Filter Design - Calculate and display the impulse response (kernel) and frequency response for a windowed-sinc FIR filter - firkernel.htm

Why?

1. to better understand how filters work. Much of what I understand about filters I learned from The Scientist and Engineer's Guide to Digital Signal Processing. I recommend it.
2. to create FIR (Finite Impulse Response) filter kernels that I can copy and paste into BasicDSP (which has a FIR function), "A program for experimenting with simple audio DSP algorithms". I found BasicDSP by Googling PA3FWM, the author of WebSDR. PA3FWM (Pieter-Tjerk de Boer) is also one of the two authors of BasicDSP. (WebSDR is "a Software-Defined Radio receiver connected to the internet, allowing many listeners to listen and tune it simultaneously." WebSDR illuminates the use of a filter to extract a signal from the ether.
3. I have a long-standing interest (dare I say obsession) with DTMF - Dual-Tone Multi-Frequency signally. I've used filters I designed with this page in BasicDSP to create a system that separates the low and high frequency bands used in DTMF.

Notes

• When you design a filter with this page you get (in addition to the kernel and frequency response) a URL that will get your design back.
• The JavaScript in this page is heavily commented, with references to the DSP book, to explain how it works. The source is available as a Google Docs document. (The browser on my Palm doesn't have View/Source.) - http://docs.google.com/Doc?id=accnfh3pfb3_361g77gvbdn&hl=en
• Other pages I've found helpful in understanding filters:
  • Paul Falstad's Digital Filters Applet - It allows you to play with many different types of filters. It graphically demonstrates the relationship between the impulse response and frequency response, but it doesn't make available the impulse response (kernel) coefficients. - http://www.falstad.com/dfilter/
  • MAXIM's A Filter Primer - More than any other source it helped me understand poles and zeros and their effect on ripple in Buttterworth and Chebychev filter design. http://www.maxim-ic.com/appnotes.cfm/appnote_number/733
  • Quick Filter Technologies offers a series of FIR intergrated circuits. Since their entire business is based on FIR filters their website has a lot of information about them, including a free Microsoft Windows FIR filter design download that I discovered after I started working on this page. http://quickfiltertech.com/ | http://www.quickfiltertech.com/html/content_page.php?content_id=33&
  • http://del.icio.us/mshook/filter or http://mshook.googlepages.com/d4m.htm?/mshook/filter
• I used FLOT to create the graphs. I found it made creating attractive graphs very easy. FLOT, in turn, uses jQuery.
• Comments or questions: mshook@gmail.com

Tags: dsp filter javascript fir