Q about multi-channel routing

[tifune]

I'm having a hard time finding info about AVR channel routing as it relates to mixed speaker layouts. What I mean is, if I have something like rear heights but no surround backs, will the AVR send surround back info to rear heights? Or simply not play those tracks and the rear heights sound the same as they would with or without surround backs?

Would DTS, Auro, Dolby handle the situation differently? I suspect it's codec dependent, but just in case, would Yamaha vs Denon/Marantz handle it differently?

Expanding on my first example, if I only have 1 surround back does that influence rear height playback?

If I had no rear/backs, would that data be transferred into the surrounds? Not sure if the data is fenced - meaning, surround back and rear heights are (partially) interchangeable but surround back would never be sent to surrounds, no matter what.

Thank you!

 

[Soundmixer]

" What I mean is, if I have something like rear heights but no surround backs, will the AVR send surround back info to rear heights?"

The answer is no.

"Expanding on my first example, if I only have 1 surround back does that influence rear height playback? "

The answer to this is no. However, with only one rear back speaker, you are only going to playback one channel of two and that is not optimal.

"If I had no rear/backs, would that data be transferred into the surrounds?"

The answer is also no, that information would be discarded.

Nothing is interchangeable with Atmos or X, or TrueHD or DTS-HD-Master audio. You tell the processor what speakers you have and where they are, and it will only send the corresponding data in those channels to the speakers.

 

[Sancus]

The answer is also no, that information would be discarded.

Nothing is interchangeable with Atmos or X, or TrueHD or DTS-HD-Master audio. You tell the processor what speakers you have and where they are, and it will only send the corresponding data in those channels to the speakers.

This is completely and totally incorrect. The whole point of Atmos is that you define sound emitting objects in 3D space and it downmixes them to match your speaker setup. It doesn't just discard information.

Even with normal non-object formats, receivers will downmix all channels to the available channels. Otherwise, you'd get no dialogue if you tried to play a movie with no center channel, and we all know that doesn't happen...

If I had no rear/backs, would that data be transferred into the surrounds? Not sure if the data is fenced - meaning, surround back and rear heights are (partially) interchangeable but surround back would never be sent to surrounds, no matter what.

Generally speaking, no, rear surround sound would get mixed into the surrounds if you don't have rears. Downmixing doesn't move sound from ear-level to height-level.

I'm not sure exactly how it would behave with a true Atmos mix(not pinned 7.1.4). It is possible that some would end up in the rear heights. It's very hard to say without testing because of the way Atmos works, and it would probably vary based on the content.

 

[tifune]

This is completely and totally incorrect. The whole point of Atmos is that you define sound emitting objects in 3D space and it downmixes them to match your speaker setup. It doesn't just discard information.

Even with normal non-object formats, receivers will downmix all channels to the available channels. Otherwise, you'd get no dialogue if you tried to play a movie with no center channel, and we all know that doesn't happen...

Thanks! The Monolith HTP-1 manual (p. 22) outlines a few ways in which channel information gets "shifted" depending on the speaker layout, but sometimes it seems the HTP-1 is making those decisions and other times it's the codec. That prompted me to look a little deeper and I was surprised there doesn't seem to be any readily-available info out there from the respective codec authors.

In my situation, I don't have room to setup surround back the proper way so I was just trying to determine if it makes more sense to put 1 speaker, 2 very small speakers (KH80), or a small soundbar right behind the sitting position. Or maybe just skip it altogether and setup my rear heights on the surround back channels. So far I've opted for a Kef 7003 because it's unobtrusive but , like many, always wondering how I can make it "better".

 

[Soundmixer]

This is completely and totally incorrect. The whole point of Atmos is that you define sound emitting objects in 3D space and it downmixes them to match your speaker setup. It doesn't just discard information."

Sorry, but Atmos does not downmix height information down to the ear-level speakers. If there are no height speakers defined in the processor, the height speakers output is discarded. It does not fold down into any other channels. Also, Atmos does not fold down and remix its rear information to the side speakers. There is no folding down process at all with Atmos, Atmos just uses whatever speaker positions are defined in the processor, and uses whatever speakers it needs to position an object into a specific point in 3D space. Folding down is associated with channel-based systems, and Atmos is not a channel-based system.

"Even with normal non-object formats, receivers will downmix all channels to the available channels. Otherwise, you'd get no dialogue if you tried to play a movie with no center channel, and we all know that doesn't happen..."

This is incorrect. If I have a 7.1 soundtrack being played through a 5.1 system, the rear information is discarded. We are talking about discrete information here, not matrixed. Processors don't fold discrete information from one channel to another because there could be phase issues that crop up. If you tried to play a 5.1 discrete track through a system with no center speaker, there would be no dialog. If you tell the processor there is no center speaker, THEN it splits the dialog between the two front channels.

 

[Sancus]

Atmos just uses whatever speaker positions are defined in the processor, and uses whatever speakers it needs to position an object into a specific point in 3D space.

That is exactly what I said, yes. Downmixing is a generic term, regardless of the mechanism.

This is incorrect. If I have a 7.1 soundtrack being played through a 5.1 system, the rear information is discarded. We are talking about discrete information here, not matrixed. Processors don't fold discrete information from one channel to another because there could be phase issues that crop up. If you tried to play a 5.1 discrete track through a system with no center speaker, there would be no dialog. If you tell the processor there is no center speaker, THEN it splits the dialog between the two front channels.

Why would you play a 5.1 track(or any track) without telling the processor what your speaker setup is? You say information is discarded, and then contradict yourself by saying the processor downmixes so the audio isn't lost. Which is correct, yes. No audio is lost from a multi-channel soundtrack if played with fewer channels because the processor downmixes.

The way that works is different in discrete channel audio and Atmos, yes, but it happens either way. The OP's question was about real results on a real system, not about semantics.

Thanks! The Monolith HTP-1 manual (p. 22) outlines a few ways in which channel information gets "shifted" depending on the speaker layout, but sometimes it seems the HTP-1 is making those decisions and other times it's the codec. That prompted me to look a little deeper and I was surprised there doesn't seem to be any readily-available info out there from the respective codec authors.

In my situation, I don't have room to setup surround back the proper way so I was just trying to determine if it makes more sense to put 1 speaker, 2 very small speakers (KH80), or a small soundbar right behind the sitting position. Or maybe just skip it altogether and setup my rear heights on the surround back channels. So far I've opted for a Kef 7003 because it's unobtrusive but , like many, always wondering how I can make it "better".

Very little information is available because those algorithms are proprietary(at least for Dolby). So you pretty much have to test. And yes, I agree, it is frustrating when trying to decide on your speaker layout.

I wouldn't use a single rear speaker. It was discarded from early surround formats(6.1) because sound directly behind you from a single source can sound like it's coming from in front of you. That said, if you try it, and you don't experience that effect, maybe it's fine. But that's why 2 rear speakers were standardized. A soundbar might help with this due to spreading out the source.

P.S. There are test tone files you can use to confirm behaviour, such as 7.1 TrueHD and DTS 7.1.4 Object Emulator. Atmos 7.1.4 and 9.1.6 test files exist, but playback of Atmos in .mkv files only works on certain devices.

 

[tifune]

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I wouldn't use a single rear speaker. It was discarded from early surround formats(6.1) because sound directly behind you from a single source can sound like it's coming from in front of you. That said, if you try it, and you don't experience that effect, maybe it's fine. But that's why 2 rear speakers were standardized. A soundbar might help with this due to spreading out the source.

P.S. There are test tone files you can use to confirm behaviour, such as 7.1 TrueHD and DTS 7.1.4 Object Emulator. Atmos 7.1.4 and 9.1.6 test files exist, but playback of Atmos in .mkv files only works on certain devices.

These test files are great, thank you! My source is a HTPC so I'm pretty confident I can get them to work somehow.

The sound bar does spread the sound a little as you anticipated, and combined with rear height speakers it's good enough for Auro upmixing. But for some reason Audyssey always detects it as being 27ft away even though it's literally 2ft from primary listening position.

Not sure what that's about but the same thing happens when using Kef LSX as front height even though they're only 4ft above FL/R which Audyssey measures accurately at 12ft. My permanent setup won't be this random pish posh, it's just stuff I had lying around to test surround/2ch upmixing to make sure I like it before I go drilling holes all over my living room for wall mounts

 

[polmuaddib]

Too bad there aren't corresponding test files for Atmos as for 7.1 true hd. All test videos for atmos are with pink noise and not with female voice telling which channel is playing, like with old true hd test files. If there were such files for atmos, you could test it then in various configurations to see how information is routed.
Also, i believe it is impossible to create Atmos track without paying for license, right?

 

[Sancus]

These test files are great, thank you! My source is a HTPC so I'm pretty confident I can get them to work somehow.

Here are the Atmos files, as @polmuaddib said they are pink noise so it's a bit harder to tell exactly what's going on, but not that bad IMO.

7.1.4 Test
9.1.6 Test

(these links will last for 1 week)

I couldn't find them on the internet so I uploaded them myself. They are from the 2015 Dolby Atmos Bluray Demo, you can download the whole disc via this thread on AVSForum if you want, it's like 22GB though and you'll need to know what to do with a BDMV yourself.

But for some reason Audyssey always detects it as being 27ft away even though it's literally 2ft from primary listening position.

This could just be DSP delay built into the soundbar. You get the same thing with subs. Audyssey detection is just based on delay, so for example it overestimates the distance to all my Genelecs as well since they have ~3ms of delay.

Also, i believe it is impossible to create Atmos track without paying for license, right?

I think if you have a Mac you could use a 90-day trial of the Dolby Atmos Production Suite, but it's Mac-only and I don't know if there are output limitations on the trial. I don't currently have a Mac or I'd look into it.

However, it's worth noting these tests aren't going to replicate real Atmos content necessarily, because you can have more than 12-16 Atmos objects and in properly mixed Atmos content they're not necessarily in the same positions as speakers either. So any kind of test tone file for Atmos is necessarily going to be of limited use.

What would be actually useful is an interactive app that let you play sounds from any direction with a tablet interface or something, Dolby should get on that But in the absence of it, there isn't a truly realistic way to simulate/test Atmos.

 

[Soundmixer]

That is exactly what I said, yes. Downmixing is a generic term, regardless of the mechanism.

If this is exactly what you said, then you are repeating exactly what I said!!!! Also, Downmixing is not really a generic term. It is a very specific term that implies folding one channel into another. 7.1 downmixed to 5.1. 5.1 downmixed to 2.0 (etc). That is not what is happening with Atmos, and not all information is being saved when a soundtrack is played through a system with fewer speakers than channels on the soundtrack.

Why would you play a 5.1 track(or any track) without telling the processor what your speaker setup is? You say information is discarded, and then contradict yourself by saying the processor downmixes so the audio isn't lost. Which is correct, yes. No audio is lost from a multi-channel soundtrack if played with fewer channels because the processor downmixes.

The devil is in the detail bro. I will state this again. If you play a 7.1 soundtrack on a 5.1 system, the rear two channels are discarded - they are not folded into other channels (phase issues). If I played a 5.1 soundtrack on a 2.0 system, the rear channels are discarded. It is not folded down. In this case, the soundtrack is re-encoded to stereo, and only the L/R and center information survive.

"The way that works is different in discrete channel audio and Atmos, yes, but it happens either way. The OP's question was about real results on a real system, not about semantics."

You are fudging here. Sorry, but semantics is a part of the equation. If you don't get your REAL SYSTEM processes correct, you could easily leave somebody misinformed or just plain confused. That is where the semantics come into place.

The OP was clearly talking about an Atmos setup, and let's be clear here. Atmos does NOT downmix, that is not how it works. So it is clear you haven't gotten the REAL SYSTEM part right.

Just saying.....

 

[Sancus]

If you play a 7.1 soundtrack on a 5.1 system, the rear two channels are discarded - they are not folded into other channels (phase issues).

I've already posted the test files that easily disprove all your claims about "discarding", no further discussion is useful.

 

[Soundmixer]

I've already posted the test files that easily disprove all your claims about "discarding", no further discussion is useful.

Who are you trying to fool here?? These are Atmos test files, not files the prove anything about discarding. Atmos is scalable, it does not downmix, it adapts itself to the speaker set up. I have both the DTS : X and Dolby Atmos demo discs, and there is nothing on them that addresses your point.

Your feeble attempt to end this discussion with something that does not prove your point shows just how weak your point is. I would advise you to read Dolby's white paper on how Atmos works. The posturing thing...... just doesn't work.