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Old 2013-03-29, 19:24
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selig selig is offline
Join Date: Jun 2003
Posts: 10,489
Originally Posted by nickmorgan19457 View Post
James Bernard's Multiband Tool Box
Craziness like this is why I use Reason.
What he is describing is a "Phase Coherent" crossover filter network, where the high and low pass outputs are what is called "Phase Complementary". This is how the Stereo Imager works. If you look at just the low band or just the high band, you will see they are not "linear phase" filters in any stretch of the imagination! Both are as much as 90° or more out of phase at certain frequencies. In this pic showing phase, the LP is red, the HP is green, and the combined phase is in blue (crossover set at the default 787 Hz):

BUT, when they are combined, because of the fact that they are phase complementary, the results will be flat. Here is the magnitude response of each filter and the combined output - same colors as before:

I was speaking of linear phase FIR filter design, which is a different beast all together. :-)
Giles Reaves, aka 'selig'
Audio Illusionist, Musical Technologist
Selig Audio, LLC