Digital filter design with Matlab

Closer approximations to the ideal digital filters than our simple examples can be had at the expense of more complexity (i.e. more zeros and or poles in H(z)). The diagram below illustrates a better low pass filter than our previous example.

The deviations from ideal properties include :

• Ripple in the pass band
• A finite transition width
• Non-zero response outside the pass band
• And non-linearity of the phase response
• If the design is of high order (many delays in the equivalent DE) the total delay through the filter may be a nuisance

Various filter designs have been invented and the most useful ones are implemented in Matlab. In the various designs there are trade-offs between non-ideal characteristics.

• Infinite impulse response (IIR) filters
• Finite impulse response (FIR) filters