Apple tv4 7.1 surround not workin

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.

I am curious as to why you think it more likely that my AC3 audio track for my movie which output via the HDMI connection from my TV4 in the "Dolby Surround" mode is NOT being received as AC3—even though the AVR confirms the HDMI connection, automatically switches to the ""DD Digital" decoder, correctly identifies each active channel, and each active channel plays independent audio content through its corresponding speaker which is easily confirmed aurally by the user.

I readily admit that playing an AAC audio track using the same settings does create some anomalies in that the AC3 5.1 HDMI connection thus created is only mapped with audio to the Front Left and Front Right channels. Unlike an AC3 stereo encoded track which only displays its active channels on the AVR, a "forced" AAC to AC3 connection unconditionally displays as DD5.1 audio but can easily be identified as being a "forced" AC3 connection since the AVR will never display any LFE activity and the user can aurally confirm that the center and rear channels are empty. I assume this may be what you are seeing.

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).

That is what I get if I try to play any AC3 track on the TV4 using the "Auto" mode—i.e., the TV4 connects with the AVR using a "forced" 7.1 PCM HDMI connection.

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.

AC3 "passthrough" is automatic on my system when I source an AC3 track in the TV4 "Dolby Surround" mode. (Am referring to real AC3 encodes here and not DD+ 7.1 audio tracks.)

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.

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. Not sure if I need an update or if this is the max limit for the app or my workflow was incorrect. Will have to look into this further later.

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."

and to make things easier, please submit feedback on how the 7.1 does not work in ATV4:

http://www.apple.com/feedback/appletv.html

Sorry for the delay in responding. Was up until 5 AM and had a medical appointment first thing this AM.

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

Thanks for providing this information. It undoubtedly saved me several hours of fruitless labor.

@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!

Agree this would be a likely scenario for the "random, non-sensical" pseudo-AC3 connection anomalies but I don't use a "forced" workflow to play my content. In fact, I suspect the use of a forced or pseudo-AC3 workflow by not resetting the default audio track of each newly opened file is what is causing the "corruption" issue for a majority of DD5.1 users since I seriously doubt Apple has actually integrated an AC3 encoder into the TV4.

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

Thanks for the reference. I downloaded the app since it was free and its test results mirror the DD5.1 test results of my own DD5.1 content. I.e., failure to reset source track selection results in anomalous pseudo-AC3 playback. With the correct AC3 encoded track selected, your app's graphic display matches my AVR graphic display and individual speaker activity. 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, I'm not sure if the current default track selection algorithm used by the TV4 is a permanent change or not. While the process of changing a few random files is simple, it is not a project I would start arbitrarily for thousands of files before knowing more.

PS. I'm fairly certain that Apple TV 4 is not performing any of the actual surround decoding.

I agree that it is much more likely that Apple's intention is to carry over the same processing routines pioneered for earlier TV devices but updated to support a newly included DD+ 7.1 content option—which seems to have created entirely new "bugs." My only reason for initially posting here was to point out the change in the "Surround Sound > Auto" setting functionality of the TV4 as compared with earlier TV devices. Instead, I became embroiled in an argument questioning whether or not DD5.1 content is stilled supported on the TV4 and whether or not it is actually still being "passed through" for decoding by the AVR. For me the answer to both questions is still a resounding "YES!" Since I'm not involved with either DD+ 7.1 or "pseudo-AC3" workflows, I have nothing more of value to add—something I'm sure will please at least one other contributor to this forum topic.

Again, thanks for your post, Jeff. You are a gentleman. Both the information and app were helpful and appreciated. 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. Best of luck.

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.