madbeanpedals::forum

General => Open Discussion => Topic started by: icecycle66 on August 10, 2012, 08:35:49 PM

Title: Frequency filter measuring
Post by: icecycle66 on August 10, 2012, 08:35:49 PM
How can I measure the frequency sweep/point of a filter?
Such as the one on the Boss Bass Chorus (CEB3).
Title: Re: Frequency filter measuring
Post by: culturejam on August 10, 2012, 11:47:03 PM
There is a very basic formula for determining the cutoff frequency of a given filter type. I'm assuming you are talking about R/C filters (resistive/capacitive).

Here's the equation:
(http://sim.okawa-denshi.jp/images/CRLowfc.gif)

I use an Excel sheet with the equation applied, so all I have to do is punch in the numbers for the resistor and capacitor.

But you can also use online calculators. I use Excel because sometimes I want to show several different sets of values at the same time. This is handy for dialing in a tone control, as you can see how the cutoff frequency changes as the pot is turned.
Title: Re: Frequency filter measuring
Post by: pickdropper on August 11, 2012, 02:18:37 PM
CJ is right on with the calculations.

If you are looking to do real time measurements, there are a number of options.  There is an FFT Spectrum Analyzer program called Spectra Plus that would allow you to do it.  It is somewhat pricey if you get all the options, but you can download the full version for 30 days to try it out.

http://www.spectraplus.com/ (http://www.spectraplus.com/)

There are other, cheaper options (TrueRTA, I believe), but I don't use them.
Title: Re: Frequency filter measuring
Post by: icecycle66 on August 11, 2012, 06:49:03 PM
Wow, thanks guys.