7.1 - Side Vs. Rear Speakers

[Sonik Wiz]

I tested the 7.2.4 setup and all was working fine, then re-routed and everything else was firing (LR, C, 4 heights, subs) except the rears and surrounds I ran through the box. Then when I couldn’t get a sound I wired it back and it worked fine. Beats me.

Only other thing is it says it accepts “up to 14 gauge wire” and I’m using 12… I got it in there without issue though, so I can’t imagine that’d be the problem.

It ain't the wire.....

 

[RustyStatic]

It ain't the wire.....

Yeah, that really wouldn’t make sense to me.

Well, I’m not gonna spend any more brain cells on it - I’m a stickler for ripping everything as I get it, and play my 4.0 and 5.1 mixes pretty exclusively through JRiver. I just found out that when I select 7.1 in JRiver, it routes those mixes correctly, with the back surrounds playing the rear channels. So for the small percentage of stuff that I won’t be able to do that with (videos with 5.1 and 5.1/4.0 mixes that are exclusive to Apple Music and don’t have a disc counterpart)… eh, I’ll live, it still sounds awesome.

Thanks for the help and insight, as always!

 

[himey]

There are lot of output in the surround back channels also.

That is your receiver upmixing the sides to the backs, considering that streaming Atmos has a 5.1 bed. It is certainly possible that when it was originally mixed, it was for 7.1 in mind, and the 5.1 is downmixed for the streaming format. So, you could say that your receiver (Atmos decoder) is upmixing the side channels, BACK to the backs.

Edit.
I was wrong about this. See this thread for a nice explanation of how the back and side channels are presented from a 5.1 streaming bed.

 

[sjcorne]

That is your receiver upmixing the sides to the backs, considering that streaming Atmos has a 5.1 bed. It is certainly possible that when it was originally mixed, it was for 7.1 in mind, and the 5.1 is downmixed for the streaming format. So, you could say that your receiver (Atmos decoder) is upmixing the side channels, BACK to the backs.

The undecoded core of streaming Atmos (DD+/JOC) is indeed 5.1, but the full 7.1.4 decode from Apple Music (I don't have Tidal) definitely includes the discrete back channels in addition to the sides. It's easy to test with the Dolby Labs test tones, or just solo sides versus rears on a really discrete mix like Grateful Dead or Tom Petty.

 

[himey]

The undecoded core of streaming Atmos (DD+/JOC) is indeed 5.1, but the full 7.1.4 decode from Apple Music (I don't have Tidal) definitely includes the discrete back channels in addition to the sides. It's easy to test with the Dolby Labs test tones, or just solo sides versus rears on a really discrete mix like Grateful Dead or Tom Petty.

How does that work?

 

[sjcorne]

How does that work?

I don't have the specifics on how the encode/decode process works, but whenever I convert a .MP4, .M4A, or .EC3 file to PCM I get only six channels as you say (the sides & rears are summed). However, If I decode said file with the DRP or just bitstream through my Denon S750 (configured for 7.1 rather than 5.1.2) I get the discrete sides & surround backs. The same goes for Apple Music: if my MacBook Pro is set for 7.1.4 in Audio MIDI Setup, I get all the channels. I can also get true 7.1 from Apple Music on the Apple TV by bitstreaming through the Denon AVR.

Did you think streaming Atmos was limited to 5.1.x? It can go all the way up to 9.1.6, assuming you have the necessary hardware. The only restriction is for legacy (non-Atmos) playback, you get 5.1 whereas Dolby TrueHD would give you 7.1 instead.

 

[himey]

I don't have the specifics on how the encode/decode process works, but whenever I convert a .MP4, .M4A, or .EC3 file to PCM I get only six channels as you say (the sides & rears are summed). However, If I decode said file with the DRP or just bitstream through my Denon S750 (configured for 7.1 rather than 5.1.2) I get the discrete sides & surround backs. The same goes for Apple Music: if my MacBook Pro is set for 7.1.4 in Audio MIDI Setup, I get all the channels. I can also get true 7.1 from Apple Music on the Apple TV by bitstreaming through the Denon AVR.

Did you think streaming Atmos was limited to 5.1.x? It can go all the way up to 9.1.6, assuming you have the necessary hardware. The only restriction is for legacy (non-Atmos) playback, you get 5.1 whereas Dolby TrueHD would give you 7.1 instead.

I really haven't thought about it until now. I have always been a little bit skeptical about Atmos being a first-generation product, and how they want you to add more speakers and trust the process of a tiny chip, rather than outputting truly discreet channels, mixed in the studio.

 

[sjcorne]

I really haven't thought about it until now. I have always been a little bit skeptical about Atmos being a first-generation product, and how they want you to add more speakers and trust the process of a tiny chip, rather than outputting truly discreet channels, mixed in the studio.

"Truly discrete channels" isn't really the right way to look at it, as the use of objects allows the mix to expand beyond even the number of speakers used in the studio it was created in. Steven Wilson uses a 7.1.4 setup, but some guitar parts in his Grateful Dead Atmos mixes appear partially in the wide speakers on a 9.1.x setup because he assigned them to objects positioned somewhere between the front & side channels.

The Dolby Atmos Renderer software used at the mixing stage is the same thing as that 'tiny chip' in our AVRs, allowing the mix to expand and contract based on the # of available speakers in one's setup. I guess I could understand the skepticism around this, but there's really no trickery involved - what you hear from the streaming services on speakers is absolutely the same as what they heard in the studio (albeit with less detail and some artifacts from the low bitrate). Take my word for it, I have the ADM masters for a number of albums to compare directly.

 

[perzon57]

That is your receiver upmixing the sides to the backs, considering that streaming Atmos has a 5.1 bed. It is certainly possible that when it was originally mixed, it was for 7.1 in mind, and the 5.1 is downmixed for the streaming format. So, you could say that your receiver (Atmos decoder) is upmixing the side channels, BACK to the backs.

I'm not sure about that, will check it out tonight.

 

[himey]

I'm not sure about that, will check it out tonight.

Did you read the thread I linked, post #63? It really explains a lot of the differences between Blu-ray Atmos and streaming Atmos, including the additional two bed channels.
It also answers why the top channels sound more lossy than the bed channels which I knew was the case, thanks to @sjcorne.

 

[LuvMyQuad]

This isn't the first time I've read about the side -rear fold down issue. Wouldn't it have been better for the algorithm to split the sides signals between the fronts and rears instead of defaulting all of it to the rears? Maybe that opens even more problems? There could have been a setup option for it tooffer a choice.

 

[sjcorne]

Wouldn't it have been better for the algorithm to split the sides signals between the fronts and rears instead of defaulting all of it to the rears?

It does that if objects are used for the side speakers while mixing instead of a 7.1 bed, but only if you listen through an Atmos-capable receiver. With older gear, the sides go to the back regardless of whether a bed or object was used.

 

[himey]

Here is more info on the subject.

 

[perzon57]

Did you read the thread I linked, post #63? It really explains a lot of the differences between Blu-ray Atmos and streaming Atmos, including the additional two bed channels.
It also answers why the top channels sound more lossy than the bed channels which I knew was the case, thanks to @sjcorne.

No I didn't read it, but I listened to the track again and there are bass and vocals in the surround backs at times that are not in the surrounds.
How can the decoder up mix something from the surrounds to the surround backs that is not present i the surrounds at that time?

 

[himey]

How can the decoder up mix something from the surrounds to the surround backs that is not present i the surrounds at that time?

It is more complicated than simple upmix processing. Read the links in posts #63 and #73.