**References :** Posted by Web Surf

**Linked file** : rbj_eq.xls

**Notes :**

Interactive XL sheet that shows frequency response of the R B-K high pass/low pass, Peaking and Shelf filters

Useful if --

--You want to validate your implementation against mine

--You want to convert given Biquad coefficients into Fo/Q/dBgain by visual curve fitting.

--You want the Coefficients to implement a particular fixed filter

-- Educational aid

Many thanks to R B-J for his personal support !!

Web Surf WebsurffATgmailDOTcom

**Code :**

see attached file

**Comments**

__from__ : Paul_Sernine75[AT]hotmail[DOT]fr

__comment__ : It also works perfectly with the openoffice2.02 suite :-)

__from__ : jackmattson att gmial

__comment__ : Ok, so I'm about to make my first filter so I really have no idea about coefficients yet but damn this is the coolest .xls I've ever seen! And I see a bunch every day. :?

__from__ : WebsurffATgmailDOTcom

__comment__ : Thanks,
It's just an implementation of the R B-J cookbook formulae for parametric equalisers. RB-J personally assisted me while I was writing this XLS. The real Kudos goes out to him !!
I wrote this as in intermediate tool while I was writing some Guitar effect DSP routines.
One prob it has : If the Q is too sharp, the peak filters have a very sharp tip. It is possible then as you slide the F sliders, that the chosen F is not one of the data points that I am plotting.
The net result is that the peak of a hi-Q filter seems to increase/decrease as you move F. This is a shortcoming of the way I programmed my XLS and is not a problem with the R B-J equations.
PS : I saw the same problem with other similar S/W on the net !!!
PS : Anyone know how to do curve fitting so that we enter in some points through which the frequency response must pass, and it generates best set of F,G,Q ?

__from__ : WebsurffATgmailDOTcom

__comment__ : Date: Sun, 17 Apr 2011 12:34:09
Subject: RBJ Filter Plotter Spreadsheet
From: Robert Bonini <XXXXXXXXXX@gmail.com>
To: websurff @ gmail . com
Just wanted to complement you on the good work. I came across your RBJ filter plotter spreadsheet, and it's quite good.
The version I have is dated Feb.2006, so this may have been addressed already but I did notice a small issue with the sample frequency input.
Anything other than 44.1 KHz would cause the response curves to peak at incorrect values on the x axis. The normalized frequency 'w' was
being referenced to 44100, and not to the Fs cell. I modified the formula to absolute reference B56 and it solved that problem.
Thanks for your great work,
-robert