IIR digital filter design applet
(Java 1.02 version)
- Note
- This page contains a Java 1.02 applet: it should
work with Netscape Navigator (version 2.0 or later) or Internet Explorer
3.0.
- If you are using Internet Explorer 4.0, or Netscape
Navigator 4.0 with the Java 1.1 upgrade, try the
Java 1.1 version instead.
Outline instructions
The filter design is based on the following choices of settings:
- Filter type: low pass (LP), band pass (BP) or high pass (HP)
- Analog prototype: Butterworth or Chebyshev
- Filter order: maximum 16; must be even for a BP
filter
- Filter passband: based on sampling rate of 8000 samples/s
(maximum signal frequency 4000 Hz)
- Passband ripple: maximum tolerable variation in filter gain
within the passband, expressed in decibels (Chebyshev filter only)
After choosing values for these settings, click the "Design"
button to design the filter. Once the design calculations have been
completed, click the appropriate button to display either of the
following:
- Poles/Zeros plot
- This shows the locations of the filter poles and zeros in the complex
z-plane, together with the unit circle. By convention, the zeros
are represented by circles and the poles by crosses. Note that the
design method used here results in multiple zeros: an nth
order low-pass filter, for example, has n zeros located at z = -1,
while a high-pass filter has n zeros located at z = +1.
A band-pass filter, which must have even order, has equal numbers of
zeros at both these locations.
- Frequency response plot
- This shows the filter gain as a function of frequency over the range
0 - 4000 Hz (based on a sampling rate of 8000 samples/second). The gain
is plotted in dB, with 0 dB at the top. The minimum plot gain, at the
bottom of the plot scale, can be set by the user to -10, -50, -100 or
-200 dB, to allow different levels of detail to be shown.
Click the Coefficients button to list the filter coefficients.
These are normalised to make the maximum filter gain equal to 1 (0 dB).
If you wish, you can copy and paste the coefficient list to a text editor;
this will enable you to save the coefficients to disc. (A Java applet
isn't allowed to write to your local drive).
Download source
code (zip Archive)
FIR
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