Questions about multi channel AAC
#1
Hi everyone,
I have a lot of questions regarding hardware for playback. In order to keep things simple, I'll ask one question at a time.

I have a MiBox running Kodi. Things work as well as can be expected.
I've noticed that a lot of what I'm download has AAC audio. I've set things up so it converts it to DD. This is fine up to 5.1, but 7.1 AAC will only get encoded as 5.1 DD.
I'm not sure when AAC became popular, but my question is, is there any way to stream 7.1 AAC properly?
I'm assuming my AVR (Onkyo) won't accept multi channel AAC, this is why it gets converted to DD?
Is there any way to converting it to 7.1 DD?
Why does 7.1 AAC exist? In what situation can you play it 7.1?

Thanks

Yung
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#2
Don't try and pass it through, there is no AMP that anyone has ever found that deals with AAC audio directly.

If it is being converted to DD it is because that is how you have Kodi set up.

Best you just have it converted to multichannel PCM.
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#3
(2018-04-10, 06:26)nickr Wrote: Don't try and pass it through, there is no AMP that anyone has ever found that deals with AAC audio directly.
That's what I thought. So why does AAC exsist? And why is it so popular?
(2018-04-10, 06:26)nickr Wrote: If it is being converted to DD it is because that is how you have Kodi set up.
Yes, I have set it up this way. However it only does 5.1 DD. When it's 7.1 AAC, it still only outputs 5.1 DD. Can this be changed to do 7.1?
(2018-04-10, 06:26)nickr Wrote: Best you just have it converted to multichannel PCM.
How can this be done?
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#4
(2018-04-10, 07:10)puunda Wrote:
(2018-04-10, 06:26)nickr Wrote: Don't try and pass it through, there is no AMP that anyone has ever found that deals with AAC audio directly.
That's what I thought. So why does AAC exsist? And why is it so popular?
Heaven only knows
Quote:
(2018-04-10, 06:26)nickr Wrote: If it is being converted to DD it is because that is how you have Kodi set up.
Yes, I have set it up this way. However it only does 5.1 DD. When it's 7.1 AAC, it still only outputs 5.1 DD. Can this be changed to do 7.1?
DD is a maximum of 5.1
Quote:
(2018-04-10, 06:26)nickr Wrote: Best you just have it converted to multichannel PCM.
How can this be done? 
Turn passthrough and conversion to DD off, set speakers at 7.1
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#5
(2018-04-10, 06:19)puunda Wrote: Hi everyone,
I've noticed that a lot of what I'm download has AAC audio. I've set things up so it converts it to DD. This is fine up to 5.1, but 7.1 AAC will only get encoded as 5.1 DD.
You are transcoding multichannel AAC to DD. DD is limited to 5.1 max, so that is the best you can do with a DD transcode.

If the Mi box supports PCM multichannel output you would be better off setting your channel output to 7.1 and disabling DD transcode. This will get your Mi box to decode the AAC 7.1 to PCM 7.1 and output it as PCM multichannel 7.1 over HDMI.

The same is also true for FLAC multichannel content
Quote:I'm not sure when AAC became popular, but my question is, is there any way to stream 7.1 AAC properly?
AAC (like FLAC) is a popular file-based codec, but has never been an optical disc standard AFAIK. The Consumer electronics industry who standardise HDMI standards and Home Cinema Amp manufacturers are still geared up to supporting optical disk players for bit streaming, and these platforms define the codecs that they support. (DD, DTS, DD+, Dolby True HD, DTS HD MA/HRA, DD + with Atmos, Dolby True HD with Atmos, DTS:x)

A very small number of amps DID support WMA bit streaming. No amp AFAIK has ever supported AAC bitstreaming and I don't think it is standardised for HDMI or SPDIF carriage. (For a while, in the early days, there was a confusion option to enable AAC bitstreaming in XBMC - may have been pre-Kodi - but it was non-functional, as it couldn't ever be functional!)
Quote:I'm assuming my AVR (Onkyo) won't accept multi channel AAC, this is why it gets converted to DD?
No amp accepts AAC over HDMI (or SPDIF) AFAIK

It gets converted to DD because you probably have enable transcode to DD enabled in your Kodi audio settings?  if you didn't it would be decoded to PCM.
Quote:Is there any way to converting it to 7.1 DD?

No - because DD7.1 doesn't exist. DD is limited to 5.1 (possibly a niche 6.1 with some matrix surround extensions - or was that only DTS EX ?)
Quote:Why does 7.1 AAC exist? In what situation can you play it 7.1?
On any amp with a multichannel PCM input  - any amp that supports HD Audio will almost certainly support 5.1/7.1 PCM output.

AIUI AAC is a more modern codec, so may well deliver higher audio quality at lower bitrates than Dolby Digital.  AAC 5.1 is used for broadcast TV in the UK because Dolby Digital didn't support an audio description receiver-mix solution in bandwidth efficient manner when we introduced OTA HDTV in 2009, and TVs can't receiver mix two different codecs cost effectively (or that was the reason given)

It's used for other platforms because it doesn't require a Dolby licence. This is really important for devices like mobile phones, tablets etc. I know mobiles don't output 5.1 - but staying with a single codec does make sense.  AAC stereo is a common codec for streaming and file playback, so sticking with AAC for multichannel makes sense commercially AIUI.
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#6
From your answers it seems like there is a way to get AAC 7.1 or 5.1 to play as 5.1 or 7.1 PCM to the the amp. As long as there is a way to play it, then it makes sense to me.
Thanks for the replies. This has clarified things for me ... at least for AAC audio anyway
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#7
(2018-04-16, 05:08)puunda Wrote: From your answers it seems like there is a way to get AAC 7.1 or 5.1 to play as 5.1 or 7.1 PCM to the the amp. As long as there is a way to play it, then it makes sense to me.
Thanks for the replies. This has clarified things for me ... at least for AAC audio anyway
The MiBox doesn't support mulichannel LPCM output. You will have to transcode AAC 5.1 to Dolby Digital 5.1.
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#8
(2018-04-10, 12:04)noggin Wrote: No amp accepts AAC over HDMI (or SPDIF) AFAIK
Some of the old Pioneer AVRs had support for  multichannel AAC-LC & HE-AAC bitstreaming over HDMI.
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#9
(2018-04-16, 20:28)wesk05 Wrote:
(2018-04-10, 12:04)noggin Wrote: No amp accepts AAC over HDMI (or SPDIF) AFAIK
Some of the old Pioneer AVRs had support for  multichannel AAC-LC & HE-AAC bitstreaming over HDMI. 
Wow - so there WERE some.
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#10
Hmmm?  Unless I'm mistaken, using various players, I have AAC (LC) 8 channel PCM multi channel via HDMI 2.0 working and my receiver is a run of the mill Denon S720W?  Wasapi 7.1 and passthrough settings.
HOW TO - Kodi 2D - 3D - UHD (4k) HDR Guide Internal & External Players
W10/1903 MPC-BE\HC PDVD19 DVDFab3&5 KODI 19 PotPlayer 960-4GB/RGB 4:4:4/Desktop=60Hz/Video=Matched Refresh rates 8bit/65JS8500 UHD HDR 3D
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#11
(2018-04-17, 02:30)brazen1 Wrote: Hmmm?  Unless I'm mistaken, using various players, I have AAC (LC) 8 channel PCM multi channel via HDMI 2.0 working and my receiver is a run of the mill Denon S720W?  Wasapi 7.1 and passthrough settings.
 The discussion was about AAC being decoded by the AVR via HDMI passthrough. It has been in the standards since HDMI 1.3 at least, but very few AVRs actually support it. I am not aware of any AVR made in the last decade or so that supports AAC via HDMI passthrough. There is a renewed interest in AAC passthrough with the upcoming 8K Super Hi-Vision with 22.2 surround sound (Olympics 2020).
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#12
Oh.  I was replying with the OP in mind.  I know nothing about a MiBox but since he asked "In what situation can you play it 7.1?", I thought I'd confirm at least one situation, with what, and how.  I took interest because recently I realized my rare AAC (LC) 8 channel rips were only decoding stereo. 

I installed FFMpeg and used it with command prompt codes to convert my AAC (LC) 8 channel rips to AC3 5.1 so I could decode multichannel even if it was reduced.  I then happened upon a setting in KODI I was not familiar with and stumbled upon. 

I usually set my KODI speaker selection to match my AVR - 7.1.  Then I changed it to stereo which revealed a hidden setting to encode AAC to AC3 on the fly producing DD multi channel limited to 5.1 of course.  This meant no need to convert AAC to AC3. 

To my amazement, I reverted back to my Windows KODI v.17.6 - 7.1 speaker setting, and AAC (LC) 8 channel now decodes as PCM 7.1 multi channel (all 8) and no longer stereo.  I may have changed another setting(s) but I don't recall?  So, to the OP, this is my extended answer relationship using KODI and other player results with AAC (LC) 8 channel playback.  I do not share your device, a MiBox.  This is simply a Windows 10 HTPC through a video card and nothing special about my software or hardware.
HOW TO - Kodi 2D - 3D - UHD (4k) HDR Guide Internal & External Players
W10/1903 MPC-BE\HC PDVD19 DVDFab3&5 KODI 19 PotPlayer 960-4GB/RGB 4:4:4/Desktop=60Hz/Video=Matched Refresh rates 8bit/65JS8500 UHD HDR 3D
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#13
(2018-04-17, 03:45)wesk05 Wrote:
(2018-04-17, 02:30)brazen1 Wrote: Hmmm?  Unless I'm mistaken, using various players, I have AAC (LC) 8 channel PCM multi channel via HDMI 2.0 working and my receiver is a run of the mill Denon S720W?  Wasapi 7.1 and passthrough settings.
 The discussion was about AAC being decoded by the AVR via HDMI passthrough. It has been in the standards since HDMI 1.3 at least, but very few AVRs actually support it. I am not aware of any AVR made in the last decade or so that supports AAC via HDMI passthrough. There is a renewed interest in AAC passthrough with the upcoming 8K Super Hi-Vision with 22.2 surround sound (Olympics 2020). 
  
Yep - I guess passing 24 PCM uncompressed channels vs 24 AAC compressed channels is a driver to save some HDI bandwidth.

I heard some 22.2 stuff at various Super HiVision Demos c.2010-2012. It was very impressive - though the mic array I saw used to capture it in one situation was insane! The London 2012 Olympic Opening Ceremony looked fascinating in 8K.
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#14
I recently started another thread here about EAC3 7.1 DD+ audio.

I feel like this would be an answer to many issues if it were better supported.

Dolby Digital Plus can handle 7.1 channels easily and almost all AVR’s support it. It’s supported my many media players and Apple TV, etc.

I’ve done some extensive testing over the years and it’s pretty amazing with the same compression benefits as AAC, with hardware compatibility and easy pass-thru as bitstream when your media player can’t decode all the channels. Since EAC3 has an AC3 core is always going to give you a downmix of 5.1 in the worse case.

Kodi currently will play DD+ as PCM or pass the bitstream to the receiver. But sadly if you give Kodi a 7.1 EAC3/DD+ file, it only sees it as 5.1 for PCM purposes, and while it will pass the bitstream to a AVR, it doesn’t do it poperly when there are more than 5.1 channels causing the receiver to show errors and not play.

Oddly good old Windows Media Player in windows can do this perfectly with PCM or the 7.1 EAC3 bitstream. But who wants to use that!
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#15
(2018-04-16, 20:26)wesk05 Wrote: The MiBox doesn't support mulichannel LPCM output. You will have to transcode AAC 5.1 to Dolby Digital 5.1.

This explains a lot. OK, thanks for that info.
It seems it's very difficult to get the perfect media player ... but the quest continues
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