would be very helpful. Info about prerelease testing is here: https://forum.cockos.com/forumdisplay.php?f=37

[Manik Möllers]

Hey sorry for the late reply and thank you very much for taking care of this so fast. That sounds good and should be able to fix most the problem. I tested it in the panner and now it is "correct" when changing the setting in the panner to "7.1 surround".

I try to find time to test this more in depth but right now I have a lot of projects and not enough time.

If I got everything right, this should be the way when using the new panner profile:
To get correct 7.1 metadata from reaper and also have correct playback for imported 7.1 files with metadata you would have to have the swapped SMPTE order from start to end.
So I would have to swap the channel order from input (reaSurroundPan) to my output (Actual Channel order of my monitor speakers) and than everything should work correctly.

[Manik Möllers]

Okay its working now. My setup is as follows:
Hardware outputs:
1 L
2 R
3 C
4 LFE
5 Lb
6 Rb
7 Ls
8 Rr

Reaper outputs Match Hardware Outputs (1=1 2=2...)


Using the new panner preset I can export it with correct metadata now (tested by importing to pt)

TLDR: It Works ♥

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Also some plugins (Like for example Stratus or ProQ) change their Output depending on the track channels. It would be awesome, if I were able to set odd channel counts to be able to use 7.0.

What I am missing most is to have mono tracks. This would make it much easier to accurately measure loudness and use mono plugins for that