An Infinite Impulse Response (IIR) filter produces an output, *y*(*n*),
that is the weighted sum of the current and past inputs, *x*(*n*), and
past outputs.

The Linear Predictive model is a specical case of an IIR filter and shown in figure 7.

The general IIR filter (figure 8) is given by:

**Figure 8:** The general linear filter

If *p* = 0 then the system represents a finite impulse response (FIR)
filter. If *p* is not zero, then the system is an infinite impulse
response (IIR) filter.

An example is the two pole resonator with center frequency and bandwidth related to r is:

Common types of IIR filter:

For more details see [4].

Speech Vision Robotics group/Tony Robinson