Simple high pass filter question
- Thread starter Locrian99
- Start date
Cybercow
Well-known member
I don't think so. RL is the load impedance and RIN is the input impedance. Should be about 16K for RB and 100nF for C1. But that only renders a -3db slope. To get a -6db slope, you would need two of those HPFs in series.
DigiKey LPF & HPF Calculator
DigiKey LPF & HPF Calculator
Rin and RL depend on the impedance of whatever is before and after. Ideally you assume 0 for Rin if a buffer or active pedal (with low outpu impedance) is before it, and 1M for RL, as most pedals and amps have 470k~1M input impedace. But, if you're putting this first in chain (connected directly to the pickups), then the output impedance of the pickups will make a big difference.
A lot of calculators ignore Rin and RL and just calculate the RC, assuming low Rin and high RL.
A first-order filter calculator like that will tell you the cutoff frequency where the output is -3db. You'd have to set the cutoff freqency higher that 90hz to get -6db reduction at 90hz.
A 2nd order filter will be steeper, and I believe the cutoff frequency from a calculator tool will be at -6db. The pedalpcb Frequency Interchanger uses 2nd order (or 2-pole) for the highpass filter (Sallen & Key style).
A lot of calculators ignore Rin and RL and just calculate the RC, assuming low Rin and high RL.
A first-order filter calculator like that will tell you the cutoff frequency where the output is -3db. You'd have to set the cutoff freqency higher that 90hz to get -6db reduction at 90hz.
A 2nd order filter will be steeper, and I believe the cutoff frequency from a calculator tool will be at -6db. The pedalpcb Frequency Interchanger uses 2nd order (or 2-pole) for the highpass filter (Sallen & Key style).
Locrian99
Well-known member
This is the tone stack calculator i was using to find where -6 at 90hz was
Yet Another Tonestack Calculator
Guitar amp and pedal tonestack (tone stack) calculator web app. Tweak controls and component values and compare frequency responses in real time. Inspired by TSC in the web and Duncan Amps TSC.
tonestack.yuriturov.com
pricklyrobot
Well-known member
This is a really good video series on filter basics:
It’s from a synthesizer perspective, but it mostly all still applies to pedals.
He goes from passive filters all the way through to active resonant filters with CV control.
It’s really easy to follow, and you can just stop whenever you get to the level of filter complexity you’re looking for
He goes from passive filters all the way through to active resonant filters with CV control.
It’s really easy to follow, and you can just stop whenever you get to the level of filter complexity you’re looking for
