ProLogicII question

Discussion in 'AV Receivers & Amplifiers' started by instigator, Jan 3, 2012.

  1. instigator

    instigator
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    I was experimenting with 2 codecs for 6 channel audio passthrough on my apple tv 2

    AAC at 768kbps 6channel passthrough vs ac3 6 channel passthrough at 600 something or other Kbps

    The handbrake default appletv 2 setting is track 1 AAC PLII at 160 which I bump up to 320 (the max allowed) and track 2 ac3 passthrough 6 channel at 612 or something Kbps....

    I understand that AAC is a newer codec and on paper is higher quality but isn't as widely playable as ac3 hence handbrake using ac3...

    My Denon 1610 automatically plays the 2nd track, the 5.1 track...

    I ripped a couple chapters of Captain America using both codecs....

    The AAC one sounded a bit brighter and like it had more transparent airy quality which then made the ac3 track sound dull....

    My question is that my Denon displayed the PLII light... Is it still playing 6 discreet channels or down mixing to two channels and processing it as PLII two channels? Or is it just displaying that light for some reason and it's playing 6 discreet channels?

    I think a blind test would be more interesting but I'm intrigued by the results so far... I can't wait to try HD audio!
     
  2. dante01

    dante01
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    AAC can only have 2 discrete channels of audio and you matrixed any additional channels into those two when you encoded it. AC3 is Dolby Digital and it can hold 8 discrete channels without need to matrix. PLII isn't a format, it is a means of either creating faux multichannel surround or extracting matrixed channels from discrete channels. Pro LOgic is regarded as being inferior when compared to discrete surround formats. You matrixed the extra channels into the AAC when you selected PLII as the audio mixdown.

    Also note that rencoding 160kb/s as 320kb/s doesn't improve quality, it just wastes the memory required to store the resulting file.

    If you want the best quality audio from rips then use passthrough and do not re encode the audio at all.
     
    Last edited: Jan 3, 2012
  3. instigator

    instigator
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    Thanks for your reply...

    Are you saying on disc the audio is at 160kbps? I understand that if that is the audio quality on disc, increasing the bitrate just takes more space and doesn't increase quality... But my understanding is that handbrake default settings are geared towards saving space so all the settings can be bumped up...

    But I do see your point... If ac3 is using compression does it equate to something like 128kbps per each of the 6 channels to make the 600 or so Kbps in total, or am I misinterpreting this number? If each track is at something like 128 of the the 6 channel ac3 then why downmix it to 2 channel 320? I'm guessing that if we are summing together this 600 some odd Kbps of stuff that when it's output to 2 channel doing it at 320kbps will sound better? But I understand how this could be overly optimistic and flawed thinking....

    I also, it appears that other people on the interweb are referring to 6 channel AAC codec.... That's why I'm asking you guys... Is it real or just a mislabeled setting in handbrake or bug or something?

    By the way, the source is hd audio... But still trying to figure out how exactly handbrake is dealing with it... It appears it now can handle it...
     
    Last edited: Jan 3, 2012
  4. instigator

    instigator
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    On the Denon display I get this:

    Ac3 6 channel passthrough Denon shows: Dig, Dolby Digital

    AAC 6 channel passthrough Denon shows: PCM, Dig, Dolby logo and PLII

    But I just check audio input signal going through a few menus on the Denon... And bingo, for AAC version it's showing signal is PCM, 48khz, format 2/0/0

    The ac3 version is showing Dolby Digital, 48khz, format 3/2/.1

    So handbrake is being silly for showing an AAC 6 channel passthrough option?
     
  5. dante01

    dante01
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    No, I'm just pointing out that increasing the bit rate doesn't necessarily improve the quality of the audio. AAC is a lossy encoding process and you will lose detail regardless of the bit rate you use. The original rate of the native AC3 audio will of far exceeded that which you used when you re encoded it as AAC. AC3's bitrate is not a cumulative sum (per channel), but is the bitrate used when it was encoded. Channels are not encoded individuallyat different rates.

    The only reason for re encoding is to save space, but you lose data each and every time you do this. It is far better to passthrough audio and save it along with the video data. This way you get exactly what was on the disc to begin with. AC3 audio such as Dolby Digital on DVD titles doen't occupy that much space anyway so there's no real benefit to rencoding it at a lower bitrate or using lossy compression to save storage space.

    THere is a discrete HE-AAC format that is used for TV broadcasts, but it requires a specific codec and not many devices employ it. Even Freeview boxes transcode AAC-HE audio to AC3 in order to maintain compatability. I think AAC-HE has the capability to hold 98 discrete audio channels?
     
  6. instigator

    instigator
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    Thanks dude!
     
  7. dante01

    dante01
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    There is no such option.

    Choose passthrough in relation to the actual audio present ;)

    [​IMG]


    and here is what you did:
    [​IMG]
     
    Last edited: Jan 3, 2012
  8. instigator

    instigator
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    er, you mean like this:
    [​IMG]
     
  9. dante01

    dante01
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    Yes, but in that instance the native audio is DTS-HD and not AC3. Use the MKV container option and then choose passthru on both the codec and mixdown audio dropdowns. DTS-HD Master Audio is a lossless codec and not to be confused with lossy DTS or AC3.
     
  10. instigator

    instigator
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    i understand what you are saying... however doesn't it seem strange that handbrake is showing AAC 6 channel option when it doesn't exist?

    I did find HE-AAC which i am ripping a couple chapters of right now to see if it plays on my Denon and if it shows up as 6 channel audio...
     
  11. dante01

    dante01
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    But the option is in the mixdown dropdown. I do agree that they could of phrased it better, but mixdown sort of tells you what that option does ;)

    I'm not even sure DTS-HD can be transcoded or rencoded? It uses the core DTS audio and not the full blown HD audio.

    The important option is the 'codec". This determines whether the audio is passed through or which codec to use to rencode the audio.

    You can select the 6 channel discrete mixdown option with any of the other codecs and it isn't anything particularly to do with AAC:

    [​IMG]
     
    Last edited: Jan 3, 2012
  12. dante01

    dante01
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    UPDATE

    From the Handbrake manual:

    https://trac.handbrake.fr/wiki/SurroundSoundGuide
     
  13. instigator

    instigator
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    Thanks... This sounds familiar to what I have read... But was told that hdmi would carry the AAC 6 channel audio... Looks like they were wrong...

    FYI the test rip of he-AAC 6 channel still showed up as 2 channel audio on the Denon via hdmi from appletv 2...

    I do have an old Denon 3802 with analogue inputs but I think I'll just skip this AAC vs ac3 thing for now....

    Now to worry about hd audio... Woo hoo!
     
  14. dante01

    dante01
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    I think you are limited to the higher rate SD core audio when dealing with the HD codecs? You can make iso images of your BD titles and have the full blown HD audio, but I don't think it possible to passthrough the HD audio formats for use with other video containers?
     
  15. instigator

    instigator
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    Right... What I'm hoping is That I can rip once and then when appletv 3 comes out or I switch to different streaming box etc that the hd audio will stream then... I just don't want to be ripping my collection twice in a year from now.... Heh heh...
     
  16. dante01

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    Last edited: Jan 3, 2012
  17. instigator

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  18. dante01

    dante01
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    okay :)


    MakeMKV 1.4.10 Released – HD Audio Support Finally Added : A Digital Home Blog
     
    Last edited: Jan 3, 2012

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