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ProLogicII question

instigator

Active Member
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!
 

dante01

Distinguished Member
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.
 
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instigator

Active Member
dante01 said:
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.
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...
 
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instigator

Active Member
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?
 

dante01

Distinguished Member
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?

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?
 

instigator

Active Member
dante01 said:
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?
Thanks dude!
 

dante01

Distinguished Member
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?
There is no such option.

Choose passthrough in relation to the actual audio present ;)




and here is what you did:
 
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dante01

Distinguished Member
er, you mean like this:
image
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.
 

instigator

Active Member
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.
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...
 

dante01

Distinguished Member
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...
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:

 
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dante01

Distinguished Member
UPDATE

From the Handbrake manual:

Another method is to create 5.1 channel AAC audio tracks. For the Track Mix, select "6 channel discrete" from the drop-down menu, and your movie will contain discrete surround sound in the modern AAC format. This takes up less space than AC3: instead of 448kbps, you can do well with 384kbps (64 kbps per channel). Its real benefit is that it doesn't make QuickTime barf. Sadly, it is very difficult to hear all those discrete channels of sound. It cannot be sent over an optical cable to a home theater amp. If you try, whether on a Mac or an AppleTV, you will only hear "downmixed" surround sound, similar to Dolby Pro Logic. To hear the discrete surround sound in all its glory, you will need to attach an analog surround sound device to your Mac. One popular device is the Griffin FireWave. Then, you have to attach a cable to your amp/receiver for each of the six speaker channels. It cannot be done over optical/HDMI.
https://trac.handbrake.fr/wiki/SurroundSoundGuide
 

instigator

Active Member
dante01 said:
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!
 

dante01

Distinguished Member
Now to worry about hd audio... Woo hoo!
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?
 

instigator

Active Member
dante01 said:
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?
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...
 

dante01

Distinguished Member
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dante01

Distinguished Member
Makemkv does handle hd audio now....
okay :)


MakeMKV 1.4.10 Released – HD Audio Support Finally Added

Version 1.4.10 of MakeMKV has just been released. One of the biggest gripes with MakeMKV (and the reason why I stopped using for my Blu Ray collection) is that it did not support HD Audio (TrueHD/DTS-MA), it would only extract the core audio. Well, finally with this release MakeMKV fully supports HD Audio. I had a chance to test out on a few different movies that contained DTS(MA) or TrueHD and in each case MakeMKV created a perfect 1:1 copy of the movie. The only feature missing for me is the ability to create a secondary AC3 track. This can be done with TrueHD since AC3 is the core, but with DTS(MA) MakeMKV will only extract the DTS core. Right now I need a secondary AC3 track because one of the media players in my house does not support HD audio nor will it downmix. Maybe the answer is just to ditch that player already since it seems like all new players will have some sort of support for HD audio and stop worrying about AC3??? The other option would be to use MakeMKV, and then use a program like Popcorn MKV Audio Converter to create the AC3 track. And of course another option would be to use a combination of Clown_BD and MKVMerge (which I do currently). One other important note is that MakeMKV does not require a 3rd party software like AnyDVD. The only question though since MakeMKV only gets updated periodically is how will it handles decryption for newer movies. Choices, choices, choices…

Changelog:
MakeMKV v1.4.10
New functionality: instant video streaming
Added support for all blu-ray HD audio tracks:
Dolby TrueHD
Dolby Digital plus (E-AC3)
DTS-HD
DTS-HD Losless (Master audio)
DTS-HD Low bitrate
Corrected drive access problems on Windows (AHCI)
Corrected “MKV_ASSERT” error on titles with many subtitle tracks
Miscellaneous stability improvements
MakeMKV 1.4.10 Released – HD Audio Support Finally Added : A Digital Home Blog
 
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