# Logarithmic Interpolation of Hard Knee Curve



## Nordo (Feb 28, 2008)

My understanding of Logarithmic Interpolation is that you now only have to enter the start and end of your straight section of curve (say 30 6.0; and 0 80.0), and the interpolation will plot a straight line for you on the horizontal logarithmic scale.

Well, I can't get it to do that. I can definitely get a straight line by using my own 8 or 10 coordinates, and no interpolation. But not using two end points and interpolation.

What am I missing?:scratchhead:


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## hasse_swe (Jan 6, 2008)

Nordo said:


> My understanding of Logarithmic Interpolation is that you now only have to enter the start and end of your straight section of curve (say 30 6.0; and 0 80.0), and the interpolation will plot a straight line for you on the horizontal logarithmic scale.
> 
> Well, I can't get it to do that. I can definitely get a straight line by using my own 8 or 10 coordinates, and no interpolation. But not using two end points and interpolation.
> 
> What am I missing?:scratchhead:


set speaker type to "full range" and see what happens!.. 
/H


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## Nordo (Feb 28, 2008)

OK, I can see what happens to the "curve", but WHY?:scratchhead:


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## hasse_swe (Jan 6, 2008)

Nordo said:


> OK, I can see what happens to the "curve", but WHY?:scratchhead:


i'm also a little confused about that part...:whistling: 
but it's something with combined curves (i think) so when u use set speaker type to subwoofer..
all curves are combined...target/cross over curve+house curve..
something like explained in post:
http://www.hometheatershack.com/forums/rew-forum/2362-target-response-house-curve.html#post16401

or maybe some pros can explain why it's necessary to use combined curves instead of simply use house curve and nothing else?....:huh:


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## brucek (Apr 11, 2006)

> why it's necessary to use combined curves instead of simply use house curve and nothing else?....


I honestly have no idea what this means?


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## plundstrom (Nov 5, 2007)

hasse_swe said:


> why it's necessary to use combined curves instead of simply use house curve and nothing else?....:huh:


End result what you are after is that sub + mains should follow your "hard knee house curve". So when setting just a sub it has to follow sub low pass filter + hard knee and there target line can't be straight. It has to have some bending. Once you get your sub to follow this "not so straight line" and you connect your mains (that will follow high pass filter also not so straight line) the combined result will be straight hard knee curve, just what you wanted.

Repeat; sub alone won't produce straight looking line. Same goes to mains also. But when both are enabled math miracle happens and you get your straight hard knee curve. :jump:


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## brucek (Apr 11, 2006)

> OK, I can see what happens to the "curve", but WHY?





> i'm also a little confused about that part


You fellas are making this far more difficult than it needs to be.

Here's the skinny:

Some people like the sound of the bass a bit exagerrated at low frequencies instead of following the standard subwoofer target that REW offers.

REW software was modified to allow you to add a couple data points into a file (called a house curve file) that would result in the bass boost to the target line (that REW uses to create its suggested filters).

Many people noticed that when you draw a line between two points on a logarithmic graph, the line ain't straight, it's humped.

The REW software was modified so that the line drawn between the two points is now straight (if desired). It's called logarithmic interpolation.

brucek


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## hasse_swe (Jan 6, 2008)

aha...oki thanks för the explanation guys!..:T
now things are a bit clearer... :yes:


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## Nordo (Feb 28, 2008)

brucek said:


> You fellas are making this far more difficult than it needs to be.
> 
> Here's the skinny:
> 
> ...


Yes, but my original point is that with logarithmic interpolation ticked, the generated line between two points (when in sub mode), is *not* straight. The line is humped. To get the line to appear straight, I need around 10 coordinates.

I am using v4.11.


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## plundstrom (Nov 5, 2007)

Nordo said:


> Yes, but my original point is that with logarithmic interpolation ticked, the generated line between two points (when in sub mode), is *not* straight. The line is humped. To get the line to appear straight, I need around 10 coordinates.
> I am using v4.11.


You need to read this thread again. It's been explained. To get straight line you don't need more than 2 points when using logarithmic interpolation.


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## brucek (Apr 11, 2006)

> the generated line between two points (when in sub mode), is not straight


Yeah, I suppose it's not perfectly straight. The shorter the line, the less the effect. It simply removes the exaggerated hump. If you don't like it, just use a bunch of points. No problem. It's simply not going to make much difference in the sound....

brucek


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