does anybody know of a filter or similar that can be used to attenuate low frequencies i.e. bass boost? trying to build a type of eq unit!

all help greatly appreciated

You want a low pass to boost bass, for example [lop~ 4000], then increase the gain a bit.

Filter terminology is sometimes confusing. Several terms are used to mean the *same thing*
Attenuate means to reduce or diminish, so a bass boost would be the opposite of attenuating low frequencies. However if we talk about a high pass filter, that's the same *effect* as a low cut filter. Removing highs has the same *effect* as increasing lows and vice versa. Because if you take away some bass and restore the signal to its original volume then you did the equivalent of boosting up some treble.

so, if =~= means "does about the same thing as"

high pass (boosts treble) =~= low cut (attenuates bass)

for that use [hip~]

low pass (boosts bass) =~= high cut (attenuates treble)

for that ise [lop~]

Top and bottom filters are usually taken to be "shelfs", meaning the high pass filter admits signals from its cutoff up to the highest possible frequency, all the way to the top. And conversely a low "shelf" allows through frequencies from its cutoff all the way to zero, all the way to the bottom.

Now, if you add a middle "band", between the top and bottom, it has two sides, what is above it and what is below it. So a "mid cut" is the same as boosting up the bass and treble, and a mid boost is the same as cutting the bass and treble.

for that use [bp~], the band pass

So how do you set the top and bottom limits of the band pass? You don't. Instead you set the middle frequency of the band and the width of the band. An EQ filter shouldn't be resonant, and so the last parameter of [bp~] should be 1

Because it gets a pain in the ass to work out the center frequency and bandwidth of [bp~], [hip~] and [lop~] filters you might like to look at [hml_shelf~], [bpw2~] and some others in iem_lib that are better designed for building EQs

thanks a lot, I just about worked out the hp~/lop~ bit myself and using triggers got it doing what i want. your advice for building all three was most useful.

thanks