AppleTV 4 surround sound issue

Of note, movies purchased via iTunes work just fine, this is what Subler shows:

Here's my data points: ATV4 to TV via HDMI, TV to Onkyo 5.1 AVR via digital audio. Worked fine with ATV3. With ATV4's Surround Sound set to Auto or Dolby, 100% of what I play turns on the Dolby section of the AVR. This includes obvious stereo content such as iTunes music and older Hulu and Netflix content. Following a suggestion above, setting ATV4's Surround Sound to Stereo gives me correct two channel output. The wife asks the obvious question: how does she know what should be Dolby and what should be stereo? Yeah, good luck with that. Hoping for a fix from Uncle Tim. Wonder if it is worth calling Apple support?

I also played with Surround Speaker Check, Dolby works as expected.

Mark Hodges wrote:

Here's my data points: ATV4 to TV via HDMI, TV to Onkyo 5.1 AVR via digital audio. Worked fine with ATV3. With ATV4's Surround Sound set to Auto or Dolby, 100% of what I play turns on the Dolby section of the AVR. ... Wonder if it is worth calling Apple support?

If it's exactly as you report either your ATV defective or AVR is reporting the wrong status.

Using content from the Music app or the Computer (iTunes) app (although they are just examples) that is correctly encoded:

• Given Surround:AUTO, 7.1, 5.1 and 2.0 input produce 7.1 PCM with the correct number and placement of channels
• Given Surround:DOLBY, 7.1, 5.1 and 2.0 input produce transcoded 5.1 with correct channels.

It's been suggested that ATV4gen decodes bitstreams to do volume/loudness/dynamic range compression (so called midnight mode) on the resultant PCM streams.

So this is getting so confusing for me now. Somehow Apple always makes things so confusing for people who just want things to work how they are supposed to.

I am thinking about buying the new ATV4. I have a receiver and all I want is that when I play movies (through Plex or some other software) that the ATV just passes my bitstream sound through to my AV receiver without modifying it (ATV will be connected to the AVR which is then connected to my TV). So I just want the ATV not to do anything at all with the sound. If it is DD, DTS, stereo or whatever. I just want the ATV to just pass it through to my receiver and let the receiver do the work.

Is this possible? Seems to me after reading the whole topic that it is not.

I really like the new ATV and the interface with the remote. But if it's not going to do what I want than it's useless. After all Apple should realise I didn't buy my expensive AVR and speakers and had it set up so Apple can play their simulated tracks over it.

With DD 5.1 as streaming source and ATV set to 'surround' your receiver will receive pass-through DD stream.

With DD+ 7.1 your ATV needs to be set to 'auto' and in that case will send an LPCM stream 7.1 to your receiver, so no DD+ stream received in that case.

This (incorrect?) behavior might change in an upcoming ATV software upgrade.

ATV does not support DTS.

Are you using 5.1 or 7.1 speaker setup?

Yes, Apple, please enable DTS and Dolby Digital Plus passthrough!

Right now DD+ is converted to PCM. If the DD+ bitstream carries Dolby Atmos the whole Atmos information gets completely lost.

If the option Settings > Audio and Video > Surround Sound > Dolby Surround is selected everything gets transcoded to Dolby Digital (no Plus) which potentially degrades audio quality because Dolby Digital is a lossy format.

I hope they implement this correctly. It is ridiculous to make a device and try to revolutionize TV and then do this kind of silly stuff.

I mean pass through mean that the original stream is passed through without altering it in any way. Adding an option for true pass through would also solve the problem of DTS, as it would be passed through and processed by the AVR. As far as i know no license is needed to pass through DTS. Additional option can be added to select what formats are not supported by your receiver so that in that case sound can be altered and send by the ATV as is done now.

untill this is solved the ATV is a no go for me.

There is a persistent misunderstanding about "correct" performance. People read the specifications and then interpret them incorrectly and accuse Apple of being ridiculous or inept or incompetent. Apple does not claim or assert that they are doing pass-through. The ATV5,3 running 9.0.1 will encode to AC-3 in Dolby mode. That AC-3 stream is not the original input.

Currently Apple does not do pass through of any bitstream audio. Presumably this is to support volume compression and limiting.

Apple does not have Atmos in the specifications so they don't have to support the bitstream required for it to work.

Apple does not have DTS in the specifications so they don't have to support the bitstream required for it to work.

Apple does have E-AC-3 but that is (currently) admittedly misleading. The ATV5,3 running 9.0.1 will send 8 channels (correctly assigned) but you can't load E-AC-3 into an iTunes server. Of course you can't load TrueHD/MA into iTunes either. The Plex app might help with this in the future.

bodosom, you are correct that Apple doesn't advertise DD(+) pass-through but they also don't advertise DD(+) decoding. I don't know the reason for this since such decoding eats away resources and costs them licensing fees. By the way, they seem to do DD 5.1 pass-through.

Apple doesn't need to "have Atmos in the specifications" as it rides along a normal DD+ stream. No hardware or software enhancement necessary.

Not sure if PLEX will help as the above behavior seems to be related to the capabilities of Core Audio.

HAL9000.2 wrote:

bodosom, you are correct that Apple doesn't advertise DD(+) pass-through but they also don't advertise DD(+) decoding. I don't know the reason for this since such decoding eats away resources and costs them licensing fees. By the way, they seem to do DD 5.1 pass-through.

Apple doesn't need to "have Atmos in the specifications" as it rides along a normal DD+ stream. No hardware or software enhancement necessary.

Not sure if PLEX will help as the above behavior seems to be related to the capabilities of Core Audio.

If your AVR displays dialog normalization you can see that AC-3 is not pass-through. In fact if your AVR is like mine it might hint that it's not a compliant AC-3 bitstream because dialnorm is missing.

Again, Apple provides volume compression and limiting. My understanding is that to do this they have to decode the bitstream. My understanding is also that other CE gear does the same thing and works the same way. I haven't tested it but I assume the ATV3 does something a bit similar since I think it will down-sample AC-3 to PCM 2/.0.

Presumably since they don't assert Atmos but they do assert E-AC-3 you can (perhaps unexpectedly) draw the conclusion that they're doing a decode to PCM. Or you can just look at the PCM output and think "Oh, right, they're doing volume management".

With regard to cost: it's probably inconsequential and simplifies design. Perhaps they've decided that even though 100% of the target market has HDMI and 99% can decode an AC-3 bitstream maybe E-AC-3 is not ubiquitous.

I mentioned Plex in the context of streaming 7.1 E-AC-3 from a local library since the Computer App/iTunes don't currently support that.

So your assumption is that volume management is the reason we can't have unprocessed audio and Atmos? I'd definitely would like to have unprocessed audio, i.e. bitstream pass-through. The option "Reduce Loud Sounds" could trigger this as it's already available in the "Audio and Video" options.

I'd provide feedback to Apple if you'd changes.

I just did send a feedback. May be an idea that more people do this too. It takes less than 5 minutes but if Apple gets more responses at least they will know it matters to the users

If your AVR displays dialog normalization you can see that AC-3 is not pass-through.

Am confused by this statement. If the AVR display of a dial norm message such as this:

or as the complete sequence (idle Stereo PCM message to dial norm message to DD Digital decoding message) is displayed in the video clip at the following URL: http://downloads.walker4.me/Temporary_files/IMG_0024.m4v, then no SPDIF or HDMI device (i.e., any TV, DVD, or BD Player) has ever "passed through" AC3 encoded audio to my receiver since it was initially set up and calibrated. (I.e., I always get a Dial Norm +4 notification when playing an AC3 file/DVD/BD audio track when using a "Dolby" compatible TV mode or DVD/BD device.)

Yes, that statement by bodosom isn't correct as dialnorm is part of the AC-3 specs. It's not an indicator whether an AC-3 stream has been tampered with or not.

Please see https://en.wikipedia.org/wiki/Dialnorm