How to output Dolby Pro Logic from Windows XP? - AVS Forum
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post #1 of 12 Old 07-03-2013, 07:04 AM - Thread Starter
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I am running XBMC 11 on a Windows XP machine trough a projector into a Dobly Pro Logic 5.1 amplifier.

here's the setup
HTPC -> Projector (stereo jack) -> Amp (2x RCA connector) -> 5.1 speakers

problem is: only 2 speakers are used when I play ... anything ... on the HTPC

If I use similar setup with the Xbox360 as a DVD player then the sound is appropriately separated - central voice, front&read
XBOX -> Projector(HDMI) -> Amp (2xRCA) -> 5.1 speakers

but if I take the same DVD and play it on the HTPC I loose surround completely

Is there a way to encode Dolby Pro Logic (that my amp understands) into the stereo channels of the computer? Maybe with FFDShow or something?

This technology (Dobly pro logic) is rather old, I was assuming it was "easy" to construct the sound matrix for it and configuration would be painless, but I can't seem to find a way to achieve it. eek.gif

Any pointers welcomed.

-Mars
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post #2 of 12 Old 07-03-2013, 12:43 PM
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What amp and speakers do you have? If the amp is a receiver then its a setting in the receiver, they will have surround modes you can choose from to upconvert stereo to surround.

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post #3 of 12 Old 07-03-2013, 01:08 PM
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there is dolby prologic matrix encoding available in lav audio and ffdshow.
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post #4 of 12 Old 07-03-2013, 01:25 PM - Thread Starter
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Thanks Mindbomb. I never heard of lav audio, but it is my understanding that ffdshow is workable with xbmc. Is there a quick way to test them being functionnal? they need specific players and files or anything will do?

-Mars
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post #5 of 12 Old 07-03-2013, 01:44 PM
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You really should consider going from HTPC straight to reciever. Why bother with Dobly pro logic.

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post #6 of 12 Old 07-03-2013, 02:33 PM - Thread Starter
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the receiver doesn't accept anything else... I really should consider updating. Moreover, the HTPC can output directly in SPDIF.

But in the meanwhile, I would really like to use every speakers, as opposed to only the front ones... frown.gif

-Mars
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post #7 of 12 Old 07-03-2013, 05:53 PM
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Give us the model numbers on the projector and receiver as well as your computer or motherboard.

Quote:
here's the setup
HTPC -> Projector (stereo jack) -> Amp (2x RCA connector) -> 5.1 speakers
How is the sound getting to the projector. Also make sure you have a stereo splitter on the RCAs not a Mono cord

problem is: only 2 speakers are used when I play ... anything ... on the HTPC

If I use similar setup with the Xbox360 as a DVD player then the sound is appropriately separated - central voice, front&read
XBOX -> Projector(HDMI) -> Amp (2xRCA) -> 5.1 speakers

but if I take the same DVD and play it on the HTPC I loose surround completely
Set up your player to output 2.0 stereo NOT bitstream or 5.1, same thing for Windows

Is there a way to encode Dolby Pro Logic (that my amp understands) into the stereo channels of the computer? Maybe with FFDShow or something?
Software encoders aren't going to help you much unless you're using 5.1 analog outputs on the computer.

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post #8 of 12 Old 07-03-2013, 06:12 PM - Thread Starter
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The current computer setup is: Asus P5P800 w/ onboard soundmax. Oddly ennough it is 5.1 compatible and have the possibility to output SPDIF.
The audio out goes to the projector (with the VGA connector) and uses an male-male 3.5mm audio jack cable
The projector is an BenQ MX516
From the MX516 to the amplifier there is an 3.5mm audio jack to stereo RCA connectors
The amplifier isn't per say an audio receiver, it is an very old Curtis DVD/Home Theater (lol) device that does a good job with DVD 5.1 from the xbox's HDMI via the projector. It is a DVD5038 with its DVD bay shut and better speakers.

From the projector to the speakers (wires, amp w/ dolby, speakers) remains the same weither I use the Xbox's HDMI DVD playback or the HTPC, so the problem must reside prior to that. Perhaps the projector will only pass dolby to its output when it comes from HDMI?

On the HTPC side, I've tried all condigurations I could think of. I've read many places we need to set it to stereo and enable virtual surround or such, but even in that configuration, with both LAV audio and FFDShow configured as dolby (or at least I think so) I can't get anything from the surrounds.
I have installed a trial of winDVD - in it we can enable (force) dolby - no change.

My understanding of Dolby Pro Logic is that the 5.1 info is encoded as non-audible audio in a matrix on the left/right channels. I assume that's what we get from the projector when using the HDMI, but somehow it seems we don't have that at all when we use the computer as audio input.

-Mars
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post #9 of 12 Old 07-03-2013, 08:37 PM
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Is the audio cable attached to your VGA cable Stereo or Mono?

Try connecting HTPC directly to receiver, leave the projector out.
Again, on the HTPC turn off anything that says dolby. You want PCM 2.0 or stereo.

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post #10 of 12 Old 07-03-2013, 09:16 PM
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wait, this receiver was part of a dvd 5.1 combo and it doesn't support just plain dolby digital?
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post #11 of 12 Old 07-03-2013, 09:31 PM
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Quote:
Originally Posted by MlNDBOMB View Post

wait, this receiver was part of a dvd 5.1 combo and it doesn't support just plain dolby digital?

There is a bunch of them like this. Dolby Digital only when using the built in DVD player

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post #12 of 12 Old 07-03-2013, 09:40 PM - Thread Starter
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You're right Andy!
Bypassing the projector leads to way superior results! (ok, I had to solder a 3.5mm to double RCA, as the other one was passed to the ceiling...)

I do get something to the surrounds now biggrin.gif
The C/L/R speakers are also louder (leading to the surrounds being somewhat low)
The surround isn't as great as what I get from the DVD player, but at least there's audio all around.

I guess this will suffice until I decide to upgrade. Thanks a lot!

Mindbomb... yeah. kinda sucks. I tought there was a coax SPDIF input. turns out its an output. go figure.
Nevertheless, the surround I get from the XBOX is quite interesting.



If anyone is interested (likely to pop in search engines in months and might help someone else out?)

I configured the audio output as stereo speakers; but in XBMC I selected analog 5.1, connected directly from the motherboard's speaker jack to the curtis AUX input.
I seem to have good audio result too in winDVD running dolby pro logic II

But the best result are from the HDMI digital source converted to R/L input by the projector, not via HTPC

-Mars
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