[PD] how to create a lowpass filter from first principles?
geoffspuredata at googlemail.com
Thu Jan 22 20:45:59 CET 2009
I am new to Pure Data,
I downloaded and have played around with it for the last couple of
days and it is rather wonderful.
I can quite happily create a basic synth inside it without too much
The reason I wanted to use Pure Data was to implement some of the
maths that I am learning through a couple of DSP books that I am
The DSP book I have read gives a simple lowpass filter function as
g(n) = (f(n-1) + f(n) + f(n+1))/3
i.e the average value of three consecutive samples. I understand how
this is in effect a lowpass filter.
How do I implement that in PD?
I can easily connect a Oscillator (phasor) object to a lowpass filter
object to the DAC and hear it working,
However I want to be able to create my own lowpass filter i.e. try to
really understand how things are put together.
Therefore if in the function above I need 3 consecutive samples, I
would have thought that I need some kind of buffer to hold and call
those samples from,
so that I can then call three samples average them and then output
that, however that would have to move at the same rate/freq as the
audio engine is set up i.e. 44100Hz ..... errrr.
So I am thinking about how to solve the problem I just seem to be
missing how to start.
Any guidance appreciated.
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