Apple tv4 7.1 surround not workin

Jon Walker wrote:

Okay. However, if this is true, then the TV3 and TV2 devices are also not passing through the AC3 bitstream since my TV2, TV3, and TV4 all play the same H.264/AC3 source content in the same way

Perhaps your AVR is misleading you, it seems some report/display the surround mode rather than the input signal just as my AVR foolishly reports MPCM as analog.

If I watch movie X with an AC3 soundtrack on my ATV3 my AVR (Denon 4311) reports Dolby Digital input (3/2/.1). If I watch the same movie on my ATV4 my AVR reports multi-channel PCM input (3/4/.1).

No matter what configuration or source I've used so far on the ATV4 I always get MPCM. The number of channels reported is a product of the ATV4 Audio mode and the source. The ATV4 does let me select between AAC and AC3 pass-through sound tracks but the result is the same MPCM.

I've speculated over on AVS that Apple has decided to go old-school and do the decoding in the ATV4 since they know they can send 8 PCM channels over HDMI while they can only speculate if your AVR can decode DD+. In this case they means the staff at Apple (the ATV4 itself should be able to tell if you can decode EAC3). The problem my speculation is the nature of EAC3 chips. If they are using EAC3 as a transport and decoding it in the box then they should be able to bitstream AC3 and EAC3.

It could be an oversight but it might also be a known (to Apple) issue in one of the target markets for the ATV4. Or it could be much simpler to set up the EAC3 core to always decode. Or they might have a special license with Dolby and they're not using an off-the-shelf decoder. Or lots of other things that Apple doesn't talk about.

No, Jon, you are correct; Compressor currently only has support for 5.1 channel output.

@all My working hypothesis is that the random, none-sensical symptoms we are all experiencing with surround playback is a result of the Apple TV 4 corrupting the Dolby Digital 5.1 data stream. I have been working hard to get this resolved with Apple support and your forwarding your symptoms and set-ups to them via feedback or bug reporting would be extremely helpful in getting these issues resolved!

Jeff P., Author, Surround Speaker Check app for tvOS

PS. I'm fairly certain that Apple TV 4 is not performing any of the actual surround decoding. More likely (as per my theory) is that a partially corrupted data stream is false triggering AV receiver flags such as channel count and compression modes, etc... Additionally, decoding in the ATV unit would not be practical unless the ATV was informed by the AV receiver as to the user's individual surround configuration; i.e., has center speaker? bass management, speaker configuration, etc.. (For example, if the user has no center channel speaker, the Apple TV would not know to down mix the center channel info into the L R signal UNLESS there was some way for the AV unit to send that configuration info upstream. AFAIK, there is no such protocol.)

"Additionally, decoding in the ATV unit would not be practical unless the ATV was informed by the AV receiver as to the user's individual surround configuration; i.e., has center speaker? bass management, speaker configuration, etc.. (For example, if the user has no center channel speaker, the Apple TV would not know to down mix the center channel info into the L R signal UNLESS there was some way for the AV unit to send that configuration info upstream. AFAIK, there is no such protocol.)"

This is an excellent point but given Apple's seemingly lack of understanding (or care) when it comes to HT/Surround codec tech it wouldn't surprise me.

I did the phone call to Apple support and went through the whole process of documenting my system and such. They said they will get back to me in about a week.

As it appears that anyone with a 7.1 setup is likely having this issue whether they know it or not, lets get the word out to document it with Apple.

I was very excited about the ATV being able to make use of my 7.1 system so this is a big letdown for me.

To help ease the pain, I blasted the Mad Max Fury Road blu-ray (which is an Atmos recording with True-HD 7.1 core) last night - first time I've watched it since the theater - what an great surround soundtrack! All those crazy war drum beats throughout seriously pump the sub! The separation and locational sound was phenomenal! OK, sorry to get off topic....:)

Here is another good summary of the issue someone is having on and AV site...it cuts to the chase (and also backs up what I thought I recall the old ATV was doing - just passing the bitstream):

"Apple need to fix the audio output options via an update. It clearly is not functioning as intended.

In AUTO mode, PCM 7.1 is being output to AV receivers even when the incoming signal is only 5.1. The rear speakers are silent. And because the signal is flagged as 7.1, you cannot perform AV receiver post-processing like ProLogic IIx to get your rear speakers to work on the 5.1 incoming signal.

Even better, Apple should allow the bitstream to simply pass through to your AV receiver, ie Dolby Digital 5.1 or Dolby Digital Plus 7.1, instead of decoding it to PCM 7.1. That way, Dolby Atmos encoded content could get to your AV receiver. You need to bitstream for Atmos to work.

If you force the audio output to Dolby Surround, then EVERYTHING is transcoded to Dolby Digital AC-3 5.1, even your iTunes music, which may be Apple Lossless or AAC. An unnecessary transcode, and only your front left/right speakers will be active, all the remaining 5.1 channels silent. This is not the way the audio output should work. It appears this setting may even transcode Dolby Digital audio at lower bitrates (ie 384 or 448 kb/s) to 640 kb/s, as evidenced by the info on my AV receiver. That is totally unnecessary, and is compromising audio quality.

AUTO should simply bitstream Dolby Digital audio (And DD+) to your AV receiver, and drop back to PCM 2.0 when only stereo audio is detected in the source (like AAC), just like earlier Apple TV generations."

Thanks for the kind words, Jon. Much appreciated.

The only thing I might recommend would be to look into changing the Test/Sample file settings to automatically select the DD5.1 audio track so it will be compatible with all OS, IOS, and tvOS players rather than allowing the TV4 to default to the stereo audio track as it currently does.

Unfortunately, it is up to the OS to detect the AC-3 (or EC-3) track and substitute for the AAC stereo track whenever possible. AFAIK, there is no way for media producers to "force a default" on our end, so we're at Apple's mercy to provide a quick and reliable update to solve the problem... The Apple TV 2 and 3 models were pretty rock solid on delivery AC-3, so I'm confident they'll get there. How soon, though, likely depends on the amount of user feedback they receive regarding the issue.

I look forward to a final solution to this issue even if I don't use such content myself and hope/assume you will then be updating your app to include a 7.1 audio test routines for the TV4.

Yes, that would be fun! Perhaps after the dust settles a bit... 😉

Jpdev001 wrote:

My working hypothesis is that the random, none-sensical symptoms we are all experiencing with surround playback is a result of the Apple TV 4 corrupting the Dolby Digital 5.1 data stream.

I can believe this. The Dolby Surround output from the ATV4 is not identical per my AVR as the AC3 stream from the ATV3 (or any other device). It could be a glitch in the AVR.

UNLESS there was some way for the AV unit to send that configuration info upstream. AFAIK, there is no such protocol.)

I interpret this part of the HDMI spec:

as describing such a protocol.

Jon Walker wrote:

I had assumed that AC3 and DD+ 7.1 would be passed through to the AVR for decoding and all other supported formats would be mapped to a 7.1 PCM HDMI connection with the AVR. Have no experience with E-C3 so I downloaded a WAV 8-channel sample file and tried to transcode it using Compressor. However, compressor would only allow a max 5.1 channelization.

E-AC-3 is a superset of AC-3. You can encode 1-15 channels. Given an E-AC-3 object how would you get it into the ATV4? Or is there an app for that?🙂

...Sinks supporting multi-channel L-PCM or multi-channel One Bit Audio shall include this Data Block.

Ah, nice find, bodosom! If Apple is doing this, I wonder what is the benefit is to having the Apple TV decoding the signal? Perhaps to one day implement a non-Dolby solution, i.e.: high-def multi-channel AAC?

BTW, I did set my ATV 4 on "Dolby Digital" and played some iTunes 2.0 music this morning. The AV receiver did light up the surround speaker icons, but of course I did not hear anything whatsoever come out of the rear speakers.

meegwell wrote:

"Additionally, decoding in the ATV unit would not be practical"

This is an excellent point but given Apple's seemingly lack of understanding (or care) when it comes to HT/Surround codec tech it wouldn't surprise me.

My naughty AVR did lead me somewhat astray but I'm completely confident that with Surround set to Auto an AC3 stream is (correctly) converted to (7.1) multi-channel PCM. That operation does require decoding AC3.

Jpdev001 wrote:

I wonder what is the benefit is to having the Apple TV decoding the signal?

If they have a strategy of consistently moving to more efficient codecs (e.g. the regular increase in Profile levels) then they might want to go 100% E-AC-3. They're obviously willing to ignore the S/PDIF hold-outs but they might not be willing to require an E-AC-3 decoder in every TV/AVR. That does raise the question of why they don't just use the "free" AC3 converter they have if you don't handshake on E-AC-3.

Apple is inscrutable but I don't think they're stupid.

Having browsed through this thread I understand that I have exactly the same problem with audio out set to Auto. My home cinema receiver displays 7 channel PCM input, but no Dolby 7.1. I don't quite follow the discussions above, but would you agree that changing the setting to Dolby surround at least sends the correct Dolby Digital 5.1 signal to the receiver?

Roggamannen wrote:

Having browsed through this thread I understand that I have exactly the same problem with audio out set to Auto. My home cinema receiver displays 7 channel PCM input, but no Dolby 7.1. I don't quite follow the discussions above, but would you agree that changing the setting to Dolby surround at least sends the correct Dolby Digital 5.1 signal to the receiver?

In my experience dealing with this problem over the past week, I would agree with this. If what you want is your HT to play proper DD5.1 movies on your 5.1 system, imo use the Dolby Surround setting. I assume you see your AVR giving the standard DD 5.1 indication you are used to.

A majority of my rips are done with a 5.1 AAC track and a 5.1 DD track. With the ATV4 set to "Auto", the 5.1 AAC is arriving at my receiver as 2.0 stereo wrapped in 7.1 PCM.

So, the ATV4 seems unable to properly decode 5.1 AAC. (The ATV3 couldn't, either). It seems like it should, though, given its ability to output multichannel PCM. For what it's worth, my Sony Blu-ray player does exactly that - decodes 5.1 AAC and outputs 5.1 PCM.

Discoslap wrote:

Have you tried Terminator Genysi, also you should be getting dolby digital PLUS when playing 5.1 content so it doesnt have to be a 7.1 movie.

The new apple TV should be playing 5.1 dolby digital PLUS which is a higher res codec then just plain dolby digital.

Most Netflix movies are Dolby Digital Plus. It won't work regardless as we will have to wait for a firmware update.

I already returned my 2nd unit as Apple suggested i buy another one just in case it was device specific. Well I guess I have to run around trouble shooting when it just Apples crappy streaming device. I have been waiting for this thing just for the Dolby Digital PLUS codec and what a waste.

Any AV person here understands this, the 5.1 content can be matrixed to 7.1 and still be in Dolby Digital Plus so instead of searching for 7.1 just keep an eye out for the PLUS symbol on your receiver that you will never GET!

I am solely interested in getting DD+ 7.1 to function, but I understand and agree with what you are saying. I have no problems with DD5.1 and I dont care about DD+5.1 (which as you say is not working for me either). I've been in this game a while - head over to avsforum and look up my home theater build from many years ago - same user name.

Anyway, I am interested in files I can confirm are properly E-AC3 encoded, which I cant do with Netflix. I will need to buy a terrible movie to test Terminator Genysis via MediaInfo or some other tool and I dont want to do that.