Frequency splits

[icecycle66]

I may have asked this before, I can't remember or find.

Is there a frequency splitter or notch filter sor of thing that will take everything above say 5000k and send it down one path and averything below that and send it down another path?

I don't want to eliminate the frequencies, I just want to break into multiple signal paths that can be indipendantly manipulated and recombined later.

[midwayfair]

See Bengt's Blue Monster for an example. Also any of the numerous harmonic tremolos. All you're doing is using a high-pass filer and low pass filter with their corner frequency at x, and then you can buffer/amplify them separately and do what you like from there. The calculation is 1/Tau*r*c, or just use a calculator like me: http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

Keep in mind that "splitting a frequency" is ... well, not perfect to put it mildly. A single pole filter is only 6dB per octave. If you make a low-pass filter with its -3dB cutoff at 5000KHz, you'll also have a -9dB cutoff at 2500Hz. That's not really that much quieter. It'll be down only 15dB at 1250Hz.

You can make a filter more steep by increasing the number of poles in a filter. Two poles is 12dB/octave. Three poles is 18dB/octave. Your DAW probably has a pretty good one that can get all the way up to 8 poles! You get more poles by adding more filters one after another. You can see an example of a three-pole filter in most choruses. Take a look at the output pin of the 3007 in the Pork Barrel -- the resistor/capacitor networks that follow are a 3-pole low-pass filter, meant to very steeply roll off the treble at a certain point while rolling it off less steeply below that point.

There are digital chips that can create an 8 pole filter. That's incredibly steep -- 48dB per octave -- and the closest you can come to actually putting a wall up for a frequency in analog circuitry. You need a clock driver and a 5V regulator to use them, though, so they're a bit unfun to use in most audio projects. However, Ray Ring (Circuit Salad) has a delay that uses an 8 pole chip. They're also expensive (about $5 each).

To get anything better than that, I imagine you'd actually need some sort of digital method of sensing when a frequency actually exceeds 5KHz and then it opens a gate.

Oh ... and remember that your guitar has high frequency content up that high even if it's not as prominent as the other stuff you're hearing. So you can easily make something happen when you don't want it to.