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

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()

Running a task in a separate thread in a Tkinter app.

Use Queues to communicate between main thread and sub-threadUse wm_protocol/protocol to handle quit eventUse Event to pass a message to sub-threadimport Tkinter as tki, threading, Queue, time def thread(q, stop_event): """q is a Queue object, stop_event is an Event. stop_event from http://stackoverflow.com/questions/6524459/stopping-a-thread-python """ while(not stop_event.is_set()): if q.empty(): q.put(time.strftime('%H:%M:%S')) class App(object): def __init__(self): self.root = tki.Tk() self.win = tki.Text(self.root, undo=True, width=10, height=1) self.win.pack(side='left') self.queue = Queue.Queue(maxsize=1) self.poll_thread_stop_event = threading.Event() self.poll_thread = threading.Thread(target=thread, name='Thread', args=(self.queue,self.poll_thread_stop_event)) self.poll_thread.start() self.poll_interval = 250 self.poll() self.root.wm_protocol("WM_DELETE…