Design FIR and IIR filters interactively. Adjust cutoff frequency, order, and type. View magnitude response and pole-zero plots.
Specify whether the design is FIR or IIR, choose an available filter type, and adjust its cutoff frequency and order. The page lets you judge each candidate through a magnitude-response graph and a pole-zero plot before using the design elsewhere. The easy mistake is to treat cutoff as a brick-wall boundary. A realizable digital filter has a transition region, and changing its order or FIR/IIR structure changes the curve around the selected cutoff.
The magnitude plot reports gain across frequency for the current filter. Use it to identify passbands, rejected bands, and the transition around cutoff. Order is not a direct attenuation control: changing it changes the transfer function and therefore the whole curve. Read the displayed response instead of assuming that every frequency beyond the cutoff is completely removed.
The pole-zero view maps roots of the transfer function in the complex z-plane. Zeros are roots of its numerator, while poles are roots of its denominator. Angular position relates to frequency behavior, and pole radius relates to decay. For a causal IIR filter in reduced form, BIBO stability requires every pole to lie strictly inside the unit circle.
FIR is useful when inherent BIBO stability or an exactly linear-phase design is important, although linear phase requires suitable coefficient symmetry. IIR often achieves a comparable magnitude transition at lower order, but its poles introduce stability concerns and its phase is generally nonlinear. Neither is always better; compare the displayed response with the requirements of the intended application.
No. Pole-zero geometry helps explain notches, resonances, and stability, but positions alone do not state the gain at every frequency without evaluating the complete transfer function, including its gain factor. Use the magnitude graph to judge passband and rejection levels. Use the pole-zero view to understand structure and, for IIR designs, inspect stability.
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