Does anyone have the surround delay formula? (1 Viewer)

[VicQ]

My receiver doesn't automatically adjusts the surround delay as newer receivers do. The default delay right now is 20ms for dolby prologic and 5ms for dolby digital and dts. After almost 3 years I decided to play around with the delay and noticed that the soundfield cohesion and front to back and back to front panning is much better if I reduce the delay. My fronts are about 12 ft away and the surrounds are up and to the sides of the listening position about 6 ft away. I was under impression that you delay 1ms for every feet, but since that's about how I had it set up for the last couple of years, I always noticed that the sond seemed to jump when front to back panning was present. Now that I'ved reduced the delay, this is not the case. I know there's a correct formula somewhere. Any help?
-Vic

 

[stephen abbot]

Vic, you are quite correct, 1mS equates to 300mm or approx 1ft.
To get the exact fiqure you should measure from the face of the speaker to your head when sitting in the listening position, this will require help from your assistant.
So to sum up, you must measure the direct flight distance from the Front speaker face to your head, and substract the direct flight distance from the Rear speaker face to your head. The difference in feet is the number of mS you should enter for DD/DTS, ProLogic is recommended to have a delay 15mS greater than the absolute delay calulated above.
This natuarally assumes the left/right Front distance to sitting position is equal, and as with the rear, obviously a symetric layout will always give best results.
Cheers
Stephen.

 

[Wayne A. Pflughaupt]

Vic,
First,
Welcome to the Forum!
The delay setting is critical with Dolby Pro Logic. Since the rear surround channel is matrixed and not a true discrete channel, the delayed signal helps improve separation between the front and surround channel.
As I remember from the magazines I used to read regularly back when DPL was the main standard, the delay setting should be calculated at 10ms. That figure should be added to the difference in distance to the seating location between your front and rear speakers. In your case, the rears are 6 ft. closer than the fronts, so the correct delay setting would be 16ms.
Delay is less critical for Dolby Digital, since there is a true discrete channel and the delay is not needed to “fake it.” However, typically a little delay is used.
Cheers,
Wayne A. Pflughaupt
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[VicQ]

thanks to all who have replied so far. After I started experimenting, I had the setting for Dolby prologic at 17ms, and this automatically adjusts Dolby digital to 2ms delay. I tested U751 and when torpedoes panned front to back, the sound happened too quickly, thus you didn't get the sound to stay too long on the surrounds. I now have it at 18ms and this puts DD at 3ms. I tested it with A Bug's life and front to back panning sound was satisfying enough. I will have to do more testing. The problem is that my couch is flushed right against the back wall, with the surrounds up high and to the side. I'm not sure if this has some sort of effect as far as the sound arriving to my ears and causing the formula not to be as accurate as it should be.
-Vic