Sat Mar 21 12:46:14 CDT 2009
Bugzilla from firstname.lastname@example.org wrote:
> Jan Rauberg wrote:
>> Lev Givon <lev <at> columbia.edu> writes:
>>> If you want to create a high-pass filter, just specify the cutoff to
>>> firwin and flip the signs of the obtained coefficients, i.e.,
>>> b = -firwin(N,cutoff)
>> Thank you for the fast response. But in the way as you described I get an
>> inverted low pass figure. That's not a high pass and no solution for my
>> problem too. Perhaps there is another solution? J.R.
> A trivial (not ideal) solution is G(z) = 1-H(z)
Simple inversion won't do the trick - you can invert the spectrum as Jan
suggests, or shift the entire spectrum by pi radians.
from scipy import signal
import numpy as np
1) spectrum inversion G(z) = 1-H(z)
How: Subtract original filter from a kronecker delta function.
2) shift entire spectrum by pi radians
How: Elementwise multiply by (-1)**n
The resulting highpass filters will have different characteristics:
g is complementary filter to h (bandwidth is pi-bandwidth(h))
g1 has same bandwidth as h
These techniques won't work for even length filters, but you probably won't
want an even length highpass filter anyway because of the null at pi
- Tom K.
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