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Atmos and TrueHD 7.1 playback on 5.1 systems - Tests, Results, questions, experiences

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HomerJAU

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Hopefully we’ll get a definitive answer to what happens when users playback Atmos and TrueHD 7.1 mixes on non Atmos/7.1 surround systems (typically 5.1, maybe some Quad only system users too).

I have a set of Dolby Atmos channel identification test files with encoding for: 5.1.2, 5.1.4, 7.1.2, 7.1.4 and 9.1.4. I also have a TrueHD 7.1 channel identification file.

I have two surround systems. One is 7.1.4 and the other 5.1. Both systems have Denon AVRs with Atmos decoders. I can play all the test files via HDMI Passthrough sending the raw Atmos/TrueHD bitstream to the AVRs for decoding.

The Tests:
Playback each file on my 5.1 system and listen to each channel. Can I hear all the channels in each test file?

Here are the Dolby Atmos Channel Test files from an official Dolby Atmos Demo Disc. Each file contains a 10 sec discrete signal to each channel in turn:

DISCLAIMER: Fair use is claimed on all test files, as their purpose is only for the promotion of Dolby Atmos music, testing and technical evaluation for our members. QuadraphonicQuad is a non-profit, non-sponsored website.

The Results:
TrueHD 7.1:
Yes. All channels can be heard. The rear channels are heard in the side surround speakers. Conclusion: If you have a TrueHD decoder all channels are mixed into the 5.1 output, surrounds are blended.

Atmos 7.1.2: Yes. All channels can be heard. The rear channels are heard in the side surround speakers And the ceilings are mixed into my side surround speakers. Conclusion: If you have an Atmos decoder all channels are mixed into the 5.1 output, surrounds are blended along with top/ceilings.

Need test results for a user with an old TrueHD decoder (and no Atmos decoder) to test what happens to the two ceiling channels (I’d think the Atmos ceilings will be ignored but you’ll get the 7.1 bed channels as per TrueHD test above)

Atmos 7.1.4: Yes. All channels can be heard. The rear channels are heard in the side surround speakers, rear ceilings in side speakers and front ceiling channels into front L/R speakers. Conclusion: If you have an Atmos decoder all channels are mixed into the 5.1 output, surrounds are blended along with top/ceilings.

Need test results for a user with an old TrueHD decoder (and no Atmos decoder) to test what happens to the four ceiling channels (I’d think the Atmos ceilings will be ignored but you’ll get the 7.1 bed channels as per TrueHD test above)

NOTE: These results should be consistent with playing back Atmos and TrueHD 7.1 from blu-ray discs since the test decoding was done on an AVR (and would be same on a BD player with bit streaming or if the BD player is used to decode to PCM)
 
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J. PUPSTER

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All the MKV files played correctly for me except I got no sound for a 9.1.6 system which may be more than my player handles, I'll have to check the specs. Everything played as MLP down-mixed to my 5.1 system.

Used - Oppo UDP-205 analog out to my Marantz SR8500. I was streaming the files on my home network CAT-5 cabling from my Windows 10 NUC to the Oppo under the Network Menu.
 
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J. PUPSTER

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Here’s a point I’d like to try and make about the differences between an Atmos mix vs. an Atmos down mix for arguments sake.
If my thinking doesn’t sound logical or reasonable, please let me know why.

What I’m saying here is not a reflection on the abilities of a good Atmos mix, played on a system with full Atmos capabilities, created by a competent mix engineer. I’ll assume that can sound really great, provided it coincides with your expectations of how it should sound, appropriate and relevant to the style of music being played.

What I’m concerned with (as I’ve tried to express over at the Goats Head Soup thread) is once the codec and device, either Blu-ray player or AVR etc., wholesale down mixes to a traditional 5.1 system, you lose the intent and control the mix engineer had in mind for that music, for not only the Atmos mix, but what the 5.1 mix would have been also. This is also mainly addressing the fact (hopefully not a trend) of the Goats Head Soup release, not providing a “dedicated” 5.1 DTS-HD Master Audio mix.
I’m going to call it the “Atmos Down-Mix Unintentional X” factor - ADMUX for short.

This is based on what my current understanding of the differences between an Atmos vs. a traditional 5.1 mix are. One important caveat is that I haven’t actually heard a legitimate Atmos mix, But I feel given the visual diagrams by DOLBY of how projected object oriented sound positioning in a room should work, I have a decent enough understanding.

Here is one example.

First, let’s just assume, that we have a good set of full range speakers operating in a fairly adequately-neutrally acoustic room, and you're positioned in the sweet spot ( for traditional 5.1 non object oriented comparisons.)

Take a mix similar to what Steve Wilson did on the Jethro Tull album 'This Was'; where there were many instances he mixed instruments (mainly guitars IIRC) into side Phantom Center positions. But let’s say something similar was done by Bob Clearmountain for an Atmos mix of some instrument, even farther into the middle of the room, 3 feet from the left side of the speaker plain and at 5 feet off the ground and then rotating through to a different position using object orientation. But with a 5.1 system you no longer have the side Surround or Height speakers to guide that along, and that sound from the Atmos mix now just gets thrown into your Left Rear speaker and has no help from the other missing Atmos speakers, for that special object oriented position that Bob had so lovingly worked hard on. So not only has it been put out of room position, it’s also flattened it out directionally. Now all this may not be that noticeable to an instrument simple Rock band like The Rolling Stones; and let's be real here, do we really know what the mix engineer was going for once it gets into our own speaker situation and room acoustics?
But now consider a larger more complex band like Gordon Goodwin's Big Phat Band; and I believe it will become much more problematic to achieve any semblance of what the Atmos mix would have sounded like in a 5.1 system.

So this is an entirely different mix and out of control of what Bob (or Giles) had intended; all done on a systematically wholesale level.

And why I believe this is all so important is; what if the labels and Dolby are making that big push to drive us 5.1 guys into the Atmos market and start only producing Blu-rays with the down mix option. Then the ADMUX factor is going to be a huge problem.
 

HomerJAU

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So this is an entirely different mix and out of control of what Bob (or Giles) had intended
I don’t think you need to worry too much about this if you have a 5.1 system. From my tests we can see Dolby’s promise of backward compatibility is correct.

If a mixer has intended his/her Atmos mix to be heard in Atmos with an Atmos speaker array the only way you’ll hear this as designed is installing extra (height) speakers and listening to the Atmos mix.

Isn’t a bit like the old movie aspect ratio debate about what the director and/or cinematographer intended? You could watch a widescreen movie on a 4:3 TV screen and see the movie with a little missing off the sides, you don’t miss anything in the story, but it’s not what the movie maker intended. Solution? Upgrade to a widescreen TV. With Atmos on a 5.1 system your hearing the ‘story‘, but missing the immersion the mixer intended. If you want to hear as intended you need to upgrade.

The point is, you CAN listen to Atmos in 5.1. It is still a valid surround mix, just with original mix positioning being moved to the appropriate floor speakers. That’s way better than actually discarding the extra Atmos audio info.
 

bracelis

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Atmos 7.1.4: Yes. All channels can be heard. .... And the front ceilings are mixed into my side surround speakers,
Did you mean the rear ceilings ?

Need test results for a user with an old TrueHD decoder (and no Atmos decoder) to test what happens to the four ceiling channels (I’d think the Atmos ceilings will be ignored but you’ll get the 7.1 bed channels as per TrueHD test above)
The ceilings should not be ignored / lost, even without an Atmos decoder.
I tested the 7.1.4 Atmos test tones from the Dolby Atmos demo disc using JRiver on a Windows PC ( I let JRiver do the decoding -- it does NOT decode Atmos) and sent the audio to the computer's speakers -- the front ceiling audio are sent to the front speakers, and the rear ceilings are sent to the surround speakers.

!
"In order to maintain compatibility with millions of devices in consumer homes, Dolby Atmos in these codecs is implemented as a backwards-compatible extension. Dolby Atmos data is hidden within the bitstream and can be decoded by a Dolby Atmos-compatible A/V Receiver, soundbar or television. Non-Dolby Atmos capable devices will decode a 5.1-ch or 7.1-ch version from the Dolby Digital Plus or Dolby TrueHD bitstreams. "

I believe what the above means is that Dolby-Atmos compatible decoders are able to 'see' and extract the Atmos objects, while non-Atmos decoders cannot 'see' them separately and they are simply mixed into the 5.1 or 7.1 channels.
 
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HomerJAU

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while non-Atmos decoders cannot 'see' them separately and they are simply mixed into the 5.1 or 7.1 channels.
Since the Atmos heights is additional metadata (added post TrueHD) I presume non-Atmos decoders simply cannot ‘see‘ Atmos heights data and therefore won’t remix to bed channels. Testing will confirm.
 

salsdali

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- Slim Shady

Imagine a Master painter paints a picture in a certain light. He paints in the morning, he paints at night, all the while the light changes in his studio, home, by season.

If you view that painting with those exact changes that the painter experienced you will see the same picture.

If you look at the picture under your light, time of day, season etc you will see a different picture.

The only way to capture what an artist, mixer, engineer INTENDED is for you to have the exact same setup / listening (viewing) environment.

The brain is good at making approximations so you can get close but it will never be exact.

Will this matter? Who's to say?
 

JonUrban

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So I downloaded the mkv files and put them on a USB stick to see what my Oppo/Denon AVRs would do with them.

Well, the Oppo doesn't see them. It's a 103 so maybe it's too old.

However, I did playback the files on my PC system and here's what I got:

7.1.4
5.1.4
7.1.2
5.1.2
TrueHDChannelTest - All of these worked fine using VLC Media Player. Since I only have 5.1 speakers installed, the VLC sent the audio from the channels that did not exist to existing channels on its own. Very cool

9.1.6 - Nothing. Silence. It didn't do a thing. The graphics worked, the speakers were highlighted, but I heard nothing.
 

JonUrban

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Thanks all. I'll try it again. This time I'll look for video, not audio. DUH!

:giggle:
 

JonUrban

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Alright, I tried it again, this time looking for video! Here's what I got for results.

This is a 5.1 system. Oppo 103D and a Denon AVR-4311CI

7.1.4 - The height channels were heard in the rears
5.1.4 - The front height channels were heard in the fronts, the rear heights in the rears
7.1.2 - All surround channels piped into the rears, heights were in the rears as well
5.1.2 - All surround channels piped into the rears, front heights in the fronts, rear heights in the rears
9.1.6 - Same as PC. No audio at all. The video plays with speaker indication, but nothing but silence
DOLBY TRUE HD DEMO - Plays fine, all 4 surrounds are heard in the rears, the front heights in the fronts and the rear heights in the rears

The receiver never says Dolby TrueHD like it does when I play a BluRay, it says BD - MultiChannel Input

Garry, I hope that helps
 
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