AppleTV 4 surround sound issue

Most sources are 5.1, but when fed from ATV3, the AV receiver can then apply PLXII, EX or DTS 7.1 sound. So all speakers are active.

With ATV4 Auto, the receiver cannot process the sound to output PLX II, EX or DTS 7.1. It's stuck on 5.1 only, thus leaving the other two rear speakers silent. The self powered subs are fine since they are split into two from the sub out of the receiver.

Most sources are 5.1, but when fed from ATV3, the AV receiver can then apply PLXII, EX or DTS 7.1 sound. So all speakers are active... With ATV4 Auto, the receiver cannot process the sound to output PLX II, EX or DTS 7.1. It's stuck on 5.1 only, thus leaving the other two rear speakers silent. The self powered subs are fine since they are split into two from the sub out of the receiver.

Mmmm.... Sounds like this is related to or an extension of the 2.1 ("active" matrix 3- and 4-channel audio) problems I've been complaining about. Since the TV4 outputs these older audio formats in what I call a "pseudo" multichannel bitstream, it automatically disables any automatic Dolby "active" matrix post-processing of audio for any formats so encoded. While I can manually apply passive post-processing enhancements, they aren't the same and force me to "color" the audio with, what is to me, an undesired audio "effect" that must be selected by the user. Like your TV3, the TV4 never had this problem prior to the tvOS v9.1 release that eliminated AC3 bitstream passthrough in the "Dolby Surround" mode. Basically, at this point I have to choose between the better video processing and apps of the TV4 and the better audio processing of the TV3—a bitter choice that Apple should not be forcing users to make in view of the fact that there is so little 7.1 TV4 compatible content available. Of course, this is only my personal opinion and I suspect the vast majority of users out there are like my wife who plays little, if any, attention to whether the audio is mono, multichannel, or anything in between.

Sounds like my Mrs, but it's important not just for audiophiles but for those who want to enjoy the blu ray experience with the convenience of streaming from your iTunes library, which is let's face it, the whole point of the device

Unfortunately lot of my files were, by my oversight, encoded to Dolby Pro Logic II, which one the face of it isn't recognized in auto mode. Maybe I'm wrong as it appears that stereo only is received.

in any case, I'm in the process of obtaining new files and will be encoding them with discrete channels as these appear to come through to my AVR as discrete PCM 5.1

just wish it worked as the ATV3 worked.

Unfortunately lot of my files were, by my oversight, encoded to Dolby Pro Logic II, which one the face of it isn't recognized in auto mode. Maybe I'm wrong as it appears that stereo only is received.

That is because ProLogic II is a "matrix" encoding format that "folds" up to 5 channels of audio (right front, center, left front, right rear, and left rear) and store them as "stereo" (2-channel) audio while ProLogic (Dolby Surround) does the same for up to 4 channels of audio (left, right, center, and mono rear). Since the audio is stored as "stereo" audio, it is compatible with all standard 2-channel devices as is but the component audio content can be filtered, phase-shifted, volume changed, and/or time shifted to "steer" the audio "directionality" of the original multichannel sources. The problem with Apple's current approach is that it disables the ability of the downstream device to automatically recognize and activate the ProLogic decoding which, in turn means the user must either activate such decoding manually when needed (no active indication available) or leave the decoder on at all times (produces unstable output of unencoded audio). On the other hand, if the same audio is passed through to the downstream device in its original AC3 format, the Dolby decoders do recognize the active DDPL/DDPLII encoding and does apply proper decoding and post processing automatically and, as a result, provides an exceptionally stable multichannel "simulation" of the original source audio which is why I keep saying the current workflow just isn't the same or as good as the "passthrough" functionality previously used.

just wish it worked as the ATV3 worked.

Totally agree. Keep posting feedback to this affect—especially after each tvOS update—until Apple realizes how many users have noted and abhor the current degradation in functionality of the TV4 and restores full Dolby support.

Tthat explains it then, why I'm forced to re-encode my files to discrete 5.1 with larger file sizes and the effect bring I get PCM as I'm either encoding using pass through or 5.1 with handbrake

Yamaha RXA-1040 - Left/Right/Center speakers connected

ATV4 set to "AUTO" - receiver displays PCM / Surround Decode... content plays OK

ATV4 set to "Dolby Surround" - receiver displays PCM / Pro Logic... all dialogue is output to Right speaker channel

ATV4 set to "Stereo" - receiver displays PCM and whatever the last decode method used was

Results are same regardless if playback is from iTunes movie / purchased music / Apps (Netflix/BBCiPlayer)

I have to manually switch decode method on the RXA-1040

I'm going to reconnect the ATV3 via optical and compare.

Additionally, I can not get rid of the RXA from appearing under the Airplay menu. It did disappear when I turned on "restrictions", but after sleep on wake up it's back again.

Thanks for this. Appears Apple is still not fixing this. We just want to have the option to output the exact bitstream that is in the original source without conversion or alteration. I would think Dolby would be using for this too since it would enable ATMOS support on the ATV4 for DD+ soundtracks.

Maybe I don't understand the issue here, but after this week's update, I am now able to get the content on ATV 4 to play DD 5.1. The menu gives me the choice between Dolby digital 5.1 and Best Sounding Audio. I am not sure what best sounding audio is, but before I changed it to DD, I was still getting PCM audio.

So my question is, what does Best Sounding Audio include? Does Apple or any of the providers that stream thru ATV 4 broadcast in other than DD 5.1? I thought movies you buy or rent via iTunes to play on ATV 4 were only encoded in DD 5.1.

Thanks for any knowledge.

Gator5000e wrote:

Maybe I don't understand the issue here, but after this week's update, I am now able to get the content on ATV 4 to play DD 5.1.

Apple hasn't changed the capability they just changed AUTO to BEST QUALITY (BQ). There is no functional difference that I see.

BQ should produce PCM output with the channels labeled corresponding to the input bitstream. It does this correctly with 2/0, 3/2/.1 and 3/4/.1 source channels. Previous versions were reported to break some less common layouts like true mono (1/0) which was converted to phantom center (2/0). I don't know if this is still the case.

Naturally many customers would like Apple to simply pass the bitstream through -- untouched -- for decoding in another device (e.g. the AVR). Note that prior to the 9.2 release the bitstream was decoded and then re-encoded in the ATV. I haven't checked to see if that's still the case because it really doesn't matter to me.

Thanks, I think I understand. For my simple setup, AVR with a 5.1 surround system, I now get DD 5.1 sound back according to my AVR. After the 9.2 update, I wasn't getting DD 5.1. My AVR was only showing PCM (via Auto) or Stereo (via Dolby Digital 5.1). Now my AVR shows DD 5.1 if I select DD 5.1 in the sound set up screen.

Would like to hear John Walker's comments after the latest update. At the moment , I've left things as Best Quality and I'm getting PCM 5.1. If I change it to DD I get the AVR to flick to display DD 5.1 Dial Norm +4, so I assume it's getting the DD stream.

However, as PCM is less compressed, as far as I know, than DD, I've left it as Best Quality setting

The DD setting does allow me to apply THX post processing to the DD signal though within the AVR, although I've just checked so does Best Quality on the PCM stream.

i assume I'm right about PCM being less compressed than DD, I'm getting 5.1 with PCM so I'm not losing anything and the soundtrack does sound "fully"

I don't know if everyone's seen this, but there's an interesting article on the Dolby Developer page that sheds some light on this.

Unfortunately, seems to be a "feature", not a bug. It states that:

Apple TV includes a built-in decoder for Dolby Digital Plus and Dolby Digital audio. This means that the Apple TV is able to decode Dolby audio rather than simply pass the compressed bitstream to another device

Decoding the audio inside of the Apple TV enables Apple to support several features such as mixing of other sounds from the system, Siri® voice input, and so on.

And goes further to explain that while the Auto setting will always send PCM audio (stereo, 5.1, or 7.1) to the connected receiver, the Dolby Surround setting is only intended to force the ATV to export a Dolby Digital compressed bitstream for older devices that don't support multichannel PCM.

When this [Dolby Surround] setting is selected, the audio is first decoded (although constrained to 5.1 channels) and mixed with other system sounds, and is then reencoded to the legacy Dolby Digital format just prior to the HDMI output. The connected device (TV, sound bar or AVR) will then receive a Dolby Digital bitstream.

Hence the issue we're all having. Unlike the ATV3, which would simply pass through the existing bitstream for the receiver to decode, the ATV4 is decoding everything, mixing with system sounds (and, per many of us, adding unwanted compression and dynamic range limiting), then RE-encoding it before outputting as a bitstream. It may or may not be factoring the Dialog Normalization into the initial decoding, but the re-encoding certainly sounds quieter and missing dynamic range compared to the original.

So basically, we are stuck with this arguably inferior AC3 bitstream because ATV4 insists on having a way to mix in system sounds. Until Apple decides to offer up a fourth sound option- passthrough- it appears this is the way this is going to stay.

I would suggest in any future messages to Apple, you mention that you as a user would like to see the option to passthrough the existing bitstream restored, even though we're aware that may limit Siri and other functionality that depends on mixing in system sounds (something I don't think anyone wants during movies anyway). Otherwise, it looks like this isn't a simple "oops we forgot to include that", it's another example of Apple saying "we know this is how we've always done it but we do it this way now, get on the bus."

johnnyapollo wrote:

I don't know if everyone's seen this

It was posted earlier to this thread by someone that signed the post Dolby Developer Support.

See page 16

Airsculpture wrote:

I've left things as Best Quality and I'm getting PCM 5.1. If I change it to DD I get the AVR to flick to display DD 5.1 Dial Norm +4, so I assume it's getting the DD stream.

My unit still displays dialnorm (Offset) 0dB so I'm not seeing any change. Recall that Dolby says that this is supposed to happen although their developer note is clearly wrong about other things so who knows.