[PD] how to create a lowpass filter from first principles?

Charles Henry czhenry at gmail.com
Fri Jan 23 00:11:36 CET 2009

On Thu, Jan 22, 2009 at 1:45 PM, Geoff <geoffspuredata at googlemail.com> wrote:
> The DSP book I have read gives a simple lowpass filter function as
> g(n) = (f(n-1) + f(n) + f(n+1))/3

Have a look at fexpr~.  You can write FIR and IIR filters using
fexpr~.  It should be a good learning tool.

Difference equations like these are nearly trivial--I say nearly
becuase you have to note the part that is non-causal above, f(n+1).
Make this into a causal filter with 1 additional sample latency.
e.g.  g(n) = (f(n-2) + f(n-1) + f(n))/3


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