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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39 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
63 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
41 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
48 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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20 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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193 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) ...
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1answer
50 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 ...
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1answer
61 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 ...
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1answer
49 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
41 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 ...
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2answers
251 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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52 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
39 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
117 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
73 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 ...
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1answer
117 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 ...
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1answer
525 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 ...
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0answers
10 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 ...
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0answers
37 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 ...
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28 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- ...
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2answers
490 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 ...
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1answer
47 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
48 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 ...
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1answer
378 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? ...
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1answer
113 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
79 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
86 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 ...
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1answer
94 views

Interpret numpy.fft.fft2 output

My goal is to obtain a plot with the spatial frequencies of an image - kind of like doing a fourier transformation on it. I don't care about the position on the image of features with the frequency f ...
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2answers
146 views

Iterative Hard Thresholding python implementation [closed]

I'm trying to implement the Iterative Hard Thresholding recovery algorithm for compressive sensing in python. It is a very simple algorithm, given $ \mathbf{y}( = \mathbf{A}\mathbf{x}), \mathbf{A}$, ...
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2answers
135 views

Spectrogram - Am I missing something?

I have the following signal: I'm trying to compute a Spectrogram algorithm, but, don't think I'm doing it right.. I have computed the following: 1) STFT (size 256 with an overlap of 128) 2) ...
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1answer
63 views

How do I compute the DC component given the other part of the Fourier spectrum?

I often see examples in textbooks where someone constructs a 2D Fourier spectrum of an image by fixing two (symmetric) pixels to a given value, and computes the inverse DFT to get a nice waveform ...
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0answers
486 views

numpy.correlate and autocorrelation; audio signal

I want to calculate delay between an input and an output audio signal of my audio processing system. The input and output signals are available as signed 16 bit integers. To try out, I tried the ...
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1answer
174 views

Removing a sinusoidal artifact from a set of movie frames

I am doing some post-hoc analysis of a dataset consisting of a series of movie frames that are contaminated by a strongly periodic artifact. I would like to remove this artifact from my frames. For ...
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1answer
62 views

period detection for a series of photons

I have a dataset which records the arrival time for a series of photons. I am using lomb-scargle method of scipy.signal to try to find some kind of period. Since the arrival time is random,how to ...
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87 views

Subsetting a GeoTIFF Image

I wish to create a subset of a multiband image in OpenCV / Python. The image is in the GeoTiff format. The bands might be 16 bit or 8bit. How do I achieve this using OpenCV and Python.
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2answers
257 views

Zero-padding in STFT

I a recent topic, it has been told that zero-padding in the STFT can improve it, and avoid some circular convolution related things. Here is my Python code for STFT : ...
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1answer
64 views

DWT with more precise scale

With a signal x of length $2^{16}$, the DWT (computed for example with pyWavelet's wavedec) has only 16 or 17 rows (the wavelet ...
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0answers
96 views

FFT by numpy or scipy

The figure I plot via the code below is just a peak around ZERO, no matter how I change the data. My data is just one column which records every timing points of some kind of signal. For example, I ...
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2answers
583 views

STFT and DWT (Wavelets)

STFT can be successfully used on sound data (with a .wav soundfile for example) in order to do some frequency-domain modifications (example : noise removal). With ...
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2answers
263 views

scipy.signal.wiener for audio processing

Does some have an example of what a Wiener filter (that can be used directly with scipy.signal.wiener) can be useful for, in sound processing (it seems that such ...
1
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1answer
154 views

Synthesize Digital Filter with Arbitrary Frequency-Response

fdesign.arbmagnphase is a MATLAB built-in function that will create a filter that best fits the frequency-response that it is given. I'd like to implement a similar function in Python. What ...
3
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1answer
612 views

Differences between Python and MATLAB filtfilt function

I'm trying to port some MATLAB code to Python and am running into some strange behaviour. I am implementing a 5th order Butterworth bandpass filter. The sampling rate is 30 Hz. Running MATLAB R2012b, ...
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0answers
63 views

Inpainting: which algorithm should I choose? [closed]

I have a 3D data set sampled on a regular grid shown in the Figure below. This data can be interpreted as an image where the point altitude is equivalent to the pixel intensity value. In the middle ...
4
votes
1answer
153 views

Haar series approximation of a function?

I'm trying to code the Haar wavelet approximation of a function. I'm a complete newbie. Edit Below is a pseudo-code of my algorithm for $f: [0,10] \to \mathbb R$, $f(x)=x$. I picked it here and ...
2
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1answer
121 views

Wavelet time extraction

I am trying to understand one simple thing in wavelets and I searched a lot, but did not get any idea. I need to perform Multilevel 1-D wavelet decomposition on my signal. I have arrays ...
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4answers
1k views

generating spectrograms in python with less noise

I'm trying to do something similar to Shazam (paper here) in Python. Basically the idea is to use FFT with sliding window to transform both WAV files and recorded audio to the same spectral ...
0
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1answer
112 views

Compute PSD from a CSV file

I'm sorry if my question might be simple, but I don't have a strong background on signal processing. I have a csv file of a 8 MHz bandwidth, sampled with a resolution bandwidth of 100 KHz. What I want ...
3
votes
1answer
96 views

Constraint on a filter

First of all thanks for your patience: it is the first time for me posting a question in this forum. I am not a DSP expert, but I should get by if you give me in depth explanation. This is an example ...
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2answers
741 views

Algorithm to zero pad data before FFT

I've seen some other questions on here about zero padding (like this one) but I'm still a little confused about my situation. I'm attempting to zero pad my input time series data, so I get an ...
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2answers
198 views

how can I calculate pitch deviation in a large collection of audio files?

I am making a software model of an existing digital synthesiser and I have made audio recordings of single notes with particular parameter settings. I made a program in C++ which sends a MIDI sysex ...