Question about filters

K

kisolee

New member
I've noticed there are filters that are named like '6db/octave' (1-pole), and '12 db/octave' (2-pole). And I tried to research a little bit about filters, and found that 2-pole to 4-pole filters are like stacks of 6 db/octave filters working together. Can someone explain to me a little more in-depth about filters? Why are they connotated as 6, 12, and even 24 db/octave? What's the difference between them?

Thanks
 
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When you high pass something
it means you dont want the frequencies of that sound below that frequency
So everything above passes,
Everything below gets cut/ducked/removed

For example you may want to high pass the kick drum to the 60 hz

But you dont want like an aggressive remove of the frequencies below that so you adjust how much db for octave you want to duck
You may have different approach to different sound how you high pass them, or low pass them

And thats all about it
 
6db, 12db, etc describe how the filter reacts to frequencies above/below the filter's cutoff frequency. So, for every octave above/below (depending on whether it's HP or LP) the cutoff, a a 6db filter lowers the output by, well, 6db, not an uncommon setting for use during mixdown. Sharper cutoffs (12db, 24db) are more often used with synths for that filter sweep "waaooowww" sound.
 
I'm sure you've noticed if you use a lowpass filter that they don't actually remove everything above the cutoff- it's just that the filter starts filtering at the cutoff and you have to up a few notes before it totally dies away.

The 12 dB per octave is literally how fast the filter removes those frequencies past the cutoff- if you're one octave above the cutoff of a 12 dB per octave lowpass filter then that frequency will be 12 dB quieter than without the filter. If you're two octaves up, then the filter will make it 24 dB quieter, which is pretty low volume.

I hope that helps- feel free to ask more questions.
 
I found this thread extremely enlightening. I never thought about the diff. Db's referring to the steepness of the cutoff. Thanks
 
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