AppleTV 4 surround sound issue

I can't speak to Apple's choices. They make decisions that disappoint some customers with every product they release. The obvious answers are:

1) tvOS is a work in progress.

2) Apple has produced a product that is, or they think is, sufficient for the target audience.

3) They anticipate apps will be written to take advantage of new opportunities (i.e. defects).

Point 1 suggests some patience. Point 2 suggests cutting your losses and using another device (in general or just for content that doesn't come from Apple). Point 3 suggests unbridled, but not necessarily unfounded, optimism.

😀

Was just about to climb into bed last night when I saw your response. Had to chuckle.

Agree that tvOs is a work in progress but patience seems to just allow Apple to move further and further away from the the target. I.e., under tvOS v9.0 and v9.0.1 the bitstreams (with or without parameters) decoded channels and post-processed them automatically as encoded. Now it doesn't.

As to third parties taking advantage of "new" opportunities, Am waiting to see if Infuse Pro updates their player with E-AC3 passthrough support. (Would use their player on a full time basis if its software were fully integrated with iTunes library management.)

As to the second point, even if Apple is satisfied with the product today, am sure they will come up with some new "improvement" they'll want to add tomorrow—whether or not users want it.

In any case, I now have a new "pet peeve." Thought I might have come up with a workaround for my current AC3 problems—i.e., I tried to get the TV4 to play an H.264/AAC 5.1 file today. File is acceptable to iTunes for management and the TV4 recognized the content as 5.1 multichannel in both the Best Quality and Dolby Digital 5.1 output modes. In fact, it even created the appropriate 5.1 PCM and AC3 bitstream connections with my AVR. Unfortunately, both connections only sent Right and Left channel audio to the receiver. Not sure if recognition of multichannel audio implies that Apple plans to include TV4 decoding of AAC 5.1 audio or not. (I.e., my old G5 can play video files having AAC 5.1 audio via peripheral card having 6 discrete output channels but I don't know if Apple is still exploring such avenues.) In any case, I was disappointed that even the ProLogic II encoded stereo test track sounded better than the 5.1 (stereo) track playback. Main advantage here would be the playback compatibility of a single audio track for playback as stereo or 5.1 multichannel in the 384-448 Kbps data rate range. (Only tested 384 and 448 Kbps data rates thus far for such content but the tracks played equally well on all all devices but only the TV4 recognized the multichannel nature of the source track. Anyone come across any information regarding this subject?

I've been encountering the AAC 5.1 playback bug since 9.0, and actually posted about it here a while back. The interesting thing is, apps like Air Video HD seem to properly decode the AAC bitstream to 5.1 PCM, so the hardware is obviously capable and the APIs are there. It's nothing more than a bug in the "Computers" app (iTunes Home Sharing). Air Video is now my preferred method of playback on the ATV4, though it's not particularly pretty and doesn't support metadata.

Also, it's worth noting that the "Computers" app isn't simply just sending the L/R channels from the AAC 5.1 mix, it's actually downmixing the source 5.1 to stereo, then encapsulating that in a 5.1 PCM stream. Very strange.

I've been filing product feedback regarding this issue since the day I first got my ATV4, and I resubmit every time another tvOS update is released without a fix. But still nothing...

Alright, all. This discussion is way above my pay grade and well over my head. So for this simple guy who has a pretty nice 5.1 setup, which is the best audio option for watching iTunes movies & TV shows and Netflix for me to select? Dolby digital or Best Audio Available? I just want the audio to sound as good as possible.

Thanks.

Use Best Quality (or Auto if you haven't updated to tvOS 9.2).

I've been encountering the AAC 5.1 playback bug since 9.0, and actually posted about it here a while back. The interesting thing is, apps like Air Video HD seem to properly decode the AAC bitstream to 5.1 PCM, so the hardware is obviously capable and the APIs are there. It's nothing more than a bug in the "Computers" app (iTunes Home Sharing).

Thanks very much for responding regarding this TV4 Surround Sound sub-topic. You have undoubtedly saved me days of research and preliminary testing on my own system. Haven't played with AAC 5.1 since updating to iMac I7 which, of course, can't use my old peripheral card. Love the simplicity of creating a single audio track that automatically plays as mono, stereo, or multichannel depending on the device in use, as well as, the reduction in audio bandwidth requirements.

Was in the process of testing HE AAC 5.1 (192Kbps @ 48.0KHz target) file in the Plex server/player software when you posted. Internet articles indicated Plex software is AAC 5.1 playback compatible but didn't indicate if it was being transcoded before serving or being played back natively in the TV4 media player app. Have both the Air Video and Air Video servers up and running for external network access of iTunes managed library content but never thought to test AAC 5.1 content in the TV4 Air Video HD app. (Boy, do I feel abashed and stupid for overlooking this workflow!) Again, thanks for pointing out the obvious.

Like mariotheplumber, I tend to think playback of (in this case, the AAC 5.1) audio via TV4 DD 5.1 output mode sounds better—i.e., the AVR Dolby decoding algorithms seem to provide better "directional steering" of audio content (volume, phase, and time shifts) to produce better "subjective" channel separation with increased impact and a "fuller" sound at lower master volume levels while the PCM mode qualities seem to improve as master volume levels are increased. (Just a personal opinion which others may or may not share depending on system hardware and playback conventions, habits, and/or personal AVR settings.)

In any case, your comments regarding hardware capabilities and API availability (as well as, the currently demonstrated third-party app functionality) leads me to believe there is still hope for Apple to, as you put it, fix this "bug in the 'Computers' app." Especially since MPEG-4 audio and video is Apple's own choice for OS, IOS, and tvOS basic use and I am very excited about it's potential for "universal" use across multiple Apple devices.

Air Video is now my preferred method of playback on the ATV4, though it's not particularly pretty and doesn't support metadata;

Yes, I have to agree that I am not totally satisfied with any third-party player app when it comes to integration with iTunes managed database and would much prefer, generally speaking, to use Apple's own Computer app player if it will support multichannel AAC audio. (Though I have to confess that I was a bit upset by Apple's latest TV Show playlist ordering inconsistencies in the tvOS v9.2 update.) Would point out, however, that the Air Video HD player does appear to work better than than the Plex player based on less than 24 hours use and have yet to try any other Plex server compatible player apps. Specifically, the Plex player tends to "stick" in the "idle" audio mode for whatever TV4 output mode you are using if you switch modes while playing an AAC 5.1 file. (I.e., the player appears to only test the audio format when a file first opens for playback—making the user exit playback after changing the the TV4 output mode in order to force the player app to resample and reset correct output for the device,) On the other hand, the Air Video HD player does not have this problem as it seems to check for such changes in output each time playback is paused and restarted. In addition, the Plex server has to be manually told to update the media file database for a target library folder while the Air Video HD Server does this automatically when the player app is opened on the TV4. Admittedly these are trivial but, for me, somewhat annoying issues.

Also, it's worth noting that the "Computers" app isn't simply just sending the L/R channels from the AAC 5.1 mix, it's actually downmixing the source 5.1 to stereo, then encapsulating that in a 5.1 PCM stream. Very strange.

This may actually the the key issue here. My understanding is that the AAC downmix routine is only supposed to be called by the OS, IOS, or tvOS player when required to maintain compatibility with device playback hardware, software, and/or output mode settings/limitations. It is indeed strange that third-party software purveyors seem to be out "Apple-ing" Apple here,

I've been filing product feedback regarding this issue since the day I first got my ATV4, and I resubmit every time another tvOS update is released without a fix. But still nothing...

Suspect the number of users employing AAC 5.1 and/or HE AAC 5.1 audio for their video library on a regular basis may be relatively few. You may wish to open an AAC multichannel specific discussion if you have not already done so. I would be interested in comparing notes regarding best target settings and general support by the various applications currently available—especially those operating under tvOS. Am currently contemplating a test switch to AAC multichannel beginning with the release of the latest Star Wars film and The Expanse TV show next week and will likely begin filing feedback and/or "bug" reports as soon as I'm able to gain enough info regarding the subject. Again, I had no idea that anyone was using AAC multichannel for their media library and am very enthusiastic about its potential as more Mac friendly, general purpose, universal audio codec for users not requiring ultra-high quality audio formats.

Thanks, all. I've been set to DD 5.1 since the update but I will go back to Best Audio Quality to see if I can hear any differences.

BTW, this has been a most educating thread, of what I can understand anyway!

If you have a 7.1 System, setting it back to BAQ will render your rear two speakers dead. Most AV Processors will leave PCM 5.1 stream alone and send it channel to channel. Great if you have 5.1. Terrible if you have 7.1 System.

SuperSizeIt wrote:

If you have a 7.1 System, setting it back to BAQ will render your rear two speakers dead.

The post we responded to was very specifically about a 5.1 system -- but using Best Quality PCM output doesn't "render your rear two speakers dead", likewise PCM 2/0 doesn't render your 1/2/.1 speakers "dead". If you play an iTunes movie with a 7.1 soundtrack you get expected content.

Yes it does. If you play Movies with 5.1 soundtrack, your AV cannot process PCM to use it's own method of using 7.1 PLX II or DTS 6. Apple has stopped sending AC3 bitstream natively so users can no longer use AVR systems to do it's own method of Surround Processing. You are forced to use AT4 inferior methods of processing sound. ATV 3 allowed users to but ATV 4 doesn't. Period.

I know from my AVR it needs to be a DD signal being received in order for it to do any post processing to correctly activate the clever stuff to split the surround sound signals and 'spread' them across the rear speakers. I don't believe it can do it with pure PCM 5.1. I don't know if this is universal or just a limitation of my Pioneer AVR but I think it has to receive the DD unmolested in order to do it effectively.

You mileage may vary. Have to admit i've left things on PCM for the most part, removed my rears and gone back to 5.1 only.

SuperSizeIt wrote:

Yes it does.

No it doesn't. You're misleading people. Currently in BQ mode:

1. Given an eight channel source the ATV 4gen sends eight PCM channels with the content as mixed.
2. Given a six channel source the ATV 4gen sends eight PCM channels with the rear surround channels empty as they were mixed.
3. Given a two channel source it sends eight PCM channels with the sw, rear, center and surround channels empty as they were mixed.

People that need an AC-3 bitstream to create fake channels should use the AC-3 output mode.

People that need two channel PCM to create fake channels should use the Stereo output mode.

There some cases where things may not work as Apple planned but eight in/eight out, six in/six out and two in/two out work just fine.

If you had said "Six channels carried in an eight channel PCM stream may not up mix to more than six channels" you would have been correct but you said something very different.

GOod lord. Apple apologist are ridiculous here. Explain then why ATV 3 send it perfectly for AVR processing to DD PLX II ir DTS 6 and more while ATV4 can't. Explain why ATV 2 and 3 could provide AC3 stream and ATV 4 can't. That's the problem that you keep skirting around and making up BS. give it up. People understand the problem yet Apple apologist make up excuses. lol

If people understand the problem why are you asking for an explanation, surely you are 'people'

SuperSizeIt wrote:

Explain why ATV 2 and 3 could provide AC3 stream and ATV 4 can't.

As has been said many, many times including the post you just replied to the ATV 4gen can send an AC-3 bitstream. Either as an override using the Dolby Digital setting or via other apps like Infuse. Perhaps you should read more of this thread. What's going on has been well documented and dissected here. Apple provides a complete explanation here: About surround sound settings on your Apple TV (4th generation) - Apple Support

Just avoiding the differences between versions for the moment. The article would suggest that if you want the AVR to 'break out' the 2 additional rear channels, then having the ATV4 re-encode to DD 5.1 would be the way to go. Correct ?

I have files which have AAC 5.1 and AC-3 5.1 streams encoded in them, and BQ setting throws PCM 5.1 to my AVR