Dolby Headphone Wrapper DSP, foo_dsp_dolbyhp Options

[Chungalin]

I'd like to introduce a DSP I've been developing these weeks. It's a Dolby Headphone wrapper DSP.

After some research on Lake DOLBYHPH.DLL bundled with software DVD players, I was able to find out its protocol used to interface with the client app. Then, why not make it work for myself?! And that was how foo_dsp_dolbyhp was originated. It wraps the functionality of the original DLL to be used under foobar2000. You just need to configure the plugin pointing out the location of that DLL in your system. Of course I'll NOT give any help about how to get that DLL.

foo_dsp_dolbyhp is available at the usual 3rd party component website. Any comments, criticisms, bug reports and legal issues are welcome (under this thread).

[pro_optimizer]

Can it really? After all you only have two channels as input (2.0 -> 5.1 with the PL2 plugin) and two channels as output (5.1 -> 2.0 with the DHP plugin). How can you have something "behind you" if there is neither "behind"-information in the source material nor any physical "behind"-information in the two output channels?

Yes, it can. If the source is encoded in Dolby Stereo (which exist since ~1970).
For each sound source you determine where it is, relative to the listener, along 2 major axes:
left <-> right and center <-> rear. Then, it's encoded like this (taken from wikipedia):
Left Total = Left*1.000 + Right*0.000 + Center*0.707 + RearLeft*j*0.8165 + RearRight*j*0.5774
Right Total = Left*0.000 + Right*1.000 + Center*0.707 + RearLeft*k*0.5774 + RearRight*k*0.8165
j = + 90º phase-shift , k = - 90º phase-shift

Its hard to get the original directions back from Left Total / Right Total, but its possible (with some assumptions such as relative stability of locations/frequencies over time and limited number of separable sources - probably up to 4).

This is your "behind" information in the source.

So where is the behind information in the output? Well, how can you determine if anything is behind you if your brain gets only two streams of audio (left ear+right ear)?
It can do this *only* because the sound coming from behind you sounds differently from sound coming from infront of you. That works because sound either gets blocked or reflected by your earlobes.
Cut them off and you loose your spatial information. This difference can be recorded and reproduced electronically. Listen to the samples at http://binaural.jimtreats.com/

This is your "behind" information in the output.

It would be great if you could make as most settings available to the user as possible. That way one would be able to tweak the plugin for an optimal use. After all I believe that a professional upmixing algorithm like Dolby Pro Logic II has to have some advantages over mere channel doubling. But at the current state of the plugin I cannot say that I really like the sound it produces.

Yeah, I'd like to add a separate volume control for each channel (I think this would be the most important thing - if no other plugin like channel mixer can do this), but doing all this GUI c*** is what I hate most about software development and I need a bit free time for that.
The second possible option is "music mode" versus "movie mode". Its in music mode by default, b/c movie mode makes not much sense within a music player, I think.
And I believe that this implementation doesn't have any more advanced options like "center width" and "dimension" like some more expensive A/V receivers have.
If you find any software player that supports this in its PL2 implementation then tell me please (I'm interested).

I've tested a bunch of songs up till now, and PL2 has won none of them. 4 chan -> DHP has won most, and no DSP has won a few. It's not up to loudness or extra bass, I can assure you. But I also made a test where I RG gained a FLAC file, then outputted each file with the different DSP, then RG'd those, and then tested them. I'm not disappointed in the surround aspect or the soundstage---it reminds me a bit of listening to my 5.1 system. However, it feels like I have my ears in tubes and there are speakers in the end of those; the music has this weird tinny feeling to it, I'll post samples if this doesn't make sense.

I believe you, although I cannot second that in general. But I'd definitely like to hear a few of those samples.
I found some stuff that sounds equally good, e.g. Dover, Coldplay, some others.
And some cinematic soundtracks like Once Upon A Time In Mexico (especially) or Gladiator seem to sound better with DPL2.

But I think I have understood what you mean by tinny. Since I use PL2 in exactly the same way as the Program that ships the DLL I suspect that this is an inherent problem of the combination of DPL2 and the virtual speakers present in Dolby Headphone. I am confident that I can solve that by equalization, though.

Christian

[Hancoque]

Okay, I think you're right about the "behind" information. But how often do you encounter music that contains an embedded surround signal? Isn't most music on a CD saved in plain stereo?