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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 bodosom,

    bodosom bodosom Nov 27, 2015 9:32 AM in response to HAL9000.2
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 9:32 AM in response to HAL9000.2

    HAL9000.2 wrote:

    Do you have the means to check the original AC-3 file for metadata like dialnorm?

    No but it's unlikely dialnorm would be zero and certainly not across multiple inputs.  The default is -4dB but it's not fixed and I suppose -4dB could be displayed as 4 since it's always negative.  The simpler explanation is the ATV4g is doing "adjustments" and then setting dialnorm to zero so the downstream device won't undo those adjustments.   I think most people are of the opinion that those adjustments should only be made if compression has been enabled.  Apple is apparently of the opinion that it's "better" to always process even the processing is a no-op with respect to volume.

  • by bodosom,

    bodosom bodosom Nov 27, 2015 9:37 AM in response to bodosom
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 9:37 AM in response to bodosom

    bodosom wrote:

    ...  As you noted dialnorm is in the bitstream and is set by the sound editor (or equivalent) for each movie in the range 1

    I clearly can't type today.

     

    "in the range 1 [to 31]"

     

    However rereading does make me wonder if that range is how it's displayed on the encoder with an implicit negation and if the typical value of -27dBfs is set with 27 (absolute value) or 4 (offset from 31).

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 27, 2015 10:00 AM in response to bodosom
    Level 1 (10 points)
    Nov 27, 2015 10:00 AM in response to bodosom

    Dialnorm is a number between 1 and 31. The values translate to -1dB to -31dB below full scale. -31 = no gain reduction, -1 = 30dB of gain reduction.

  • by Jon Walker,

    Jon Walker Jon Walker Nov 27, 2015 11:21 AM in response to HAL9000.2
    Level 6 (18,620 points)
    Nov 27, 2015 11:21 AM in response to HAL9000.2

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

    Thanks for the link to the referenced article. It basically confirms what I had originally thought. Am, however, still wondering if the display value is based solely on the AC3 encode, the AVR calibration, or a net result of the two in combination. (Just curious as to whether you happen to know for sure.)

    SJAUG.png

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 27, 2015 11:35 AM in response to Jon Walker
    Level 1 (10 points)
    Nov 27, 2015 11:35 AM in response to Jon Walker

    The dialnorm number is part of the AC-3 stream metadata. It is set when the bitstream is encoded. Basically it signals the average dialog level in the program. For example, if the average level is -27dBFS then dialnorm has to be set to 27. The AVR then reduces program level by 4dB (31-27=4) during playback.

  • by bodosom,

    bodosom bodosom Nov 27, 2015 11:36 AM in response to HAL9000.2
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 11:36 AM in response to HAL9000.2

    HAL9000.2 wrote:

     

    Dialnorm is a number between 1 and 31. The values translate to -1dB to -31dB below full scale. -31 = no gain reduction, -1 = 30dB of gain reduction.

    I've read the Wikipedia article too.  That doesn't explain the "notation" used by the pictured Pioneer which shows DIAL NORM +4.  Obviously +4 doesn't mean 27dB of gain reduction (4 on a scale of 1 to 31) it means add 4 to -31dB to get the default -27dB which you would say is a dialnorm of 27.


    In any case the ATV4g is (currently) modifying the bitstream in Dolby mode presumably to support volume management and presumably by doing a decode/encode. Another example would be a particular Netflix Orginals episode at -5dB or a movie at -4dB.  Both show 0 (or missing) on the ATV4gen.

  • by HAL9000.2,

    HAL9000.2 HAL9000.2 Nov 27, 2015 11:56 AM in response to bodosom
    Level 1 (10 points)
    Nov 27, 2015 11:56 AM in response to bodosom

    I agree this behavior suggests that Apple TV 4 is doing a live and probably lossy AC-3 re-encode. Bitstream pass-through should be default behavior instead or at least an optional settings for people that don't want the device to tamper with audio quality.

  • by bodosom,

    bodosom bodosom Nov 27, 2015 12:34 PM in response to HAL9000.2
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 12:34 PM in response to HAL9000.2

    HAL9000.2 wrote:

     

    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?

    My earlier answer of no was based non-local sources.  That's unduly limiting.  As far as I know you can't determine much about FairPlay audio streams and of course streamed data is, well, streamed.  However mediainfo (at least under Linux) will display dialnorm if it's not under DRM. I checked an on-disk unencrypted movie that reported zero on the ATV4gen and -4dB on the ATV3gen and the dialnorm is reported as -27dB.

     

    So yes for on-disk unencrypted AC-3 and no for anything else.  As far as I know.

  • by Jon Walker,

    Jon Walker Jon Walker Nov 27, 2015 5:49 PM in response to HAL9000.2
    Level 6 (18,620 points)
    Nov 27, 2015 5:49 PM in response to HAL9000.2

    I agree this behavior suggests that Apple TV 4 is doing a live and probably lossy AC-3 re-encode. Bitstream pass-through should be default behavior instead or at least an optional settings for people that don't want the device to tamper with audio quality.

    I tend to disagree. The current evidence only suggests that the metadata is being manipulated. Until such time as the output is compared with and without TV4 processing between the source and AVR, it seems more likely that the encoded "audio" data itself is being passed to the receiver unchanged—e.g., like copying data from an M4V file container to an MOV file container without actually transcoding any of the stored data. Apparently my definition of "pass through" strategy is more liberal than that of others. If I encode an AC3 track as 1.0 mono and the AVR receives an AC3 bitstream with 1.0 audio data untranscoded, to my mind the data was "passed through" by the bitstream whether or not any metadata was changed or lost. The same holds true for 2.0, 2.1, ..., 5.1 encoded audio. This is exactly what appears to be happening to my files in the "Dolby Surround" mode when sourcing the AC3 encoded audio rack.

    SJAUG.png

  • by Jon Walker,

    Jon Walker Jon Walker Nov 27, 2015 5:51 PM in response to bodosom
    Level 6 (18,620 points)
    Nov 27, 2015 5:51 PM in response to bodosom

    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.

    While the "+4" may be a constant, it may not actually be a dialnorm value. Could it actually be the "stored adjustment" the receiver is supposed to apply to any recognized AC3 bitstream based on the calibration performed during initial setup of the receiver and speakers?

     

    As to playing the "same" AC3 source, I currently get the +4 value streaming "the same" M4V library files encoded by me from the iTunes server, Air Video server (via indirect Air Play only), Air Video HD server, Plex Server, or Air Play (as compatible) directly to an TV2, TV3, TV4, LG BD Player, Oppo BD Player or LG HDTV (audio redirected back to the AVR), as well as, indirect Air Play playback from both iPad and iPhone mobile devices. DVD and BD optical discs also have the same "+4" display value (when applicable) and I most recently noted "on the fly" DTS 5.1 to AC3 transcode streams from the Plex Server for RAID stored backups of DVD/BD content also have this display value. All of which brings me back to the question of whether or not the "+4" display might merely refer to a programmed adjustment. (I.e.,, I even see this for 1.0/2.0 AAC audio tracks which the TV4 outputs via an AC3 5.1 bitstream connection in the TV4 "Dolby Surround" mode which are definitely the product of TV4 non-pass through "machinations" as programmed by Apple.)

    SJAUG.png

  • by bodosom,

    bodosom bodosom Nov 27, 2015 7:19 PM in response to Jon Walker
    Level 1 (28 points)
    iPhone
    Nov 27, 2015 7:19 PM in response to Jon Walker

    Jon Walker wrote:

     

    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.

    While the "+4" may be a constant, it may not actually be a dialnorm value. Could it actually be the "stored adjustment" the receiver is supposed to apply to any recognized AC3 bitstream based on the calibration performed during initial setup of the receiver and speakers?

    As I said, what seems a long time ago, only if your AVR is misleading you since it says DIAL NORM.  Dialog Normalization isn't constant and it's independent of AVR settings unless your decoder is broken and presumably fails to meet Dolby certification.  As previously noted mediainfo (available on most common platforms) will display dialnorm in an unencrypted disk file.  I have values from -27dB to -31dB.  By the way my AVR displays dialnorm -31dB differently from no dialnorm.

     

    If you have Netflix check Jessica Jones episodes 1 and 2.  Episode one has dialnorm -5dB and episode two has dialnorm -4dB on both my ATV3 and my TiVo.  Both are reported as 0/missing via the ATV4gen (with Surround Dolby).

  • by Jon Walker,

    Jon Walker Jon Walker Nov 27, 2015 8:47 PM in response to bodosom
    Level 6 (18,620 points)
    Nov 27, 2015 8:47 PM in response to bodosom

    As I said, what seems a long time ago, only if your AVR is misleading you since it says DIAL NORM.  Dialog Normalization isn't constant and it's independent of AVR settings unless your decoder is broken and presumably fails to meet Dolby certification.  As previously noted mediainfo (available on most common platforms) will display dialnorm in an unencrypted disk file.  I have values from -27dB to -31dB.  By the way my AVR displays dialnorm -31dB differently from no dialnorm.

    MediaInfo for audio tracks in a typical M4V iTunes managed library file:

    Screen Shot 2015-11-27 at 10.47.39 PM.png

    Where am I supposed to find the Dialnorm info?

     

    If you have Netflix check Jessica Jones episodes 1 and 2.  Episode one has dialnorm -5dB and episode two has dialnorm -4dB on both my ATV3 and my TiVo.  Both are reported as 0/missing via the ATV4gen (with Surround Dolby).

    TV4 Netflix app:

    Episode 1: plays as DD5.1 w/Dialnorm +4

    Episode 2: plays as DD5.1 w/Dialnorm +4

     

    TV3 Netflix app:

    Episode 1: plays as DD5.1 w/Dialnorm -1

    Episode 2: plays as DD5.1 does not cycle through Dialnorm display

     

    Oppo Netflix app:

    Episode 1: plays as user selectable Stereo PCM or DD+5.1 w/Dialnorm -1

    Episode 2: plays as user selectable Stereo PCM or DD+5.1 but does not cycle through Dianlnorm display

     

    Handbrake encoded files display "Dialnorm +4" on both TV3 and TV4 when playing the AC3 track in respective "Computers" apps using "Auto" mode for TV3 and "Dolby Surround" for TV4.

    SJAUG.png

  • by bodosom,

    bodosom bodosom Nov 28, 2015 6:53 AM in response to Jon Walker
    Level 1 (28 points)
    iPhone
    Nov 28, 2015 6:53 AM in response to Jon Walker

    The GUI version of mediainfo only shows basic data.  I normally use Linux for things like this but mediainfo is available via Homebrew.  Given only the dialnorm display results you've shown it would appear that your AVR is not actually displaying dialnorm or it's faulty.  Dialog normalization happens in the (E-)AC-3 decoder and a display of that value should just reflect the input parameter.  By the way, dialnorm is not meta-data -- it changes the output.

     

    $ for i in Dolby*;do echo $i;mediainfo -f $i|grep dialnorm;done
    Dolby-City.m4v
    dialnorm                                 : -27
    dialnorm/String                          : -27 dB
    dialnorm_Average                         : -27
    dialnorm_Average/String                  : -27 dB
    dialnorm_Minimum                         : -27
    dialnorm_Minimum/String                  : -27 dB
    dialnorm_Maximum                         : -27
    dialnorm_Maximum/String                  : -27 dB
    dialnorm_Count                           : 32
    Dolby-Egypt.m4v
    dialnorm                                 : -31
    dialnorm/String                          : -31 dB
    dialnorm_Average                         : -31
    dialnorm_Average/String                  : -31 dB
    dialnorm_Minimum                         : -31
    dialnorm_Minimum/String                  : -31 dB
    dialnorm_Maximum                         : -31
    dialnorm_Maximum/String                  : -31 dB
    dialnorm_Count                           : 32

  • by Jon Walker,

    Jon Walker Jon Walker Nov 28, 2015 11:33 AM in response to bodosom
    Level 6 (18,620 points)
    Nov 28, 2015 11:33 AM in response to bodosom

    By the way, dialnorm is not meta-data -- it changes the output.

    Sorry! As explained in another discussion in which you participated, this is not my area of expertise. I merely used the term in reference to the phrase "meta data parameter" as per HAL9000's linked article. I tend to think of it as a "playback" or "rendering" instruction embedding in the source file—much like "current" playback dimensions or targeted aspect ratio settings which are independent of the compressed data actually stored in a file.

     

    The GUI version of mediainfo only shows basic data.  I normally use Linux for things like this but mediainfo is available via Homebrew.

    Well, that explains that. Unfortunately, I currently don't have the time required to learn how to use/communicate with this version of the app at such a low level. While I might look into this further next year when/if I have the time, I rarely pay much attention to Dialnorm displays and am more concerned with proper channelization than comparative level standards that I probably can't accurately hear/differentiate aurally in any case at my age.


    Given only the dialnorm display results you've shown it would appear that your AVR is not actually displaying dialnorm or it's faulty.  Dialog normalization happens in the (E-)AC-3 decoder and a display of that value should just reflect the input parameter.

    I'm leaning more towards what I consider a more simple explanation that both explains and correlates the differences we are seeing. I notice you say that a display of the dialog normalization value "should" just reflect the input parameter. What if we posit that my receiver displays the net adjusted input parameter plus my receiver's calibrated adjustment for speaker location/orientation and follow that logic:

     

    1. As previously stated, my receiver was calibrated (for a somewhat strangely "landscape" shaped "Home Theater" viewing area having a wider than normal Left/Right speaker separation and a narrower than normal Front/Rear speaker separation). As a result, it appears to have a "+ 4" dialog normalization adjustment programmed into the system.
    2. As previously indicated, all (but one) of my iTunes managed video library files were encoded by me with a zero gain level target. However, since I have no way to examine these files other than your suggested workflow (which I am reluctant to try without a lot more information), I can't even determine if my files contain a valid dialog normalization setting—let alone a valid 0 db equivalent (which is, at best, only an assumption at this point). In either case, let's see what happens if we continue under the assumption that the dialog normalization is either 0 db or missing...
    3. In the case of my TV2 and TV3 test, my encoded files display an adjusted value of "0" plus my "+4" adjustment or a net "+4" adjusted value which I do see and have previously reported.
    4. In the case of your Jessica Jones episode 1 file, you see a dialog normalization value of "-5 db" while I see "-1" which is the net adjusted value for a "-5db" input value plus my receiver's "+4" adjustment when both of use a TV3 device for playback.
    5. In the case of your Jessica Jones episode 2 file play through TV3 devices, you see a dialog normalization value of "-4 db" while I get no dialog normalization display for the adjusted "-4 db" plus my "+4" receiver adjustment which provides a "0" net adjusted value which you (and others) have indicated can produce inconsistent value displays by various receiver brands and models.
    6. On the other hand, both Jessica Jones episodes on the TV4 produce "0/missing" readings on your system but return a "0/mising" plus my "+4" adjustment or "+4" net adjusted display on my system.
    7. Your TiVO and my Oppo Netflix app alternatives both produce the same consistency in results as paragraph 3 and 4 above.

     

    In any case, applying Occam's Razor, this hypothesis seems to currently be the simplest, and thus, preferred explanation until something better comes along. Was however, wondering if you could/would download and examine a couple of test files already posted to determine if they contain valid or 0/missing dialog normalization values:

    http://downloads.walker4.me/Temporary_files/Test-1.m4v

    http://downloads.walker4.me/Temporary_files/Test-2.m4v

    http://downloads.walker4.me/Temporary_files/Test-3.m4v

    SJAUG.png

  • by bodosom,

    bodosom bodosom Nov 28, 2015 1:53 PM in response to Jon Walker
    Level 1 (28 points)
    iPhone
    Nov 28, 2015 1:53 PM in response to Jon Walker

    Your test files all have a dialnorm of -31dB.  If your AVR does display something other than dialog normalization despite the label then I hope it has an option that you activated that enables that "feature".

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