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Logic Low Pass and High Pass Filters- Affecting Phase/Mix?


gg333

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Hey guys. I've been producing for a long time but just realized something I've always done for convenience could potentially be causing mix problems. I've Googled it up and down and it seems to turn into a pretty technical debate regarding phase issues? It's hard to explain, unsure but maybe you can help shed some light:

 

Every song I've ever created and exported EVER- I use Logic 9's Legacy Low Pass and High Pass filters within Logic X. The Legacy ones because I don't like how they've changed the name to "Single Band EQ" with a low cut and high cut setting within it- it's much easier to see the legacy Low Pass And High Pass as separate plugins in the mixer. I keep these legacy filters turned ON all the time, but usually the frequency slider is at its max setting so it's not actually doing anything. At least it's not SUPPOSED to be doing anything. The reason for all this is simply automation convenience. When I want to automate a filter it's right there ready to go using the frequency slider. It makes workflow super fast this way.

 

I have these filters across nearly every channel and bus in my mix, INCLUDING the master channel. Again I didn't think it was doing ANYTHING leaving the plugin on but with the frequency slider at its max open position. However I started messing around with tests on the master channel and noticed the second I turn either plugin on, it causes a mastered song to slightly clip on a meter. Turn it off- and the song goes right back down. This got me thinking- if the filters being left on are clearly altering the gain, what else are they altering?

 

So of course I auditioned several test tones and A/Bd turning the filters on and off. With a sub bass test, I swear it is SLIGHTLY weaker when turning the low pass on vs. off. This should seem obvious being it's a low pass filter, but with the frequency all the way open at 20000Hz shouldn't it not be doing anything? After testing repeatedly now I can't tell if my ears are playing tricks on me.

 

In other threads and forums, some were saying that leaving ANY filter on immediately alters the phase of the sound and causes a slight Q "bump" at the cutoff point therefore what's responsible for the gain increase. These turned into huge debates so I couldn't get a definitive answer as to what's actually going on.

 

TLDR: For automation convenience is leaving Low Pass and High Pass filters "ON" but not actually filtering until needed, across my channels busses and master altering the sound/mix and/or causing phase changes?

 

Thank you all so much for your help on such a silly thing.

 

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