## Filter Design

design_FIR_filter | Create an artibtrary filter or order `order` that attempts to give the frequecny response given by `freq_response`.
design_lowpass_FIR_filter | Design a FIR lowpass filter of order `order` and cut-off freqeuncy `freq`.
design_highpass_FIR_filter | Design a FIR highpass filter of order `order` and cut-off freqeuncy `freq`.

> FIR Filtering is a 2 stage process, first involving design and then the filtering itself. As the design is somewhat costly, it is usually desirable to design a filter outside the main loop.

> For one off filtering operations, functions are provided which design and filter the waveform in a single go.

> It is impossible to design an ideal filter, i.e. one which exactly obeys the desired frequency response. The "quality" of a filter is given by the order parameter, with high values indicating good approximations to desired responses. High orders are slower. The default is 199 which gives a pretty good filter, but a value as low as 19 is still usable if speech is important.

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This page is part of the Edinburgh Speech Tools Library documentation
Copyright University of Edinburgh 1997
Contact: speech_tools@cstr.ed.ac.uk