Signal Processing Toolbox

Redesigning a Filter Using the Magnitude Plot

After designing a filter in the Filter Designer, you can redesign it by dragging the specification lines on the magnitude plot. Use the specification lines to change passband ripple, stopband attenuation, and edge frequencies.

In the following example, create a Chebyshev filter and modify it by dragging the specification lines:

1. Select Chebyshev Type I IIR from the Algorithm menu.
2. Select highpass from the Type menu.
3. Type 2000 in the Sampling Frequency field.
4. Set the following parameters:
• Fp = 800
• Fs = 700
• Rp = 2.5
• Rs = 35
5. Select Minimum Order so the Filter Designer can calculate the lowest filter order that produces the desired characteristics.
6. Press Apply to compute the filter and update the response plot.
7. Position the cursor over the horizontal filter specification line for the stopband. This is the first (leftmost) horizontal specification line you see.

1. The cursor changes to the up/down drag indicator.

8. Drag the line until the Rs (stopband attenuation) field reads 100.

Note    The Order value in the Measurements region changes because a higher filter order is needed to meet the new specifications.

Designing a Filter with the Pole/Zero Editor

Setting Preferences

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