Dolby Pro Logic test audio

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zigzag
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Joined: Sat Mar 31, 2007 9:40 pm

Dolby Pro Logic test audio

Post by zigzag »

Does anyone know of a downloadable audio file that I can use to test with my Pro Logic II receiver to which my Apple TV is connected? I'd like to hear for myself that all 5 channels are receiving independent signals.

Thanks.
deckeda
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Post by deckeda »

A proper test likely isn't an audio file, but rather a video file with a surround-sound audio track as part of it.

The difference is the file container, and how it gets encoded (which is why we're all here, right) and further how AppleTV treats what its fed.

So just find a relevant chapter on a DVD you're familiar with and encode it.
realityking
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Post by realityking »

From my understanding there is nothing AppleTV does with an PLII Track but outputting it, everything else is done by the receiver.
nightstrm
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Post by nightstrm »

Right, to AppleTV (and any other device for that matter) it is just another stereo audio track.
maurj
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Post by maurj »

Hi ZigZag,

To test the whole process - from HandBrake ripping to playback - use the test disk image I created whilst coding the DPLII support. It's available here:

http://www.maurj.com/5_1_DOLBY.htm

Right-click on 5_1_DOLBY.iso.zip to download it, then unzip it and rip 5.1 AC3 audio with HandBrake. This DVD image has a test track which speaks the channel name in that channel only.

- maurj.
zigzag
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Joined: Sat Mar 31, 2007 9:40 pm

Post by zigzag »

Thanks very much, maurj. I will give it a try tonight when I get home. I've already ripped the "globe THX" from the start of "Revenge of the Sith" as DPLII and it sure seems to do the job.
zigzag
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Joined: Sat Mar 31, 2007 9:40 pm

Post by zigzag »

Maurj,

I noticed the image on the file indicates all 6 speakers should sound. I thought DPLII was only 5 channel?

Thanks
bladerunner
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Post by bladerunner »

Thanks maurj - that is exactly what I was looking for so I could test my home theater system with AppleTV.
rhester
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Post by rhester »

zigzag: It's maurj's test DVD I sent you the link to my test rip of via PM a few days back when you asked. =)

DPL II is 5.0 without LFE or 5.1 with - I encoded with LFE for the purpose of that exercise. If you consider LFE a 'channel', then DPL II is most definitely capable of six.

Basically, DPL II is referred to as 5-channel because a) Dolby advises against use of LFE unless required and b) 6-channel generally refers to center left and center right, where DPL II only supports center (main).

Rodney
maurj
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Post by maurj »

...and Handbrake's current DPLII implementation is 5.0, not 5.1. My test DVD image has an LFE channel - but you should expect it to be dropped when ripping the test DVD with HandBrake using DPLII.
zigzag
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Joined: Sat Mar 31, 2007 9:40 pm

Post by zigzag »

Rodney - sorry I missed your PM. I've changed my profile to give me the pop-up. Thanks for that info.

I think I understand the 5.0 vs 5.1 in DPLII - thanks for the clarification to both of you. Whether it's 5.0 or 5.1, I'm a very happy clam. The development team has done a fabulous job on Handbrake and my Apple TV is a much better system now that I can encode in DPLII. It's just a pain to have to go back and reconvert all my DVDs. I think I'll train my 6 year old to do it for me and pay her something like $0.50 per disk. Would that violate child labor laws? :D
lemon
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Joined: Tue Apr 24, 2007 2:27 am

Post by lemon »

maurj wrote:...and Handbrake's current DPLII implementation is 5.0, not 5.1. My test DVD image has an LFE channel - but you should expect it to be dropped when ripping the test DVD with HandBrake using DPLII.
Hi Maurj, are there any plans to implement LFE in HandBrake's DPLII encoding? Or are there constraints preventing it?

Thanks!

-lemon
d70mac
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Post by d70mac »

These are pages from the Dolby web site that might help everyone with definitions:

http://www.dolby.com/professional/pro_a ... round.html

http://www.dolby.com/professional/pro_a ... taltv.html

If you process a Dolby Digital (AC3) movie using the "Dolby Pro Logic II" setting it will create 2 channels -- left and right that can be transformed into a left, center, right, left surround and right surround. You can confirm that it creates only two channels by opening a Handbrake-processed Dolby Digital 5.1 movie in Quicktime and then examining the soundtrack audio settings.

Conversely, processing using the "6-channel discreet" will create 6 separate channels in Quicktime. But since they are encoded AAC streams that are not supported by any receiver or video controller I know of and the AppleTV only has left and right analog outputs I can't see of a way to play discreet Dolby Digital 5.1 using an AppleTV.

It might be possible with DTS but that's because it was designed to be carried discreet over 2 channels.

On my home theater system Dolby Prologic II is markedly inferior to Dolby Digital AC3 (aka Dolby Digital 5.1) and the home theater is the target location for the AppleTV.

This isn't something that Handbrake developers could fix. Besides, they already do enough!
mallbritton

Re: Dolby Pro Logic test audio

Post by mallbritton »

zigzag wrote:Does anyone know of a downloadable audio file that I can use to test with my Pro Logic II receiver to which my Apple TV is connected? I'd like to hear for myself that all 5 channels are receiving independent signals.

Thanks.
If you want to hear AppleTV output Dolby Digital or DTS 5.1 audio you can download the sample files from this site: http://www.diatonis.com/downloads_dts_ac3.html

If your A/V receiver is capable of playing DD and/or DTS 5.1 audio you will hear the files correctly. Otherwise you will hear only static. You must have the AppleTV connected to your receiver via an optical audio cable, also known as TOSlink.
maurj
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Post by maurj »

Hi lemon,

It should be possible to implement DPLII with LFE, to give a 5.1 mix. I did give this a try for HandBrake 0.8.5b1, but it wasn't as easy as I'd expected, due to the way liba52 works (it doesn't expect to extract the separate LFE track when creating output with non-discrete channels). It's certainly doable with a further patching of liba52. Not sure I'll get the time to do it soon, so if anyone else wants to give it a try, they'd be welcome!

- maurj.
d70mac
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Post by d70mac »

Here's what Dolby Labs has to say about mixing down a discreet 5.1 mix to Pro Logic II and adding an LFE channel...
Dealing with LFE Signals
In a typical 5.1 downmix the LFE signal is not used. This is true for every Dolby Digital decoder ever built into a consumer product. When the DP563 was designed, the option of including some of the LFE signal was included. However, it needs to be restated that there is no LFE channel provision in the Dolby Pro Logic II matrix. Once the information from the LFE channel is added in, the decoder processes it as Center channel information, or information common to Left and Right channels. In order for the LFE information to get to a subwoofer on playback, the consumer decoder needs to be using bass management and redirecting bass information to a subwoofer. There are other concerns when adding an LFE signal to the mix. If the LFE is simply redistributed within the other channels of the mix, they will usually be subject to some low-frequency bandpass filtering. This filtering causes phase shifts of the LFE signal. When they are acoustically added within a room, these phase shifts are fairly subtle and often go unnoticed. However, when they are electronically added together with the five main channels in the encoder, they may produce less than desirable results at certain frequencies. For this reason, it is recommended that the LFE signal not be used in a Dolby Pro Logic II downmix unless it contains unique information that is not repeated in any of the five main channels.
The full document can be found here...

http://www.dolby.com/assets/pdf/tech_li ... nology.pdf
maurj
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Post by maurj »

d70mac,

Absolutely spot on (we debated this at length when deciding if we should include DPLII+LFE at all, were it to be possible with the libraries we use). For some DVDs it'll work great - for others, which have some of the LFE signal in the other 5 channels, there'll be this phase shift. If we do implement DPLII+LFE, it'll certainly be optional, and won't be the default (that would probably remain just DPLII).

- maurj.
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