Class

Choose the class of filter to create.  There are five from which to choose:

Bessel:

Has the slowest rolloff and requires the highest order to meet an attenuation specification.

Butterworth:

Maximally flat in the passband and stopband, but has a transition region that is less steep than the other filters.

Chebyshev:

Achieves a steeper transition region by allowing ripple in the passband. The stopband is maximally flat.

Elliptic:

Minimizes the transition width by allowing ripple in the both the passband and the stopband. This class generally meets filter requirements with the lowest order.

Inverse Chebyshev:

Achieves a steeper transition region by allowing ripple in the stopband. The passband is maximally flat.