# Rear fill Pro's and possiblities



## savagebee (Sep 12, 2006)

This is not my work, this is stuff from the big poll thread.

Seems as though it has gotten sooo long that people are not reading through it anymore, so i figured I would compile a lot of the ways to make it work well

I have quoted the people who said this stuff in all cases 



werewolf said:


> "rear fill" encompasses many possibilities :
> 
> - simple, attenuated L and R
> - delayed (beyond Precedence, or Haas, Effect), attenuated, bandlimited L and R
> ...





werewolf said:


> Your friend isn't the only one who thinks you can get surround from a 2-channel signal
> 
> Dolby Pro Logic II, DTS neo:6, Harman Logic7 come to mind ...
> 
> Sure, they have more sophisticated steering algorithms ... but have you heard a well-tuned system using a delayed, bandlimited L-R difference signal sent to the rears?





werewolf said:


> Big difference between a concert hall and car: size of the acoustic space!
> 
> And it's NOT just a relative difference ... there's a real, tangible _threshold_ involved, as defined by the Haas Effect. In a car, there's a real good chance that the natural reflections will _not_ exceed the precedence effect (about 20msec, if memory serves) ... meaning that natural reflections will only tend to smear and confuse the front stage. In a concert hall, there's a real good chance that the natural reflections _will_ exceed the precedence threshold.
> 
> ...





Preacher said:


> I don't think you'd have to "voice Match" front and rear. in a concert hall the reflections are so different from the initial sound. That's what gives each room its own distinct character. I'd try various cheap small mids -
> 
> Madisound Store
> Several of the Goldwoods come to mind.
> ...





werewolf said:


> The "L-R difference" signal is really just that : the algebraic _difference_ between the left and right signals. Sometimes it's called the "ambience" or "surround" component of the original 2-channel source.
> 
> Consider a _largely_ mono signal, like voice (in most recordings, certainly not all). A mono signal will have about the same level in the left and right channels ... and will therefore _disappear_ in the difference  So immediately we recognize a HUGE difference bewteen standard, L and R rear-fill and a rear-fill signal constructed from the L-R difference : one will have the main vocal in the rear, the other will not  Perhaps that alone is a big incentive to resist lumping _all_ rear-fill possibilities together?
> 
> Anyway, check the link i posted earlier for more about L-R difference signals, and how to construct and manipulate them _without_ using PL II, Neo:6 or Logic7.


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## savagebee (Sep 12, 2006)

MiloX said:


> He's not being fancy for stereo. You should read it as an equation:
> 
> (L signal)-(Right signal)=Difference Signal
> 
> Or to put it another way: The end state signal is the delta between the Left and Right signals.





werewolf said:


> If you get a chance, delay them beyond the Haas Effect (Precedence Effect, about 15~20 msec), maybe even play with L-R difference ... a whole new world will open up to you, beyond simple (attenuated) rear fill





thehatedguy said:


> Yeah, but you DO get ambient reflections off of the back wall. That stuff ads to the feeling of the size and space of the room.





werewolf said:


> If the signal is appropriately delayed (at or beyond Haas), the rear will _not_ pull the stage back. Furthermore ... if differenced (L-R), bandlimited and appropriately attenuated, we open up a whole new category of "rear fill" ... the ability to create a much larger acoustic space  However, _this_ type of "rear fill" will _not_ be particularly friendly to rear-seat passengers





werewolf said:


> i'm referring to every other post i made in this thread
> 
> ... and every other thread like it, where people always quickly jump on the "rear fill sucks!" bandwagon, often without even appreciating the world of differences in the _very different_ categories of rear fill.
> 
> ...





npdang said:


> I've tried duplicating what was mentioned in the MLSSA article awhile back and found the results to be somewhat dissapointing given the extra investment in equipment (rear speakers, 2 extra channels of processing and amplification).
> 
> I think it may have to do with the excessive amount of EQ necessary to match corresponding front and rear speakers, or perhaps my method of signal steering wasn't sufficient for a car. I tried both wiring the rear speakers out of phase, and as suggested a time delay of 16ms and 24 ms... with the out of phase signal signal providing better decorrelation and ambiance.
> 
> I do have high hopes though for logic7 processing in JBL's upcoming ms-8, as I've seen a few comments regarding how it was specifically designed for cars.





werewolf said:


> The first thing you have to understand is how a "balanced input" works. A balanced input on a preamp or processor is different than an RCA (single-ended or unbalanced) input, in that the balanced input is NOT "expecting" one of the input conductors to be at ground (or close) potential. An RCA input, on the other hand, is "expecting" the ring or shield input to be at ground ... in other words, no signal.
> 
> This needs to be clear first, if not ... let me know.
> 
> ...





> Whiterabbit said:
> 
> 
> > so to paraphrase/confirm, to be able to INDEPENDANTLY process the left and right channels, I need either:
> ...


more below


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## savagebee (Sep 12, 2006)

Whiterabbit said:


> to my knowledge, the opposite. a bridged amp will sum the input signals. By inverting one signal, the summation will result in an L-R (as in, L + (-R)) signal. This would be run as a bridged output to a rear speaker.
> 
> By running the two rear speakers in series, they both get this L-R signal.
> 
> ...


more later
I have Work all the sudden


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## DanMan (Jul 18, 2008)

I, for one, appreciate the work you're putting into this. You are right, the original thread is way long.

Spoonfeed me, please


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## savagebee (Sep 12, 2006)

Abmolech said:


> Draw a grid map.
> 
> Place an equilateral triangle of suitable size over the grid.
> 
> ...





sqshoestring said:


> I posted some of this before but I'll try to narrow it down if you are thinking of rears.
> 
> To put it simply the reason I run rears is because the left channel (I'm driving) is so close to me it seems way forward of me...in essence it is mono. But if I run rears the right way they can pull that channel back to me so the left is left, not forward. The more distant channel is not as affected since both rear and front are to the side anyway. This way I get the stereo separation/crosstalk/image I find in headphones or a proper home setup. IMO I get all the center I need from reflection in a car, or whatever the reason is I rarely get as much separation in a car as in home. I can fade the rears in and hear the stage expand right out.
> 
> ...





Hi There said:


> I've done some experimetation with BW L/R difference (defeating the HAAS effect with delay actually occurred to me before I knew exactly what PLII and the like did). In my mind, a stereo CD as a source is just that -- a stereo source. Ambiance is, if the recording engineers see it as necessary, ecoded on the CD with playback on a 2.0 stereo in mind. Some music (a lot of Tool comes to mind) varies between being intentionally claustrophobic to widely staged and "big" sounding. To me, efforts at rear fill with delay involved is analagous to putting a great stereo system in a simulated theater...does it "improve" the original recording? Does the recording need improvement due to the limitations of the car listening environment?
> 
> I think the best medicine for a stereo source in a car situation, is use of deadening to defeat artificial reflections, and reliance upon the encoded material on the CD to create ambiance. There is, imho, no allowance for end-user listening space reflections and such on a good stereo recording (I think they engineer or at least should engineer assuming nothing about the listening space as a factor), so why would I create the effect of one particular space and apply it to all my recordings? Most of us rail against use of volume limiting and such, and engineering for an ipod world...why would we think otherwise of artificially creating an ampitheater of our listening space, when we can assume nothing of the sort with regard to the intention of the source material?
> 
> But as with all such "processed" effects, I have to say that it could be material and personal preference dependent. Suffice it to say that there are large and obvious problems with stereo in general, and that these are only increased in a car environment....I think rear fill can be a solution to some of these, but it paints with too broad a brush for my liking.





VP Electricity said:


> Taste and preference are different.
> 
> Stereo by definition has a solid image in the recording. It is already defined - we don't get to argue about that.
> 
> ...


.....


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## savagebee (Sep 12, 2006)

Now there is tons of other extremely good comments and debates within the original thread, located here:http://www.diymobileaudio.com/forum/product-selection-comparisons/9806-rear-fill-do-you-use.html

but this seemed to be the core of the pro rear fill arguements.

Time aligned, limited bandwith, and l-r signal. I plan on trying this if i up my processing power, and I use the thread as a reference, this way, others can do the same


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## iregret (Jul 27, 2009)

I appreciate you doing this. Good job.


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## mitchyz250f (May 14, 2005)

Nice work


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## Builtlikeatank (Sep 22, 2008)

Wow, some very interesting points in here...may have to rethink this whole thing...


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## jasondplacetobe (Jun 15, 2009)

thanks for the compalation. iam gonna give it a basic try and see if i want to go further.


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## mitchyz250f (May 14, 2005)

Great summary, I keep coming back to this over and over again.

thanks.


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