| DSP Blockset | |
Lowpass and Highpass Discrete-Time FIR Filters. The magnitude response illustrated below shows a lowpass order-41 FIR filter with normalized cutoff frequency fn0 = 0.5. The right plot shows a zoomed view of the transition region. For an input signal sampled at 1 kHz, this filter would provide a cutoff frequency of 250 Hz.
The equivalent MATLAB code for this filter design is
b = fir1(41,0.5)
and the filter can be designed in the Digital FIR Filter Design block by making the following selections in the dialog box:
410.5The cutoff frequency for a highpass filter (Highpass selected from the Filter type menu) is defined in the same way: -6 dB down from the passband level. The equivalent MATLAB code for the highpass filter design is
b = fir1(41,0.5,'high')
For highpass designs, the filter order must be even (so that the filter is Type I). MATLAB therefore automatically increases the filter order to 42 for this example.
| | Specifying Classical Discrete-Time Filter Parameters | Bandpass and Bandstop Discrete-Time FIR Filters | |