This post discusses the stability of IIR filters. This should be the last article in this series on frequency filters, unless I find something else interesting enough to write about. The purpose of this series was to show that digital signal processing is not that difficult of a topic. We started with some really simple finite impulse response low pass filters, discussed better filters, tried all pass, high pass, band pass, and band stop filters, checked out various windows, and recently moved to infinite impulse response filters. We have already populated our music wiki with various such DSP related topics, including some relatively complex infinite impulse response filters, such as the Bessel filter, the Chebychev type I filter, and the Chebychev type II filter.