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# Questions tagged [numpy]

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### Aligning/syncing one audio file to another using Python

I have 2 audio files recorded using laptop mic and one with external mic. Laptop mic recording starts after external mic. The time difference could be 2-60 seconds. So I wrote this code which is ...
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1 vote
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### FFT2 to RFFT2 Fourier plane and similarities

I'm trying to understand how Python's fft2 is different from irfft2. Basically, I have some continuous Fourier 2D samples that I need to put in a (n,n) grid (this can be done by a simply count-in-cell ...
55 views

### Vectorizing calculation of slew rate envelope

I am working in a problem where for many stored signals (hundreds of thousands), I need to compute the slew-limited version of each signal. The slew-limited version will start with the same initial ...
44 views

### Is it possible to use np.fft.fft to pick out the Fourier coefficients from one timepoint, at a specific frequency?

I am trying to apply np.fft.fft on a 2D array of data of shape (98, 1024), where 98 is the number of trials and 1024 is the sampling rate in Hz. I am trying to find ...
122 views

### what does librosa.stft do that makes it different?

My understanding of the Short Time Fourier Transform is that first I need to frame the signal and window it, after that apply an fft on these windowed frames. Using Librosa: ...
1 vote
103 views

I am trying to implement an SDR transmitter and receiver based on the description here. ...
139 views

### Why does my irFFT function have a small discrepancy distributed through the entire output?

Since I've last posted on dsp@stackexchange, I have been working on my algorithms and recently came across a useful radix-2 implementation which delivers performance as good or better than that of ...
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504 views

### python how to demodulate iq fm signal that was moved to 0 frequency

I am struggling with implementing FM demodulation for IQ samples that has 0 center frequency from RTL-SDR ... I have found the following algorithm for FM demodulation, see FM demodulation: ...
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1 vote
325 views

### Overlap and Add/Save Inverse Short-Time Fourier transform

Edited for conciseness, please see below: Question: How does overlap and save work, in the context of array buffers? How does overlap and add work? For a specific use case involving STFT, which one is ...
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305 views

### polynomial is not fitting well

I have two signal spectrums. I represent them with polynomial coefficients and then do convolution. fig 1 & 2 are the two signal spectrums and their corresponding polynomial representations. (I ...
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339 views

### Vectorizing a biquad filter (python / numpy)

I'm having a lot of fun writing signal processing code in Python / numpy, and I'm resisting the urge to pre-optimize the code. But my biquad implementation is slower than I want. Here's the inner ...
1 vote
198 views

### Weird Noise arises on the small scales: one question about the fast CWT algorithm implemented in real space

Background: I am learning an interesting Fast CWT algorithm(PPCWT) by reading this paper published in 2019. The algorithm is summarized as below. The continuous wavelet transform of a signal can be ...
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1 vote
123 views

### Does the resolution of a timeseries affect the estimate of the power-spectrum when using np.fft.rfft and does it comply with parseval's theorem?

I have been trying to estimate the power spectrum of a timeseries using fourier transform. I have tried to do this using two variations of the spectral density estimate using np.fft.rfft. The two ...
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### SDR - Manual FFT PSD vs pylab PSD

I am trying to calculate the power spectral density step by step using numpy FFT and comparing it to the PSD calculated by pylab PSD. Difference b/w plots of both methods can be visualized from in ...
97 views

### Decimate a signal whose values are calculated, not stored

tl;dr I'm looking for something like Scipy's decimate function, but one that takes in a generator, rather than a Numpy array. I am turning on and off a light using ...
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56 views

### How to achieve uniform gaussian profile? Beam profile has grainy/multimode pattern

Hi apologies in advance if this (optics & image-process) is not where I should post this question. Thanks for the help! I'm required to make a jig that measures the divergence angle of a ...
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5k views

### When concatenating sine waves, how do I phase shift in order to prevent "pops" caused by sudden jumps in amplitude?

I'm writing a synthesizer using numpy and python. I've run into a problem where concatenating sine waves causes 'pops' or 'clicks' when they are outputted to audio, say, via ...
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437 views

### Simulation of Lock-In Amplification in Python makes no sense

I would like to simulate a basic lock-in amplification for post-processing some data. I wrote a basic Python script for this purpose but the output of the lock-in amplification does not seem to make ...
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### How can to obtain the transfer function of a bandpass digital filter? [duplicate]

I've been asked to: create a bandpass filter amplifier in python, determine the transfer function, graph the bode diagram, and print the highcut frequency, lowcut frequency, the bode constant and the ...
1 vote
368 views

### Resample signal and start from a different point with numpy.interp

I am trying to resample a signal in Python, only by giving the new and the old step. My function works fine until here. But now I want to start the resampled signal at a specific point other than the ...
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737 views

### More Efficient Frequency Shift + FIR Decimation

I am dealing with complex IQ data from a software defined radio. I'd like to digitally shift the spectrum by some amount to center an off-center signal, then decimate down to that signal only. ...
1 vote
533 views

### How to center the FFT of sine wave in matplotlib?

I want to plot the FFT of a sine wave using matplotlib and I want to plot a single line at a frequency where the sine wave belongs. here's my code ...
686 views

### How to train a FCNN with Spectrogram images?

I'm working on a audio dereverberation deep learning model, based on the U-net architecture. The idea of my project came from image denoising with auto-encoders. I feed the reverberated spectrogram to ...
1 vote
421 views

### Scipy FFT and Numpy FFT disagree on pulse train spectrum?

I am doing an FFT on a series of pulses. The series is one pulse of amplitude 1 every 7 days over a total of 367 days. The code below is what I run: ...
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### Numpy 2D FFT produces corona that is not uniform around center

Tldr: Numpy FFT creates non uniform output when output is wanted to be uniform. I want the output to be a uniform corona. I am trying to eventually run a Gerchberg-Saxton phase retrieval algorithm. I ...
38 views

### What is the difference between sampling over $-4\pi$ to $4\pi$ and 0 to $8\pi$

I see no difference in magnitude, but the phase plots vary significantly while using NumPy and MatPlotLib to plot. Looking at the phase plots, I feel like I'm missing something important. Also, I'm a ...
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179 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 ...
1 vote
279 views

### Why does numpy FFT only work for samples of 10,20,30 sec?

I'm using numpy FFT functions to find the amplitude, frequency and phase of low frequency signals. focusing between 0-10 hz.Part of my project is to vary the time over which the sample is taken and ...
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89 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 ...
3k views

### Scipy butter filter - remove DC offset w/ high sample rate

I am having a hard time figuring out how to employ a high pass filter to remove the DC offset of my data signal with the "scipy butter" function because my sample rate is quite high. The ...
293 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....
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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: ...
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314 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 ...
723 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 ...
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172 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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1 vote
523 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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### 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, ...
1k 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 ...
275 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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261 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\...
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### 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 vote
200 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 ...
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1k 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 ...
321 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 ...
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