Doom9's Forum - View Single Post - Dolby Pro Logic II encoding test (90° vs 180° phase shift)

ursamtl · 9th June 2006, 13:39

If you have Plogue Bidule, why don't you just model the Dolby encoding using it? Bidule has a built-in Hilbert Transform filter (although in my experiments, it seems to produce a -90° phase shift, so for the +90° shift, you'll need to invert the signal). Another option for the Hilbert is to use Christian Budde's excellent Phasebug VST plugin (freeware). This gives you the possibility of any phase shift in a 360° circle.

If you don't have Plogue Bidule, try Audomulch.

I haven't done much with DPLII since I've never been impressed with its results, but I can tell you that in my experiments with Ambisonics, the 90° phase shift used in some encoding designs is essential. For example, in the superstereo circuits I've modelled using Plogue Bidule and Phasebug, the 90° phase shift balances the ambience nicely across the surround speakers, but moving it to 0° or 180° forces the ambience all to one surround speaker on another. Again, the application is different from DPL, but I've read a lot of surround sound documentation over the past couple of years and the Hilbert Transform is everywhere!

Finally, I know you guys are passionate about your points of view, but let's relax and enjoy this experimentation.

Regards,
Steve.

9th June 2006, 13:39	#20 \| Link
ursamtl Registered User Join Date: May 2004 Location: Montreal Posts: 729	If you have Plogue Bidule, why don't you just model the Dolby encoding using it? Bidule has a built-in Hilbert Transform filter (although in my experiments, it seems to produce a -90° phase shift, so for the +90° shift, you'll need to invert the signal). Another option for the Hilbert is to use Christian Budde's excellent Phasebug VST plugin (freeware). This gives you the possibility of any phase shift in a 360° circle. If you don't have Plogue Bidule, try Audomulch. I haven't done much with DPLII since I've never been impressed with its results, but I can tell you that in my experiments with Ambisonics, the 90° phase shift used in some encoding designs is essential. For example, in the superstereo circuits I've modelled using Plogue Bidule and Phasebug, the 90° phase shift balances the ambience nicely across the surround speakers, but moving it to 0° or 180° forces the ambience all to one surround speaker on another. Again, the application is different from DPL, but I've read a lot of surround sound documentation over the past couple of years and the Hilbert Transform is everywhere! Finally, I know you guys are passionate about your points of view, but let's relax and enjoy this experimentation. Regards, Steve.