Atmos vs 5.1

[jimfisheye]

Would you call an airplane autopilot 'random'?

No but I'd probably describe the robotic autopilot generated music more akin to listening to an airplane takeoff!

 

[kfbkfb]

aside:
To hear the DD 5.1 downmix, plug the SPDIF output from a [UHD]Blu-ray player into the SPDIF input on your A/V receiver, it might be possible to switch between the Atmos and the DD 5.1 from a [UHD]Blu-ray disc by using the A/V receiver input selector to select HDMI (containing Atmos) or SPDIF (containing DD 5.1).

https://en.wikipedia.org/wiki/S/PDIF


Kirk Bayne

 

[barfle]

Wow. Just wow. So much denial and incorrect speculation apparent in this thread.

Yeah. This is one of the nastiest conversations I’ve read on QQ. Not sure why it has to be that way.

 

[ssully]

No but I'd probably describe the robotic autopilot generated music more akin to listening to an airplane takeoff!

An algorithm that downmixes isn't 'generating' music. Nor is it operating at random. I've never heard a downmix (or upmix, of which I've heard thousands) that sounded like an airplane takeoff.

 

[jimfisheye]

An algorithm that upmixes stereo isn't 'generating' music. ...

No, it's generating artifacts. That's my problem with it!
If I want to hear the sound of wind chimes under water I'll put on an Enya album.

Like I said, I'm sure you can find something to mess with me! Someone turned me on to their upmix of Eleanor Rigby a little while ago that sounded outstanding. Giles and company should have contacted them instead for that recent science experiment they did with that Now And Then track! Which was fully the underwater windchime thing. That was also given the volume war treatment to make it sound worse than nature intended. Or maybe to distract from those artifacts?

I've heard even worse than some of those Beatles experiments too. Sometimes hard grating distortion effects - think distorted little transistor radio or guitar tube screamer stomp box. And then you get a "Huh?!" when you ask what's up with that. That's the kind of thing that makes me scratch my head!

 

[ssully]

No, it's generating artifacts. That's my problem with it!
If I want to hear the sound of wind chimes under water I'll put on an Enya album.

On this thread we were actually talking about downmixed or 'core' DD 5.1 mixes; I wrote upmix by mistake (though the same logic applies). So I corrected that post.

But I can say that in decades of using Dolby upmixers, I've never heard such artifacts -- unless I listen very unnaturally: by isolating a channel.

IOW: psychoacoustics actually works.

 

[zdjh22]

Would it be possible to encode 7.1.4 Atmos, 1kHz at each of the 11 locations in turn (.1 not needed) and then report where each of these 11 locations ends up appearing in the Dolby Digital 5.1 downmix (using the downmix defaults)?


Kirk Bayne

The Pink Floyd DSOTM and Animals Atmos BluRays have a "System Setup" under "Audio Selection" that includes an "Atmos Speaker Configuration" which lets you hear each speaker in turn from a 7.1.4 arrangement, with an accompanying animation. Let me see if I can pull that piece out of one of the BluRays and post it (assuming that is allowed).

In answer to your question, from my Oppo 203 I fed the output in both bitstream and LPCM form via HDMI to my Smyth A16 and watched the virtual speaker meters as it played. Bitstream of course is decoded as Atmos, and with a 7.1.4 Atmos listening room configured, one at a time L/C/R/Lss/Rss/Lb/Rb/Ltf/Rtf/Ltr/Rtr/SW fired in turn (as expected).

Since the Oppo 203 does not decode Atmos (does not have a built-in decoder), I presume LPCM simply sends the downmix. With a 7.1 PCM listening room configured, I saw on the meters this pattern at the corresponding labeled positions:
L: L
C: C
R: R
Lss: Lss
Rss: Rss
Lb: Lb
Rb: Rb
Ltf: L+C+Lss+Rss/2 (where Rss/2 indicates about half the level on Rss as the others)
Rtf: R+C+Lss/2+Rss
Ltr: Lss+Rss/2+Lb+Rb/2
Rtr: Lss/2+Rss+Lb/2+Rb
SW: SW

With a 5.1 PCM listening room configured, I saw on the metters this pattern:
L: L
C: C
R: R
Lss: Lb
Rss: Rb
Lb: Lb
Rb: Rb
Ltf: L+C+Lb+Rb/2
Rtf: R+C+Lb/2+Rb
Ltr: Lb+Rb/2
Rtr: Lb/2+Rb

I have no idea whether these are the downmix defaults in the Dolby Encoder, as that depends on how the Pink Floyd audio engineers prepared the setup video. I could give doing my own encode a spin, since I do have a copy that I use for encoding 7.1.4 files that I prepare in Audacity, but there are much better experts out there than me who can give better testimony about the downmix settings in the encoder.

Of course, the above is all subject to how the Atmos decoder in the A16 works (presumably a licensed and so standard decoder), and my assumption that the Oppo 203 is sending the 7.1 PCM downmix from the Atmos file (but what else could it be doing?). The 5.1 results are surely simply the results of what an A16 5.1 PCM listening room does with a 7.1 input signal. I'm not sure how to make the Oppo send a pure 5.1 PCM stream - maybe over S/PDIF?

Also, I took a look at what happens with a 15.1.8 Atmos listening room configured on the A16 listening to the 7.1.4 Atmos (bitstream). Interestingly there is a lot of multi-speaker activity, ranging from a bit of SW added to the L, C, and R front channels, to lots of mixing across the various speakers at the other positions. I did not expect that behavior from "bed" channels, figuring they would still go to their respective positions. Objects, yes, and I have seen for example isolated C-rear activity in Atmos listening rooms with that speaker configured (see my Ziggy Stardust post, for example); when the Cr is not configured, that activity is split among the nearby rear speakers as one would expect. [Note: thinking about the SW activity, I think my 15.1.8 listening room was configured with a different bass management scheme, so probably nothing to do with Atmos decoding.]

 

[zdjh22]

As promised, here are MKV files with the 7.1.4 Atmos video setup from "Animals", one with the speaker named by voice, the second with pink noise at each speaker. There are multiple audio tracks, including TrueHD and the 7.1 and 5.1 downmixes.

https://we.tl/t-pOZ8fNsVpY

 

[Owen Smith]

Using Pink Floyd DSOTM for tests of this is a mistake. There is an encoding or mixing problem of some sort with that blu ray, as discussed at least twice on QQ some time back. It's fine (music and test tones) when decoded as Atmos, but is very odd when just playing the 7.1 True HD stream. Your speaker positions match the results I got on my 5.0 system, it's all very wishy washy and "lots vaguely in the middle". On 5.0 the results are worse than 7.1, since Lss and Lb are one speaker as are Rss and Rb. Which means much of Ltf and Rtf play from behind me as your results show, which is ridiculous.

When I have my AVR decode and render the Atmos to my 5.0 system everything behaves much better, both the test tones and the music. ie Ltf goes to L, Rtf to R, Ltr to Lb, Rtr to Rb which is what I expect to happen.

When I've tried on other discs switching between straight True HD and Atmos I can't hear any difference. I absolutely can on DSOTM in many tracks, but the alarm clocks and the cash register drawers make the issues obvious.

 

[MidiMagic]

I'm beginning to believe that's a real thing. You spend big money on a non Atmos rig (or even worse, a non HDMI rig). Maybe you even had to go into debt to get it. After a few years you become bitter because the tech has moved on and your super expensive but outdated components are nearly worthless on the used market because they can't process the newest formats that everyone is raving about. Not to mention the formats the old gear can process arent being produced anymore. The easiest way to justify your original decision is to keep that old gear and convince yourself all that new tech is total crap. It makes sense. It happened with the transition from LPs to CDs, from tube TVs to flat-screens, and the transition from analog inputs to HDMI. Why wouldant it happen with the 5.1 to Atmos transition.

Or worse, you have to have multiple setups to play all of the different kinds of recordings, because they have to keep changing things. They can't pick one technology and stick with it, because the business wonks want all of the products they sell to be under patent protection. When a patent expires, they discontinue the product.

 

[zdjh22]

Using Pink Floyd DSOTM for tests of this is a mistake. There is an encoding or mixing problem of some sort with that blu ray, as discussed at least twice on QQ some time back. It's fine (music and test tones) when decoded as Atmos, but is very odd when just playing the 7.1 True HD stream. Your speaker positions match the results I got on my 5.0 system, it's all very wishy washy and "lots vaguely in the middle". On 5.0 the results are worse than 7.1, since Lss and Lb are one speaker as are Rss and Rb. Which means much of Ltf and Rtf play from behind me as your results show, which is ridiculous.

When I have my AVR decode and render the Atmos to my 5.0 system everything behaves much better, both the test tones and the music. ie Ltf goes to L, Rtf to R, Ltr to Lb, Rtr to Rb which is what I expect to happen.

When I've tried on other discs switching between straight True HD and Atmos I can't hear any difference. I absolutely can on DSOTM in many tracks, but the alarm clocks and the cash register drawers make the issues obvious.

Maybe a fortunate mistake for my understanding. I was not aware of the prior discussions, and your discussion explains a lot.

I've regenerated with MakeMKV the Pink Floyd Animals (probably the same as DSOTM) Atmos test videos, both voice and pink noise versions, so that there is only a single TrueHD audio track, which can be verified with MediaInfo. This eliminates any chance that somehow one of the secondary audio tracks was being used by my Oppo (e.g., the Dolby Digital or the 5.1 tracks). The audio in my tests resides solely in the single 7.1 TrueHD Atmos track.

I've also converted those TrueHD files with the Dolby Reference Player with the assistance of MMH (thanks as always to HomerJAU) to 12-channel interleaved WAV files, then re-encoded them with the Dolby Media Encoder to TrueHD Atmos, again with the assistance of MMH. I added back the video that was previously demuxed from the original MKV and also added the chapters back in. I verified with Audacity that the 12-channel interleaved WAV files generated by the DRP were as expected, with sound bursts in one channel at a time, progressing over time through the channels.

Both sets of files are available here: https://we.tl/t-RKlT2pClpK

Playing these as described before (Oppo 203 configured for Bitstream or LPCM via HDMI to a Smyth Realiser A16) I get, no surprise, different results between the two file sets. The original Animals file maps in 7.1 and 5.1 playback the extra channels (Ltf, Rtf, Ltr, Rtr, Lb, Rb) as described in my first post to a combination of channels. The new versions of the TrueHD files played on 7.1 and 5.1 show none of this channel mixing, simply Ltf->L, Rtf->R, etc., with Lb->Lss and Rb->Rss on the 5.1.

All of which indicates to me that the 5.1 and 7.1 downmixes contained within an Atmos TrueHD file are at the discretion of the engineer who creates them. In the Dolby Media Encoder, the 7.1, 5.1, and 2.0 automatically generated downmixes can all be optionally overriden via a set of individual channel files, so manipulating them is easy, such as to get the funky Pink Floyd versions. MMH generates a set of dummy master Atmos files as described in https://www.quadraphonicquad.com/fo...mos-decoder-beta-discussion.33488/post-746309, basically setting the 4 overhead speakers in 7.1.4 to fixed positions. I did not override the DME (actually the executable is dee.exe so you'll see MMH discussions refer to this as DEE) 7.1 or 5.1 default downmix generation.

 

[kfbkfb]

I think it would be best if the Atmos -> DD 5.1 downmix used the defaults all the time (same in concept as the stereo -> mono downmix: always L+R).

(just do a quick listen to the DD 5.1 downmix and maybe modify the Atmos mix a little if the downmix seems to be noticeably missing some of the music)


Kirk Bayne

 

[SeeMoreDigital]

Dolby have been offering their own speaker mapping test files for years. Starting with (lossy) 5.1 Dolby Digital.

There should be some links somewhere...

Hopefully these links to my OneDrive work: -
Dolby Digital Plus Atmos [7.1.4].zip
DolbyTrueHD Atmos [7.1.4].zip