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Q: AppleTV 4 surround sound issue

i just acquired an AppleTV 4 to replace my AppleTV 3. Since I used to connect the optical audio out to my Yamaha surround sound receiver, I am forced to use only hdmi. That would not be a problem for two reasons:

 

1. All AppleTV content plays with the receiver showing PCM and not DTS or some other form of surround sound.

2. All my movies i encoded are strictly playing in stereo only. The DTS stream is seemingly not being passed through hdmi.

 

Routing hdmi to tv then optical from tv to receiver does not change anything.

 

How can I fix this?  Surely I should be getting DTS with a Yamaha rx- v1900 receiver?

Posted on Nov 1, 2015 1:32 AM

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Q: AppleTV 4 surround sound issue

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  • by jvulto,

    jvulto jvulto Nov 25, 2015 4:08 AM in response to W.R.R. Farid
    Level 1 (4 points)
    Nov 25, 2015 4:08 AM in response to W.R.R. Farid

    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?

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 25, 2015 4:21 AM in response to jvulto
    Level 1 (10 points)
    Nov 25, 2015 4:21 AM in response to jvulto

    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.

  • by W.R.R. Farid,

    W.R.R. Farid W.R.R. Farid Nov 25, 2015 4:45 AM in response to jvulto
    Level 1 (0 points)
    Nov 25, 2015 4:45 AM in response to jvulto

    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.

  • by bodosom,

    bodosom bodosom Nov 25, 2015 6:26 AM in response to W.R.R. Farid
    Level 1 (28 points)
    iPhone
    Nov 25, 2015 6:26 AM in response to W.R.R. Farid

    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.

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 25, 2015 6:41 AM in response to bodosom
    Level 1 (10 points)
    Nov 25, 2015 6:41 AM in response to bodosom

    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.

  • by bodosom,

    bodosom bodosom Nov 25, 2015 7:12 AM in response to HAL9000.2
    Level 1 (28 points)
    iPhone
    Nov 25, 2015 7:12 AM in response to HAL9000.2

    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.

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 25, 2015 7:42 AM in response to bodosom
    Level 1 (10 points)
    Nov 25, 2015 7:42 AM in response to bodosom

    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.

  • by bodosom,

    bodosom bodosom Nov 25, 2015 11:13 AM in response to HAL9000.2
    Level 1 (28 points)
    iPhone
    Nov 25, 2015 11:13 AM in response to HAL9000.2

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

  • by W.R.R. Farid,

    W.R.R. Farid W.R.R. Farid Nov 26, 2015 4:27 AM in response to pwnell
    Level 1 (0 points)
    Nov 26, 2015 4:27 AM in response to pwnell

    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

  • by Jon Walker,

    Jon Walker Jon Walker Nov 27, 2015 7:57 AM in response to bodosom
    Level 6 (18,620 points)
    Nov 27, 2015 7:57 AM in response to bodosom

    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:

    IMG_0014.JPG

    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.)

    SJAUG.png

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 27, 2015 8:06 AM in response to Jon Walker
    Level 1 (10 points)
    Nov 27, 2015 8:06 AM in response to Jon Walker

    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

  • by bodosom,

    bodosom bodosom Nov 27, 2015 8:35 AM in response to Jon Walker
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 8:35 AM in response to Jon Walker

    Jon Walker wrote:

     

    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: (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.)

     

    I'm not what this means because dialog normalization isn't a constant however my point was if you compare the the dialnorm display for the "same" AC-3 source (e.g. play the same movie from your iTunes server) you'll see one value on the ATV3gen and another value (or in my case no value) on the ATV4gen.

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 27, 2015 8:42 AM in response to bodosom
    Level 1 (10 points)
    Nov 27, 2015 8:42 AM in response to bodosom

    In that case the ATV 3 could have tampered with dialnorm and the ATV 4 is pass-through. Do you have the means to check the original AC-3 file for metadata like dialnorm?

  • by bodosom,

    bodosom bodosom Nov 27, 2015 8:59 AM in response to HAL9000.2
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 8:59 AM in response to HAL9000.2

    HAL9000.2 wrote:

     

    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.

    I was unclear.  You have to compare the same AC-3 stream out the ATV4g and something else.  In my case I compare and ATV3,1(8.3) to an ATV5,3(9.0.1). The data below is from the web interface in my AVR.

    MI:Rogue Nation on ATV3,1(Dolby,Auto):

    Surround ModeDOLBY DIGITAL
      Input SignalDolby Digital
      Fs48kHz
      Format3/2/.1
      OffSet-4dB

     

    MI:Rogue Nation on ATV5,3 (Surround,Dolby):

    Surround ModeDOLBY DIGITAL
      Input SignalAnalog
      Fs48kHz
      Format3/2/.1
      OffSet0dB

     

    Note that the latter calls the Input Signal analog (thats the hint I mentioned) the OSD for the same info calls both input signals DD.  As you noted dialnorm is in the bitstream and is set by the sound editor (or equivalent) for each movie in the range 1

  • by bodosom,

    bodosom bodosom Nov 27, 2015 9:00 AM in response to bodosom
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 9:00 AM in response to bodosom

    bodosom wrote:

     

    Jon Walker wrote:

     

    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: (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.)

     

    I'm not what this means because dialog normalization isn't a constant however my point was if you compare the the dialnorm display for the "same" AC-3 source (e.g. play the same movie from your iTunes server) you'll see one value on the ATV3gen and another value (or in my case no value) on the ATV4gen.

    Feh, I meant to say "I'm not sure what this means .... (and mine is -4dB)".

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