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Topic: Why are the "back" surround channels labelled "R"? (Read 3424 times) previous topic - next topic
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Why are the "back" surround channels labelled "R"?

I wish foobar2000's output meters would stick to the standard wave file labelling for surround channels where appropriate, instead of substituting "R" for "back". I'm not sure I understand the logic behind it, and I'm easily confused.... :)

I assume "R" was originally used to distinguish "surround" from "side" when "S" could be either, and that's somewhat logical, although it's still different to the way the rest of the world does it where "S" is surround unless there's back speakers in which case "S" means side. Foobar2000 is differing from the way it's generally done, and I'm easily confused..... :)

Re: Why are the "back" surround channels labelled "R"?

Reply #1 –
''R'' means ''rear''. Yes, using ''rear'' instead of back can be slightly fonfusing, beacause official names of back speakers are ''Back left'' and ''Back right''.
But using ''S'' for ''side'' seems logical, beacause official names for side speakes are ''Side left'' and ''Side right'' according to https://en.wikipedia.org/wiki/Surround_sound#Standard_speaker_channels

Re: Why are the "back" surround channels labelled "R"?

Reply #2 –
Yeah.... no arguments about using "S" for "side".

It also makes sense because in a perfect world (the way I understand it) the "S" or "surround" speakers in a 5.1ch setup are supposed to be placed each side of the listener, or just a little back from there, but there are no "back" speakers as such.
When a second pair are added for 7.1ch, the extra speakers are placed behind the listener. The "S" speakers are still the "S" speakers, whether they be surround or side.

The way foobar2000 labels them, the "R" speakers move from the "side" in a 5.1ch setup to the "back" in a 7.1ch setup.

I don't necessarily think labelling the surround speakers in a 5.1ch configuration "R" is a bad idea, as it distinguishes "surround" speakers from channels specifically labelled as "side", but other than that I think the back channels should be "B".

It's probably mostly Microsoft's fault for deciding on a wave file channel order that's out of order.... at least for a home theatre surround set up. I guess when the wave file channel order was decided on it was based more on a movie theatre surround setup, hence the back speakers coming before the side speakers and in between those there's front surround speakers that probably don't apply to any standard home theatre setup. Maybe we'll have to wait for wav format extensible version 2.0. ;)

Re: Why are the "back" surround channels labelled "R"?

Reply #3 –
Actually it depends on the codec and channel layout.  Any DTS CD will actually show Surround Left and Right (SL / SR).  Some DSPs such as Pro Optimizer's Downmix AC3/DTS component won't work in the DTS case without re-ordering the channels to be rear channels instead of side channels without using something like Matrix Mixer or converting the file using Matrix Mixer as a DSP.

I do know that there's plugins that can let your re-order the channels if necessary and you can even re-encode some files with the desired channel order with a digital audio editor or foobar2000's converter.  Explore a bit, rather than complain about it.  Chances are you might find something that works for you.

Re: Why are the "back" surround channels labelled "R"?

Reply #4 –
Quote from: Chibisteven on
Actually it depends on the codec and channel layout.  Any DTS CD will actually show Surround Left and Right (SL / SR).  Some DSPs such as Pro Optimizer's Downmix AC3/DTS component won't work in the DTS case without re-ordering the channels to be rear channels instead of side channels without using something like Matrix Mixer or converting the file using Matrix Mixer as a DSP.
I do know that there's plugins that can let your re-order the channels if necessary and you can even re-encode some files with the desired channel order with a digital audio editor or foobar2000's converter.  Explore a bit, rather than complain about it.  Chances are you might find something that works for you.

First of all, re "rather than complain about it"... well I was going to say "bite me", but maybe I didn't explain my thought process adequately. In a nutshell, if the 'back" channels are being used for surround I think foobar2000 should call them "back" instead of "rear". My suggestion was really no more complicated than that, although I think foobar2000 probably should stop using "back" for 5.1ch surround anyway. To expand....

I know the standard 5.1ch codecs (AC3 or DTS) have "surround" left and right channels, but there's no such channel assignments on a PC, so they have to be decoded as either "side" or "back" channels. As a result, for 5.1ch audio, most lossy codecs accept either the "side" or "back" channels as the surround channels for input when encoding, but it's quite possible to feed the encoder "back" channels for "surround", only for a decoder to later decode them as "side" channels.

You kind of helped to illustrate my point. You referred to "rear" channels for surround, but for a PC there's no such thing as "rear" channels. Which channels are you referring to when you say "rear"?
https://en.wikipedia.org/wiki/Surround_sound#Standard_speaker_channels

Due to the wave file channel assignments, "back" was often used for 5.1ch "surround" in the early days as "BL/BR" are next in the order of things (see the above link), and before wav format extensible came along to describe the channel layout properly there was no other option, but that was a long time ago and it doesn't make sense in relation to 7.1ch, so the convention has changed to using the "side" channels for 5.1ch surround instead (see the above link again), and as I said in my previous post, "S" can mean "side" or "surround" but either way the speaker placement is the same for both 5.1ch and 7.1ch. When you use the "back" speakers for "surround" in a 5.1ch setup they're not in the same physical location as the "back" speakers in a 7.1ch setup. Add to that a description of "rear" for "surround" and there's a tad more ambiguity as to which channels are being used when it could be either.

In my opinion, when decoding 7.1ch audio foobar2000 should be describing the "back" channels as "back, not "rear", and if foobar2000 is decoding the 5.1ch surround channels as "back" then it's probably going against current convention (labelling them as "rear" indicates they're being decoded as "back").
There may be a perfectly logical reason for that. Probably backwards compatibility with older soundcards that expect the "back" channels to contain 5.1ch "surround" audio. I know the LAV audio decoder decodes to the "side" channels by default these days, because it has an option labelled "use legacy 5.1ch layout" to force it to decode the "surround" channels as "back" instead, and while it hadn't occurred to me until now, maybe a similar option would be a good idea for foobar2000 and the output meters could then display "S" or "B" accordingly and "R" would probably be obsolete.

Re - the plugins that can re-order channels.... I have the Matrix Mixer DSP installed and use it regularly (mostly for down-mixing to stereo).... but it makes no mention of "rear" channels, only "side" and "back". I also have the Channel Mixer DSP which describes the surround channels as "R", and while I'd have to check (ambiguity once again) I assume that means as far as it's concerned the 5.1ch "surround" channels should be in the "back" channels. I don't think I've actually used the Channel Mixer DSP, but like the DSP to which you referred, it probably wouldn't work with "surround" in the "sides".

Rather than complain, I've tested a lot of different lossy codecs and channel layouts, and foobar2000 decodes all lossy 5.1ch "surround" as RL/RR, which means it's decoding the surround channels as "back" and calling them "rear", except for DST which it decodes as SL/SR, which means it's decoding the "surround" channels as "side". I don't know why... I don't think there's a law.... it's probably convention.... but am I supposed to move the surround speakers or use a different sound-card for DTS? Why isn't it consistent (I'd actually like to know)?
MediaInfo moved to describing the "surround" channels as "side" a while ago (there was a  discussion about it at doom9 at the time), except for Opus, where it uses "rear". Maybe that's an Opus thing, maybe it's a mistake, I'm not sure.

Anyway, I hadn't intended for this post to be an essay, but to me it no longer makes much sense to use "rear" instead of "back", because that's all that's happening.... When foobar2000 decodes as "back" it calls those channels "R" instead, but I think it'd be better if it followed wave file channel naming. And for it to decode to "side" instead. Given "R" always means "back" to "foobar2000" why not use "B"?

PS. The above decoding ambiguity generally only applies to lossy formats which follow DTS/AC3 convention and have "surround" channels. Lossless formats should follow wave file convention and the "surround" channels can be encoded as either "side" or "back", and decoders should decode them as "side" or "back" accordingly. foobar2000 does, although it still insists on called the "back" channels "R", and I'm easily confused. ;)

Re: Why are the "back" surround channels labelled "R"?

Reply #5 –
First time I read that rear channels are supposed to be called "back". They have always been labeled rear in sound cards and that's what Windows calls them too: .

Re: Why are the "back" surround channels labelled "R"?

Reply #6 –
Well.... what the speakers should be called aside.... according the the wave file channel layout the rear surround channels are called "back".

Mind you in the surround sound channel labelling wars, does a THX image top a Microsoft screenshot?

http://www.thx.com/consumer/home-entertainment/home-theater/surround-sound-speaker-set-up/
The forum seems to be resizing the pic down, but "Surround Left & Right (SL & SR)" and "Surround Back Left & Right  (SBL & SBR)" is how they describe 7.1ch.

I asked Dolby:
http://www.dolby.com/in/en/guide/surround-sound-speaker-setup/7-1-setup.html
They say "Left and Right Surround Speakers" and "Left and Right Back Speakers" for 7.1ch.

The question remains.... why does foobar2000 decode most lossy 5.1ch to the rear/back channels instead of surround/side channels?
I assume it's the backwards compatibility thing I mentioned earlier, but why is DTS different?

Back surround speakers are mentioned here, but not rear:
http://www.howtogeek.com/137896/how-to-place-your-speakers-to-maximize-your-home-theater-experience/

MediaInfo's in my corner:


LAV Audio:


ffdshow:


MPC-HC, MPC-BE, Potplayer, AC3 filter..... also use "back", but I won't keep posting screenshots. ;)

I'll confess my Realtek sound card labels them "side" and "rear", but they're probably just copying Microsoft, so it's Microsoft and foobar2000 vs the rest of the world (except Realtek).

My argument is largely based on consistency. The "side" channels in your 7.1ch layout.... when you switch to 5.1ch.... are they still side, or surround or are they "rear". I'm just curious, as obviously foobar2000 would generally decode them as "rear".
For 7.1ch if the back speakers are rear, it doesn't make sense for the side speakers to be rear for 5.1ch. At least not to me.

When 5.1ch is decoded, the surround channels must be decoded as side or back on a PC. There's no "rear" wave channel assignment and my preference would be to use the wave channel labelling because there's no ambiguity.

Plus, also, and in addition to that......
ffmpeg uses "back" and foobar2000 uses ffmpeg to decode. Not that it prevents foobar2000 from doing it's own thing, I'm just saying though.... https://trac.ffmpeg.org/wiki/AudioChannelManipulation#Layouts
And I'd be remiss not to point out, that while newer Windows might present the surround channels in a way Microsoft thinks makes nicer window dressing (no pun intended), down in it's internals there be no rear.
https://msdn.microsoft.com/ru-ru/subscriptions/ff537083

Mind you things change. I'm still running XP and I think the default 7.1ch layout is 7.1ch (wide) with the channel order being exactly the same as the wave file channel order:
FL FR FC LFE BL BR FLC FRC (the last two being front left centre and front right centre)
Newer Windows doesn't even support it and my sound card expects the more standard 7.1ch layout shown in your picture anyway, so it doesn't downmix 7.1ch correctly. From memory I think there's channels missing. Or I have to use the 7.1ch "hack" and encode 7.1ch as 7.1ch (wide). I think that's the problem, although I've never bothered trying to work out exactly what's going on or correct it (if I can, aside from the "hack") as I get the player to downmix anyway. Unfortunately I'm not seeing tooltip labels for the speakers.

Fun and games....

Re: Why are the "back" surround channels labelled "R"?

Reply #7 –
Rear means back.  Such as the back of the room or behind.

There is two types of 5.1 setups.  The half-circle one is what the movies standardized and used and then there is the full circle one (which could probably be used if the side speakers were missing or not functional in the full circle 7.1 setup).

Stereo equipment sometimes labels them as rear speakers as well.

The sound card line out color code is
Green - Front
Orange - Center / LFE
Black - Rear (back)
Gray - Side

My 5.1 speaker set only has the first 3 (no gray).  Likewise my sound card drivers labels 5.1 as having back channels and no side channels.  Yes they're surround channels and it is a source of confusion to most, but there is two kinds of 5.1 setups as well.

If you can, just use 7.1 instead.  But you be aware that there's two kinds of 7.1 setups (one half circle, used in large cinema halls but wasn't as widely used as Dolby and DTS 5.1 were at the time, it was a system by Sony that never saw a home version) and the more recent one to get fully standardized by the movies and see home use (full circle).

Re: Why are the "back" surround channels labelled "R"?

Reply #8 –
Yeah the surround setup for movie theatres is different to the setups for home theatre, but the latter is really all we're concerned about. And as per the links in my previous post, both THX and Dolby say that in a 5.1ch surround setup, the surround speakers should be either side of the listener, or maybe a little further back, but the 5.1ch surround speakers are "side" speakers according to Dolby. For a home theatre setup I don't think it's ever been any different. http://www.dolby.com/in/en/guide/surround-sound-speaker-setup/5-1-setup.html

Quote
My 5.1 speaker set only has the first 3 (no gray). Likewise my sound card drivers labels 5.1 as having back channels and no side channels. Yes they're surround channels and it is a source of confusion to most, but there is two kinds of 5.1 setups as well.

I played around with my soundcard a little. I've only got stereo speakers plugged into it but it lets me assign any speaker to any output. Keep in mind though I'm using an old PC. It'd be in the "legacy" category, and if I mention it's running XP in a forum I take a huge risk I'll be told off by the OS police and having someone inform me as to the year it was released, but anyway......

When I tell my sound card I want it to run in 5.1ch mode, it refuses to acknowledge the "side" speakers can have any output, even when I manually select them. It does acknowledge the speakers as "rear" speakers if I tell it to though, but then it promptly labels them LB and RB, which I'm going to boldly assume means left/right 'back" and it snubs it's nose at Dolby and THX by showing the surround speakers as being behind the listener.





Dolby and THX say the extra speakers in a 7.1ch setup are "back" surround speakers that enhance the existing surround speakers at the sides (in fact for THX they're placed together directly behind the listener), but thanks to the limitations of the wave file channel order at the time, when I select 7.1ch for my sound card configuration the extra channels are shown to appear at the sides..... in a home theatre setup it's visually wrong.

I mention my legacy sound card and previous decade OS as an example of the PC originally being a surround sound compromise which it no longer needs to be, and why anyone running a recent version of Windows would even contemplate the idea of considering disagreeing is beyond me. Is it because nobody at Microsoft changed the tooltip Windows displays for the surround configurations? :)

These days the surround/side channels can be decodes as "side", the back speakers can be decoded as back, and "rear" is an ambiguity. Mind you it's probably not the end of the world if "back" is forever referred to as "rear" as long as it only refers to the "back" channels and not "surround", but foobar2000 still decodes surround as "back" and calls it "rear" when it probably should be decoded it as "side" these days.... unless it's DTS, for reasons yet to be determined.
"Rear" should be relegated to Microsoft legacy terminology.... in my humble opinion.... like my OS, which was apparently first released in 2001.... or so I'm told.

For the record, there's actually three 7.1ch layouts. There's a screenshot of Windows displaying one of them in my previous post.
For two layouts the extra surround speakers go at the front between the stereo speakers, and for one of those the surrounds are in the side channels, while for the other they're in the 'back" channels, and there's the home theatre layout where the extra surround speakers go behind the listener, it being the only layout most of us are interested in.
I'm not sure why there's two 7.1ch layouts with the speakers at the front. Maybe Microsoft invented one as a compromise between the movie theatre layout and the home theatre layout to work around the PC limitations at the time, decided to move the surround channels back a bit, called them "rear", and planned to market the whole thing as "Microsoft Surround" encoded with WMA.... while the existing surround layouts did Netscape impersonations.
The reality is probably the same side/back ambiguity that existed for 5.1ch, but I do enjoy a good conspiracy theory...... ;)

Re: Why are the "back" surround channels labelled "R"?

Reply #9 –
Quote from: yetanotherid on
These days the surround/side channels can be decodes as "side", the back speakers can be decoded as back, and "rear" is an ambiguity. Mind you it's probably not the end of the world if "back" is forever referred to as "rear" as long as it only refers to the "back" channels and not "surround", but foobar2000 still decodes surround as "back" and calls it "rear" when it probably should be decoded it as "side" these days.... unless it's DTS, for reasons yet to be determined.
"Rear" should be relegated to Microsoft legacy terminology.... in my humble opinion.... like my OS, which was apparently first released in 2001.... or so I'm told.

It's how those input components are coded.  foobar2000 is outputting what it is given through those input components unless a DSP changes the channel layout, downmixes them together, or upmixes them.  foobar2000 itself isn't going to change what it's given through an input component.  If a component reads a file and says this is the channel layout "FL, FC, FR, LFE, BL, BR" then that's what you'll get.  Likewise if a component says the file has this channel layout "FL, FC, FR, LFE, SL, SR" then that's what you get.

Your operating system was released in 2001 and yes it's full of holes.  I hope you're not connected to the internet with that operating system.

Re: Why are the "back" surround channels labelled "R"?

Reply #10 –
What your saying is exactly how it doesn't work for lossy formats and close to how it doesn't work for lossless formats.

Lossy formats don't use back channels, and they don't use side channels, they only use surround channels. They don't store information telling the decoder which channels went in, so it's up to the decoder how they're decoded (or maybe the user).

Look at the QAAC 5.1ch assignments. It'll accept both FL, FC, FR, LFE, BL, BR and FL, FC, FR, LFE, SL, SR and encode them both as 5.1ch surround..... C L R Ls Rs LFE.
How would the decoder know which channels were input as the surround channels when the audio was encoded? Open any 5.1ch AAC audio with foobar2000 and tell me it's not being decoded as back/rear. Open the same AAC with LAV audio and it'll be "side".
https://github.com/nu774/qaac/wiki/Multichannel--handling

Even for lossless formats, where in theory there should be no ambiguity (because the wave file channel layouts are used), the rules still aren't always followed for one reason or another. Take a 5.1ch wave file with "side" for surround, encode it as flac with ffmpeg, then decode it with foobar2000 and watch the "side" channels magically transform to back/rear.



At one stage I encoded a bunch of multichannel files with a bunch of codecs and tried to determine which were encoding the audio using the correct channel layouts. I hit a stumbling block when I realised I couldn't necessarily rely on the audio being decoded correctly. I have a recent thread here somewhere where I've attached three samples of ALAC that foobar2000 decodes incorrectly.

Anyway, this thread wasn't intended to be about encoders/decoders that don't play by the rules, but if anything it's more about what the rules should be.

Quote
Your operating system was released in 2001 and yes it's full of holes. I hope you're not connected to the internet with that operating system.

I'm fairly confident I'm proof that 99.9% of infections these days are the result of the user given something permission to infect a PC. Clicking "okay" without thinking being the main culprit.

I haven't run Windows Update for a couple of years. I haven't run an antivirus program for about eight years. I stopped running a software firewall about ten years ago (I'm behind a router). This PC runs 24/7 and it's always connected to the internet. My broswer is up to date. I travel to the dark corners of the internet. I've been infected once in about 15 years. It was my fault. I didn't think and let some very persistent crapware install along with some free software.
How do I know I've not been infected? Once every couple of years (I'm way overdue at the moment) I restore a previous image of my C partition. I then run Windows update, update any software as required, make a new image and I'm done for the next couple of years. Before restoring the previous image though, I always install antivirus software and run a full scan. Just to be sure. A couple of times I've scanned twice with different antivirus programs. Those scans have never found anything worse than a "naughty cookie".... if there really is such a thing.

Re: Why are the "back" surround channels labelled "R"?

Reply #11 –
Work just fine for me.

A 5.1 FLAC file with Side Surround Left & Right.

I just used the FLAC Front-end encoder with a properly encoded wav file type that foobar2000 outputs.

Re: Why are the "back" surround channels labelled "R"?

Reply #12 –
Quote from: yetanotherid on
[..] both THX and Dolby say that in a 5.1ch surround setup, the surround speakers should be either side of the listener, or maybe a little further back, but the 5.1ch surround speakers are "side" speakers according to Dolby. http://www.dolby.com/in/en/guide/surround-sound-speaker-setup/5-1-setup.html
In a 5.1 configuration there were no side speakers. Dolby, for one, used to call the rear speakers (Left and Right) "Surround" before they went beyond 5.1 (see the link you provided and scroll a bit till the last picture, to see what that would look like). Nowadays there is a distinction between Back and Side (or even Height), when going beyond 5.1.

To play back 5.1 material on a 7.1 setup you should "upmix", e.g. with Prologic IIx (or NEO:6), which both have a Music or a Movie / Cinema mode. In Music mode the "rear" information is placed somewhere between the Back and the Side, about where a speaker would be in a 5.1 setup.
In theory, there is no difference between theory and practice. In practice there is.

Re: Why are the "back" surround channels labelled "R"?

Reply #13 –
Quote from: Chibisteven on
Work just fine for me.
A 5.1 FLAC file with Side Surround Left & Right.
I just used the FLAC Front-end encoder with a properly encoded wav file type that foobar2000 outputs.

Hence my specifying a flac file encoded with ffmpeg. The Devil's in the details, and the channel layouts.

ffmpeg flac encoded as "back" has a WAVEFORMATEXTENSIBLE_CHANNEL_MASK tag of 0x3f, although right now  I can't remember how to translate that into channel-layout-speak. foobar2000 decodes as back.
ffmpeg flac encoded as "side" has no WAVEFORMATEXTENSIBLE_CHANNEL_MASK tag. foobar chooses "back" when decoding. I assume ffmpeg isn't ready to acknowledge that layout exists yet.

The official flac writes the WAVEFORMATEXTENSIBLE_CHANNEL_MASK info for both layouts, it would seem. Flac wasn't born able to write the WAVEFORMATEXTENSIBLE_CHANNEL_MASK data though. It evolved.

Try opening your flac file with Mp3Tag and removing the flac tag completely. After a while I learned to be more careful, because no flac tags, no WAVEFORMATEXTENSIBLE_CHANNEL_MASK info, no WAVEFORMATEXTENSIBLE_CHANNEL_MASK info, no side channels. It not a reliable way o save channels layouts in that respect. Try it and without the flac tag you'll see your  "S" channels become "R" channels, as if by magic.

From the mouth of the horse:
https://xiph.org/flac/format.html#frame_header
<4> Channel assignment
0000-0111 : (number of independent channels)-1. Where defined, the channel order follows SMPTE/ITU-R recommendations. The assignments are as follows:
1 channel: mono
2 channels: left, right
3 channels: left, right, center
4 channels: front left, front right, back left, back right
5 channels: front left, front right, front center, back/surround left, back/surround right
6 channels: front left, front right, front center, LFE, back/surround left, back/surround right
7 channels: front left, front right, front center, LFE, back center, side left, side right
8 channels: front left, front right, front center, LFE, back left, back right, side left, side right

There's still no official 5.1ch "side" layout. The decoder either reads the tags if they're written and plays along or it doesn't.

Quote from: GeSomeone on
In a 5.1 configuration there were no side speakers. Dolby, for one, used to call the rear speakers (Left and Right) "Surround" before they went beyond 5.1 (see the link you provided and scroll a bit till the last picture, to see what that would look like). Nowadays there is a distinction between Back and Side (or even Height), when going beyond 5.1.

The "no surround channels on a PC" ambiguity is the reason for this thread.
Is that link taking your browser to a different site on another internet in an alternative universe? I'm seeing a picture with the surround speaks placed each side.



Quote from: Chibisteven on
To play back 5.1 material on a 7.1 setup you should "upmix", e.g. with Prologic IIx (or NEO:6), which both have a Music or a Movie / Cinema mode. In Music mode the "rear" information is placed somewhere between the Back and the Side, about where a speaker would be in a 5.1 setup.

Upmixing probably should be illegal and punishable by death.
I'll confess I don't know what "music" mode refers to exactly.

Re: Why are the "back" surround channels labelled "R"?

Reply #14 –
Quote from: yetanotherid on
Quote from: GeSomeone on
In a 5.1 configuration there were no side speakers. Dolby, for one, used to call the rear speakers (Left and Right) "Surround" before they went beyond 5.1 (see the link you provided and scroll a bit till the last picture, to see what that would look like).

Is that link taking your browser to a different site on another internet in an alternative universe? I'm seeing a picture with the surround speaks placed each side.
Yes, sort of, there is something weird with that page. Anyway, What I saw was something like this (and I opened the info for the Surrounds as well).


I agree it is a Windows thing, IMO foobar2000 is not to blame.
In theory, there is no difference between theory and practice. In practice there is.