Plotting R B-J Equalisers in Excel

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