# Questions tagged [numpy]

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### 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: ...
7k 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 ...
415 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 ...
2k 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: ...
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 ...
3k 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, ...
116 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 ...
3k 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 ...
60 views

151 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 ...
88 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, ...
625 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 ...
545 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 ...
3k 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: ...
357 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 ...
87 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: ...
8k 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 ...
22 views

### Problem in constructing complicated block matrix [migrated]

So, Here I want to solve this above equation and determine $(W|a_1 a_2 a_3)$ in Python. However, most of the part I can possible do but I am totally clueless how could I construct such a Block Matrix (...
57 views

### FFT on continuous fifo data - Is y axis magnitude sum of all samples?

I'm running an fft once a second on a buffer of data 60 seconds long. The data is sampled at 558Hz and is placed into the fifo buffer once per second. FFT is numpy.rfft. The data is scaled to psia ...
42 views

### Visualise/compare numpy arrays from Matlab/Octave to matplotlib

I'm new to python and matplotlib, and I'd like to visualise / compare 3 mfcc files stored as numpy arrays in txt format. I have the Octave code below, and I'd like to know how it can be done using ...
42 views

### Establish instantaneous amplitude of signal

I'm using the YIN algorithm to establish the pitch of my humming / whistling voice. This is a time domain algorithm and gives me the instantaneous frequency as a function of time ($f(t)$). I now wish ...
76 views

### Wrong values calculating FFT with EEG Bands using Numpy

First of all I have to say I am very new to these matters. I am trying to apply FFT algorithm to some values obtained by EEG bands. I found the following code but I am unable to make it work correctly....
110 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 ...
266 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 ...
50 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:...
283 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 ...
57 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?
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 ...