Pro Logic bass (1 Viewer)

[Hugh Scrivener]

While of course DTS or DD is the preferred format Many of my 'digital' cable channels broadcast a Dolby 2.0 signal, which I use traditional Pro Logic to decode into surround. I know the center channel is culled from the two front channels by taking the shared information from each channel and matrix's it into the center, leaving the uncommon info to each respective front. And I know the rear channels are derived from the fronts through some out of phase voodoo that I'm not sure I completely understand. But where does the bass track(sub-woofer) come from? I'm sure its a set crossover in the decoding that sends low freqs to the woof, but what is that freq?
With the cheap sub I have...won't mention any names(mainly from embarrassment), it rhymes with yolk...oops..I slipped, Ican't really handle some of the lower freqs found in DTS or DD without turning the woofer WAY down..of course losing the original impact of the flick. But with music and Pro Logic decoding its not so bad. I figured if I could set the x-over as close to the PL standard as possible I might get better over-all response from the shoe box in the corner.
Or am I totally whacked in the head? I'd still, just for curiosities sake, like to know.

 

[Chris Brown]

Standard Pro-Logic provides for four channel reproduction (4.0). This includes Right Front, Left Front, Center, and Rear Surround (although 2 speakers are often used, they are producing the same sound). There is no dedicated LFE/Bass channel.
Pro-Logic II provides for 6 channel reproduction (5.1). This includes Right Front, Right Left, Center, Right surround, Left surround, LFE (Bass)
If you are using the regular Pro-Logic, there is no bass separation done in the decoding, however your receiver may still be able to send bass to your subwoofer via your crossover. (When you have your speakers set to small and it redirects the bass to the subwoofer). On my old Pro-Logic receiver I simply had the sub getting the signal from my mains and then using the onboard crossover to filter the signal.

 

[NickSo]

Yeah, the bass on ProLogic1 was horrible... I got a makeshift fix by adding a car subwoofer crossover that had a bassboost. I rigged it so it got power off a 12v AC/DC adaptor rather than from the car. Whenever i wanted more bass, i just flick the switch for bassboost, and i got it. Not the most elegant way, but it works...

 

[Lewis Besze]

Hugh,
Dolby Surround goes like this in a simplistic way:
Center= L+R [mono sum]
Surround= L-R,then reversed to out of phase[kinda like Hafler "surround"]
There is no "LFE" as others ponted out,the bass is in the full range mains as well,however the surrounds are limited by design from 100hz-7khz.

 

[Hugh Scrivener]

If you are using the regular Pro-Logic, there is no bass separation done in the decoding, however your receiver may still be able to send bass to your subwoofer via your crossover. (When you have your speakers set to small and it redirects the bass to the subwoofer

I have to dispute the 'small' setting procedure on the amp. I keep my speakers set to large, in order to take advantage of the full range signal 5.1 provides, sending only LFE to the woofer. and I get ample bass from the sub in PL. IMO this is the way it should be...the endless debate.. all channels in a movie soundtrack are recorded with a certain amount of bass, the LFE channel is for just that, LOW frequency effects. Mains and surrounds DO have bass info and the sub is there to carry the truly low bass. A theater gets away with using smaller surrounds(along the side walls) because they typically have 10 or more subs hidden in the room, often 15 or 18 inches in diameter producing ample bass for all channels. again,IMO, to send all bass to the sub produces a muddy sound form the sub as it it one speaker trying to produce all the channels at once. Try leaving the sub set to on in the amp, and un hooking or turning the sub off, I believe you'll find bass being produced by the mains(if set to large)but not the true LOW bass. This is mostly bass from the music soundtrack and other incidental bass, NOT LFE. My understanding is thats what the sub is for...LFE(explosions, Jango Fetts death charges, etc.) I was just wondering aloud...and oh BTW where does the bass info come from in PLII?

 

[Lewis Besze]

all channels in a movie soundtrack are recorded with a certain amount of bass, the LFE channel is for just that, LOW frequency effects.

Actualy there are quiet a few tracks when the mains and center gets equally low amount of bass, with amplitude to match.