Skip to main content

Frequency domain filtering in python

Original signal (buried in 3 kHz noise):

Discrete Fourier Transform:

Get rid of offending noise spikes in frequency domain:


Cleaned signal (black) compared to original noisy signal.


And all this takes a few lines in python+scipy+matplotlib using scipy's signal processing module:


import scipy.signal as ss
import pylab

censor0 = pylab.array([[860,875], [2590,2615],[4330,4350],[5885,5893],[6885,6893]])
censor1 = len(x_orig) - censor0[:,[1,0]]
censor = pylab.concatenate((censor0,censor1))

x_orig = data['currents'][1][1][1][0] #The data
X_orig = ss.fft(x_orig)
X_filt = pylab.array(X_orig)
for n in range(censor.shape[0]):
X_filt[censor[n,0]:censor[n,1]] = 0
x_filt = pylab.ifft(X_filt)

Comments

Popular posts from this blog

Python: Multiprocessing: passing multiple arguments to a function

Write a wrapper function to unpack the arguments before calling the real function. Lambda won't work, for some strange un-Pythonic reason.


import multiprocessing as mp def myfun(a,b): print a + b def mf_wrap(args): return myfun(*args) p = mp.Pool(4) fl = [(a,b) for a in range(3) for b in range(2)] #mf_wrap = lambda args: myfun(*args) -> this sucker, though more pythonic and compact, won't work p.map(mf_wrap, fl)

Flowing text in inkscape (Poster making)

You can flow text into arbitrary shapes in inkscape. (From a hint here).

You simply create a text box, type your text into it, create a frame with some drawing tool, select both the text box and the frame (click and shift) and then go to text->flow into frame.

UPDATE:

The omnipresent anonymous asked:
Trying to enter sentence so that text forms the number three...any ideas?
The solution:
Type '3' using the text toolConvert to path using object->pathSize as necessaryRemove fillUngroupType in actual text in new text boxSelect the text and the '3' pathFlow the text

Drawing circles using matplotlib

Use the pylab.Circle command

import pylab #Imports matplotlib and a host of other useful modules cir1 = pylab.Circle((0,0), radius=0.75, fc='y') #Creates a patch that looks like a circle (fc= face color) cir2 = pylab.Circle((.5,.5), radius=0.25, alpha =.2, fc='b') #Repeat (alpha=.2 means make it very translucent) ax = pylab.axes(aspect=1) #Creates empty axes (aspect=1 means scale things so that circles look like circles) ax.add_patch(cir1) #Grab the current axes, add the patch to it ax.add_patch(cir2) #Repeat pylab.show()