Python is a high-level interpreted general programming language. Python has popular numerical and scientific libraries/packages, most notably numpy and scipy. The scipy.signal package is a powerful signal processing software collection. This tag covers the use of numpy, scipy, and other Python ...

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1answer
36 views

Sub pixel shift causes weird results

I am trying to shift an image on a subpixel level, with the method described here: ...
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1answer
34 views

The Nyquist-Theorm behind the fft

I saw a code in Python in the scipy.org (http://docs.scipy.org/doc/scipy-dev/reference/tutorial/fftpack.html) and found this: First question: Is it right that T = 1/800 <==> fs = 800 Hz fulfill ...
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1answer
20 views

Record and playback has echo/feedback

I didn't mess around with the code here, it was straight from their website, I just want to see if it would work. However, whenever I run it, it has feedback in it, sometimes I can't hear anything at ...
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34 views

How would you select the top n frequency of a sample from a noisy audio file?

I am trying to select the top n frequency spectrum from a wav file for my feature vector ...
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1answer
31 views

Why do we need to normalize a WAV file before calculating the FFT?

I am trying to calculate the FFT of a signal stored in a WAV file using SciPy. I found a solution here, but it seems like we need to perform this step before the FFT: ...
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1answer
17 views

One representative time series signal from multiple time series data

I came across this basic problem in DSP which is not my area owf expertise but I consider this problem to be a common problem which others might be addressing. I have multiple time series data and I ...
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0answers
18 views

Feature extraction - DWT

I am new to DSP, I know a quite bit about Python. I have started to code to classify audio (wav files) ...
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0answers
14 views

Template matching results when the template is not on the original image

For testing purposes I'm building a bot that clicks on buttons in the screen. I have a folder with all the possible buttons that needs to be pressed and the application being tested only has one ...
2
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1answer
86 views

Applying filter in scipy.signal: Use lfilter or filtfilt?

I saw in a SO thread a suggestion to use filtfilt which performs backwards/forwards filtering instead of lfilter. What is the ...
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2answers
70 views

Butterworth filter in python

I'm trying to use a Butterworth filter in Python as described in this thread with these functions: ...
0
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1answer
28 views

Smooth X,Y,Z data with discontinuous, artificial jumps

I have some data $(X,Y,Z)$, which is a set of measurements $Z$ over a $2D$ space $X$,$Y$. The $Z$ data on this space is continuous except for some discontinuous jumps in certain domains of $X$,$Y$ ...
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0answers
37 views

Python implementation of multidimensional power spectral density with Welch method

I have done my best to write Welch method implementation for python for multidimensional time series and still in the case of one dimensional time series I am getting inconsistent response compared to ...
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0answers
71 views

Extracting the phase of a jittering sine wave using python

The background: I conducted an experiment where I rotated an object (with three-fold symmetry) many times and recorded the projection of the object. I should be able to tomographically reconstruct ...
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0answers
92 views

In a signal there is a peak, I want to find the start of the peak and the end of the peak

I want to the start time and end time for the peak shown below. The start and end are shown by the marked circles in the fig As there are number of such plots and want to know start and end time for ...
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0answers
69 views

GCC-PHAT cross correlation

I am trying to implement GCC-PHAT in python. The approach is similar to the following two links: link1 and link2 It seems the only difference between GCC-PHAT and normal cross-correlation using FFT ...
0
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1answer
39 views

float image to integer type image

I have a multispectral satellite image and I would like to "transform" each of the image bands into one with integer values. For example to stretch? the image between 0 and 255. Not sure how to ...
1
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1answer
56 views

correct for shift from butterworth filter?

I have implemented a python butterworth filter but it seems to shift the data a lot, the x location of my data is very important to me for my analysis. Is there a way to correct for this shift ...
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2answers
69 views

How to change the start point of resampling process?

I'm trying to resample a digital communication signal in SciPy or Matlab. Suppose the signal was sampled at 3 samples per second, and I want to resample it to 2 samples per second, the thing is I also ...
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0answers
59 views

Using Python with scipy.signal firwin, how do I know how many taps/coefficients should be used?

I need to alter an FIR filter which I know very little about. I have a signal which need to be altered, and looking at a Python script used for this task, I see that it uses Scipy's signal library, ...
0
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1answer
52 views

Advice on filtering a CW signal for processing

This question is related to my other recent questions. In the last question, I learned that I should filter about 4 * WPM (words per minute) around the carrier frequency if I want to recover Morse ...
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1answer
54 views

How to decode Morse code (CW)

I have two related questions on this topic. First, about how wide should the filter be around the carrier frequency? What is used to determine this? Second, in Python, I must use 'numtaps' when ...
0
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1answer
204 views

python; audio; detecting silence in audio signal

I have real-time audio application written in python, and I have question about detecting silence. What's the most efficient way to distinguish silence from non-silence, in an input audio signal? By ...
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2answers
43 views

Color artifacts in Fourier transformed image

I am working with images and Fourier transforms. I am trying to understand what might be causing some artifacts in my output image. I am starting with a 512x512, RGB image of Lenna. I FFT the ...
1
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1answer
80 views

Simulation and theory of first-order low pass filter

I am trying to teach myself some signal processing and control theory. I'm currently working through THIS tutorial. I've started an ipython notebook to keep my notes in. Unfortunately, something is ...
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2answers
73 views

What is wrong with this method of detecting the presence of a signal?

I am trying to decode Morse code from an audio (wav) file. Here is the technique I am using to detect the presence of the signal: I have a window of size (sampling_freq/tone), where tone is the ...
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2answers
47 views

Amplifying part of a signal

If I want to amplify a certain frequency in a digital signal, can I just take the FFT, increase the real part of the value for the frequency I want (leaving the imaginary part alone), and then take ...
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2answers
90 views

Filtering a Morse code (CW, OOK) signal

I am building a morse code decoder in Python. I am using SciPy and Numpy for FFT, filter, etc. It is coming along ok, but the signal is noisy. I am extracting the dominant frequency from the FFT of ...
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0answers
43 views

Gettiing a rectangular waveform from OOK in Python

I have a wave (wav) sound file with on-off keying. I can read the signal value at any point in time (granularity of the sample rate) from an array. I want to create another array, the same size as ...
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2answers
243 views

Image Processing: Flatten a 3D Ball

There are many descriptions of how to turn a 2D image into a 3D one, however I want to do the opposite, in particular to a ball. As an example, consider the following ball: If only the (relatively) ...
1
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1answer
78 views

Filtering method that minimizes ringing in time domain, implementable in Python

I am acquiring data through an oscilloscope, which I am then filtering. I am doing all of this in Python. I need a bandpass filter with stop bands from 0 to .4MHz, and 4MHz and up. My pass band needs ...
3
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1answer
94 views

Confusion about result of FIR All-pass filter design

I try to design a FIR All-pass filter with random phase in the frequency domain. I am a bit confused by my result and am not sure if the reason is a programming error or a misconception about ...
1
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1answer
121 views

Transfer function determination from input and output data

I have some input and output data that I believe adequately includes excitation of the important dynamics of a system. I know it is at most a 4th-order transfer function. How can I identify the ...
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0answers
87 views

Signal leveling using scipy

Apologies if I'm using incorrect terms, and if this question's already been answered here. I have a data set which consists of a high DC signal modulated by AC signal (taken from custom-built ...
5
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2answers
301 views

Image processing coding

I was wondering which is the best language for image processing? I know MATLAB has a good library and user community for it. I havent checked it out, its there for python as well. What is the most ...
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0answers
103 views

How can I specify the scale parameter of the wavelet in PyWavelets (pywt)?

When computing wavelet transforms with PyWavelets (Discrete Wavelet Transform in Python), e.g. ...
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0answers
76 views

PSD Estimation: Welch's method with median averaging

I would like to use median averaging when making a PSD estimate via Welch's method. I notice that this is available as an option in R welchPSD, but not in SciPy or Matlab (in which the default is mean ...
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2answers
159 views

How can an FFT plot not be symmetrical?

From discussions all over the internet, I understand that in a 512 sample point fft, only the first 256 contain relevant information provided that my signal is real. The other half contains complex ...
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2answers
141 views

How to interpret results of Fourier transform by using Python

Connected with this topic , I would like to have some clarifications about the Fourier Transform and the Python tools that make it. Having my data set whose plot is showed in the above link, my array ...
1
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1answer
273 views

How to find the inflection point in a noisy curve?

I have the the noisy curve defined by numpy 2D array: As you can see, it has the first flat segment, then rise, peak and decay phases. I need to find the starting point of the rise phase, marked ...
0
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1answer
1k views

Plot real-time FFT using matplotlib

I'm trying to plot fft in python. I use pyalsaaudio for capturing audio in PCM (S16_LE) format. I use the ion() and draw() functions in matplotlib to have the fft plotted in real time. This is the ...
0
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0answers
13 views

Reference Pattern in Background

I want to apply a nonlinear matched filter to an image to find the reference pattern in the background. The image is just a white box in the foreground with a black background. I've included the code ...
1
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0answers
57 views

Lowpass then Inverse filtering in python

I wrote a simple lowpass filter in python to run against lena. Now I'd like to add Gaussian noise to the lowpass filtered data and then run an inverse filter against the lowpass and try to get the ...
0
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0answers
32 views

Correcting outliers using the standard deviation of a two-point different function?

I recently read a research paper that discussed how to correct lightcurve data (flux vs. time) by using the method as explained below: We have considered as outliers in the datasets the individ- ...
4
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3answers
2k views

Continuous Wavelet Transform with Scipy.signal: what is parameter “widths” in cwt() function? How do time-frequency?

I search to display a time-frequency signal with an original discrete temporal signal (sampling step = 0.001sec). I use Python and the library Scipy.signal. I use the function ...
1
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1answer
85 views

Finding horizontal count of items in an image

I'm trying to find the count of horizontal columns in an ordered image (a sprite image that is used to generate an animated image): From this image, I'm trying to generate a meta-data file like so: ...
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0answers
55 views

How do I combine a copy of a signal with the original to achieve a chorus effect in a .wav file using Python?

Can you please explain or point the right way to think about how to implement two sound effects in a .wav file. So I read a .wav file and converted it to int values (in ...
1
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1answer
822 views

Bandpass butterworth filter frequencies in scipy

I'm designing a bandpass filter in scipy following the cookbook. However, if I decrecrease the filtering frequencies too much I end up with garbage at high order filters. What am I doing wrong? ...
0
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1answer
155 views

Python scipy.fftpack.rfft frequency bin mapping

I'm trying to get the correct FFT bin index based on the given frequency. The audio is being sampled at 44.1k Hz and the FFT size is ...
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0answers
112 views

Shifting of Shift-Invariant Wavelet Transforms

Main Question: Why would iterative wavelet/inverse-wavelet transforms cause a shift along the x-axis for undecimated (shift-invariant) wavelet transforms? I am attempting to remove backgrounds from ...
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1answer
117 views

Inverse of Wavelet Transforms - Background and Noise Removal

Main Problem: How can you inverse Wavelet Transforms (Using the data given by signal.scipy.cwt) I was wondering if anyone understands the ...