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Linear Phase EQ shootout!!! Equalizer Plugins
Old 29th July 2010
  #31
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Quote:
Originally Posted by DaveGamble View Post
What does the spectrum of the nulled signal look like?
If you see a lump at/around 500hz, it indicates that your settings were incorrect; grab an analyser and verify that you get -6dB at 500Hz from both filters; with 24db/oct this should work out correct. Also, you'll need a Q of 0.707, using the standard definition. Plausibly the EQ designer might normalise this to 1. I've seen weirder things.
Also, make sure you test on a static signal! :P

Dave.
The settings are definitely good, and identical. The spectrum shows a lump at 500 Hz down about -132 dB. Using 24db/oct the residual signal is down at around -53 dB. When I try this with other LP's, for example my DAW's LP EQ, I get down to -163 dB thereabouts.
Old 29th July 2010
  #32
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Notice that a linear-phase filter has to be made with some compromises and the differences may well be bigger than between minimum-phase EQs. For example Algorithmix Red and Orange are both linear phase.

Technically:
A minimum-phase filter has (theoretically) infinite post-ringing. A perfect linear-phase filter requires infinite pre-ringing, but in real world you can only have a limited latency. Some linear-phase EQs let you choose this latency, some don't.
Old 30th July 2010
  #33
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Quote:
Originally Posted by TranscendingM View Post
The settings are definitely good, and identical. The spectrum shows a lump at 500 Hz down about -132 dB. Using 24db/oct the residual signal is down at around -53 dB. When I try this with other LP's, for example my DAW's LP EQ, I get down to -163 dB thereabouts.
Try sweeping one of the frequencies around and see if you can do anything that improves the -53dB figure. Might be that the filters are normalised so that you always have -3dB at the cutoff frequency, rather than -6dB.
Old 30th July 2010
  #34
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Quote:
Originally Posted by jdtrbn View Post
Notice that a linear-phase filter has to be made with some compromises and the differences may well be bigger than between minimum-phase EQs. For example Algorithmix Red and Orange are both linear phase.

Technically:
A minimum-phase filter has (theoretically) infinite post-ringing. A perfect linear-phase filter requires infinite pre-ringing, but in real world you can only have a limited latency. Some linear-phase EQs let you choose this latency, some don't.
Absolutely right, but the ringing does tail off pretty fast, particularly for something simple like a smooth 6dB shelf lift; to the extent that the window chosen (what we use to make the ringing behave) shouldn't have THAT much of a difference. If it was <-96dB of cancellation, I'd believe it was a windowing/response length matter; because that would indicate a bit of error in computing the response shapes, and that would really be believable. The >-30dB cancellation I was hearing (do try it yourself), and the fact that it sounds just like a phaser leads me to suspect that a repeat of the test would be informative.

Dave.
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