Questions tagged [numpy]

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2answers
170 views

Using fft to calculate vsdft

We are currently implementing the velocity synchronous discrete Fourier transform (vsdft) for order tracking rotating machinery in Python. The formula is similar to dft. Simplified, it is given by $...
6
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2answers
514 views

Quantization SNR of sine wave doesn't match 1.761 + 6.02 * Q

I am trying to show with numpy that the quantization noise of a sine wave matches the SNR formula of SNR = 1.761 + 6.02 * Q. The numpy code is simple: ...
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1answer
95 views

Analyze PCM data

I am getting some 16 bit PCM data (raw bits) from a serial port . I need to collect this stream of bits using some python application running in PC and store it somewhere(Assume it in an array). I ...
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2answers
215 views

Shifting signal smaller than discrete step

I have a image that I need to shift with less than a pixel. My plan was to do a Fourier transform and multiply the signal with $e^{-aiu-biv}$ where $a, b$ are the shifts in x and y direction. This ...
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2answers
9k views

Avoiding “RuntimeWarning: invalid value encountered in log10” when converting FFT data to dBFS

I've attached some code below that I'm having some issues with. Basically, I need to write a function to get the dBFS value of a signal at a specified Hz value, at a given channel in a .wav file. ...
0
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1answer
34 views

Equal probability quantizer in Python

I am trying to apply Haralick textures to a SAR image (float32). As far as I know, the image first needs to be quantized to a reasonable bit depth prior to calculate the co-ocurrence matrix. In the ...
0
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1answer
28 views

FFT of shifted image in Numpy

I want to prove using numpy the theory of Fourier transforms in which translation in space corresponds to a shift in the phase domain (frequency domain remains constant). I have generated these three ...
0
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1answer
147 views

Choppy output when trying play through a callback buffer

I am trying to make a keyboard in python where every note's frequency is a ratio of the previous note but my output is strangely choppy for some reason. Here's an example of what I mean. I'm using ...
2
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1answer
85 views

How to get an interpolation weight from a mathematical definition

It was recently explained to me that a "Nearest neighbor" kernel for 1D interpolation can be implemented like this using NumPy ...
0
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1answer
41 views

Output shape of numpy's rfft function

For numpy's rfft function, the length of the output is about half of N, the length of the input sequence. What is the reason behind this? What are the frequency bins?
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0answers
40 views

How to save MFCC features and frame energy of several wav files to one .npz file for machine learning training?

I am creating a English-Italian corpus of around 100 hours of English audio from LibriVox aligned with their Italian textual translation. The alignment is at a sentence level and the corpus consist of ...
0
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0answers
31 views

Why is there a difference in the spectrum of an audio file between Sonic Visualizer and my Python script?

I am working on a script which is creating a spectrum analysis from an audio file using SciPy and NumPy. Before I started, I analyzed the file using Sonic Visualizer, which got me the following result:...
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1answer
46 views

Autocorrelation - Understanding reduced correlation at periodic time shifts using np.correlate (versus statistical autocorrelation)?

I'm going through the Think DSP by Allen B. Downey, and I'm struggling to understand a specific aspect of np.correlate and how it differs from statistic autocorrelation. The question is at the bottom, ...
1
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1answer
73 views

Gaussian signal generation

Edit: Could the following be the answer? Generate WGN-like-signal which is centered around a set dBm value. Treat that signal like it was a frequency domain representation of an unknown X time-domain ...
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0answers
54 views

Understanding outputs of image Fourier Transform in Numpy

I am trying to understand the meaning of FFT outputs with respect to images. Take a look at the following example: ...
2
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0answers
57 views

fft formula convention

I try to code up an algorithm from a scientific paper where they solve a differential equation using Fourier transforms. In the paper, they use the FT convention $\rho(x_i) = \sum_{k=-m}^m r_k e^{i2\...
6
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1answer
329 views

Morphing between two FFTs

I'm a musician and I'm making a script that takes a wave file and snaps each of its frequencies from the fourier transforms to the nearest musical harmonic. Thanks to help from another question I ...
0
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1answer
37 views

How to produce color image using edge detected images?

Hi I am trying to produce an image which is a combination of multiple images such as in focus stacking. Now I have 6 photos and I want to produce a final image such that the final image uses blocks of ...
1
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0answers
60 views

Why are low frequency peaks not sharp in scipy fft?

I am using numpy/scipy to plot graphs of sine waves. frequencies at 15 Hz or higher give nice, sharp peaks, but at lower frequencies, the peaks are smeared and the actual peak frequency can't be seen ...
0
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1answer
381 views

Signal processing using numpy python

To process a .wav audio file with numpy (using fast Fourier transform algorithm). I want to process an audio signal at a particular interval with a sampling frequency 44100hz and sampling rate of 20ms ...
0
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1answer
2k views

Autocorrelation: numpy versus FFT

I have a series a of values (0 and 1) coming from a Brownian process with drift for which I am studying the autocorrelation. I used two methods: 1) numpy autocorrelation: ...
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0answers
30 views

delayed result in sinc upsampled signal

I have implemented an infinite kernel sinc interpolation. For some signals I notice an artifact, visible at the right end of the plot. I am wondering: is it a bug in my code or a phenomenon usual for ...
3
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2answers
2k views

Understanding a simple case of fft2 in python

I have 2D arrays representing surfaces. I have created them by scanning some theoretically flat objects and I ended up with what can be called "imperfections", or else, deviation from the perfectly ...
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0answers
187 views

Is there any python code for applying a-law/mu-law on 3D numpy array?

I have 3D numpy array of probabilities between [0,1], I need to emphasize on some area with lower probabilities. I was suggested to apply a-law and mu-law. I am wondering if there is python library/...
5
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3answers
6k views

Looking for Fastest 2D Convolution in Python on a CPU

Convolutions are essential components of many algorithms in neural networks, image processing, computer vision ... but these are also a bottleneck in terms of computations... In the ...
0
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0answers
6k views

AM Modulator Demodulator in Python

I am trying to make a AM modem using Python Numpy and Matplotlib. I am successful in generating the AM Signal but I cannot demodulate it using a lowpass filter function that I made. The demodulation ...
0
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1answer
381 views

Extrapolate a 2D array using Fourier Transform

I need to extrapolate a given 2D array to a larger domain, keeping the spatial frequency. This is the original field: (the data file in numpy npz format and a Jupyter notebook to plot it can be found ...
1
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1answer
132 views

OFDM Simulation process

I'm trying to understand OFDM by making a simulation. Are these steps correct? generate M random complex QAM symbols. example: (1+j,1-j,-1-j,1-j....) Split my M samples into a N 2048 sized arrays ...
1
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1answer
6k views

Image processing based on wavelet transform in python [closed]

I take the dwt2 for an image and saved it's coefficients (LL,Lh, hl,hh) using pywt.dwt2 (image,'haar'),in my project I have to change them to uint8 but when I change their types and reconstruct the ...
1
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1answer
351 views

Fast Fourier Transform using numpy

I am a computer science student and didn't really have signal processing as a subject. Maybe I should be clear on the concepts of sampling rate and frequency of the signal but I am a little confused. ...
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0answers
1k views

Acceleration time series to velocity conversion using DFTs

I have 1000 Hz time series data for acceleration (512 data points), which I want to convert to velocity. I am trying to use the omega arithmetic method to achieve this. Following are the steps I am ...
1
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1answer
2k views

Discrete Fourier transform of an exponential decay

I have a vector with an exponential decay, using Numpy: t=np.arange(128) k=0.1 decay=np.exp(-k*t) I would like to compute the discrete Fourier transform (DFT) of ...
2
votes
1answer
2k views

Amplitude of frequency bin in FFT doesn't match time-domain amplitude

I have a sinusoidal current that I am sampling at about 357k SPS. The current signal is about 3A pk-pk @ 750hz (top figure). I am wondering why when I take the fft using numpy/scipy's fft function, ...
2
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1answer
2k views

Numpy fft2 frequency shift

I don't understand how to make frequency shift in fft2 or higher dimensions. Could anyone explain it, please? import numpy as np import matplotlib.pyplot as plt from mpl_toolkits.mplot3d import ...
0
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1answer
322 views

How to interpret the signal in frequency domain

I'm having difficulties understanding some basics regarding FFT. I was hoping you could answer a few questions I have. These questions will probably seem silly to you, sorry for that. I'm a complete ...
0
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1answer
69 views

Unexpected peaks in power density following downsampling and filtering

I first applied a 100 Hz lowpass filter to my data, which was recorded at 30000 Hz: ...
4
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1answer
1k views

How to generate random samples of Gaussian distribution directly in the frequency domain?

One can easily draw (pseudo-)random samples from a normal (Gaussian) distribution by using, say, NumPy: ...
0
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2answers
3k views

Why is the size of the output of the FFT of a signal is same as the size of the input signal?

I am kind of new to the DSP domain. I was trying to get the frequencies associated with a signal by performing FFT over it. I used numpy.fft.fft for this. ...
1
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1answer
2k views

Result of inverse FFT is sometimes shifted in real space

I am using the Numpy fft2, ifft2, and related functions and I am sometimes running into a strange situation where the output ...
1
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1answer
1k views

Hamming Window, python 2.7 [closed]

Hi I have a FFT which is quite noisy. How to apply to my code Hamming window to make it less noisy. Look at my code: ...