Page 212 - Mechanical Engineers' Handbook (Volume 2)

3 Basic Digital Filter 201

Table 2 Comparison of Characteristics for Commonly Used
Windowing Functions
Minimum Stop-Band
Window Name Attenuation (dB)
Rectangular 21
Bartlett 25
Hanning 44
Hamming 53
Blackman 74

(i) 1 i 0

0 i 0 (34)

We construct a bandpass by filtering the data with a high pass-filter, then filtering the output
with a low-pass filter. Or we can combine the two filters together into a single filter by
convolving the coefficients.

3.3 Design of IIR Filters
The common strategy in designing IIR filters is as follows:

Step 1. Design a rational function in the S-domain in factored form that best approximates
the desired frequency response characteristics (using Butterworth, Tchebyshev, elliptical,
etc.).
Step 2. Transform the poles and zeros into the z-domain

Figure 10 Comparison of FIR filter with Hanning window and with windowing.