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Questions tagged [stft]

Short-Time Fourier Transform

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22 views

Definition of an adaptive threshold for signal detection

Good day. I would like to try to create a signal detection algorithm based on STFT. I am interested in the implementation of an adaptive detection threshold that will be determined per bin (by ...
0 votes
1 answer
949 views

Cochleagram vs STFT for CNN-based speech segregation

I’m working on a project (python-based) that would use ideal ratio masks (IRMs) as a basis for cleaning noisy speech in various environments. Specifically, this will be accomplished through the use of ...
0 votes
1 answer
114 views

Unwindowed STFT of sine, closed form solution and insights (sliding FFT)

I seek to calculate, mathematically, the unwindowed Short-Time Fourier Transform of $$ \cos(2\pi f t + \phi) $$ i.e. any arbitrary real-valued sine: any frequency, duration, phase shift, and number of ...
5 votes
1 answer
124 views

Interpolation of STFT between time and frequency bins

I am trying to identify and remove airplanes in a time series obtained at a radio meteor receiver. Here we have a spectrogram which displays the power content of my signal as a function of frequency ...
2 votes
1 answer
254 views

Why does NMF (Non Negative Matrix Factorization) decompose a spectrogram into time and frequency component?

I compute the NMF over a spectrogram (magnitude of STFT of a signal) in this way: W,H = NMF(MyStft,r) # where r=2 is the rank W and H respectively contain the ...
0 votes
0 answers
68 views

writing from STFT to audio using ISTFT adding harmonics to audio not present before

I'm doing quite a bit of the samething as I wrote in this post here : Shifting frequency peaks such that w[i] moves to w[i/n] using STFT and IFFT I'll quote from it here to present the issue I now ...
0 votes
0 answers
43 views

Shifting frequency peaks such that w[i] moves to w[i/n] using STFT and IFFT

I am trying to do a kind of frequency compression on say 20 most energetic frequencies in a particular slice of a STFT. If w[i] is the frequency peak for a slice of STFT at a particular time, then I ...
3 votes
2 answers
2k views

Hop size in STFT

I am reading the documentation of scipy.signal.stft function. My question: is the 'noverlap' parameter of this function equivalent with STFT hop size?
0 votes
0 answers
12 views

Calculating PSNR using STFT of sampled signal

I have a baseband IQ sampled signal from a Pluto SDR with a bandwidth B and also fs = B, how can I calculate its PSNR using the STFT of the signal in Matlab. Do I need to take into account the RBW of ...
1 vote
1 answer
74 views

Window Type Effect on Pwelch vs ShortTimeFFT PSD Result?

I am trying to make sure I understand the output scaling of pwelch. I am using the PWelch function to compute the PSD of a signal and I have manually computed the PSD from an STFT output. The results ...
1 vote
0 answers
415 views

How to plot the STFT of a .wav file in GNU Octave?

I'm quite new to signal processing and am trying to find the short time fourier transform of an audio sample and plot it (I believe the best way is as a spectogram?) using Octave (similar to this ...
2 votes
1 answer
142 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
0 answers
86 views

Advantage and Disadvantage using Mel Spectrograms over STFT in speech/waveform synthesis

I want to ask you a question about the waveform synthesis or more spesifically speech synthesis. Most of the state-of-the art papers use mel-spectrograms as their inputs, because it mimics the human ...
1 vote
0 answers
86 views

STFT normalization

In Scipy's implementation of STFT, an argument allows to scale the result as a spectrum or as a psd : ...
5 votes
3 answers
1k views

Is "Windowed Fourier Transform" a synonym for "STFT"?

Sometimes I find the notation WFT (Windowed Fourier Transform) while other times I see STFT (Short Time Fourier Transform). Are they the same?
3 votes
2 answers
137 views

Why not overlap save for inverse stft

Since STFT uses overlapped sections of the input signals and compute DFT, it resembles overlap-save method used for block convolution, instead the overlap-add method for block convolution uses non-...
2 votes
1 answer
79 views

Comparing results for spectrum generating in matlab using STFT and Filterbank approach

To analyse data in the frequency domain I often use functions like stft() in Matlab. Inspired by this video and this article I have compared the results of ...
4 votes
2 answers
947 views

How to calculate short-time fourier transform (STFT) when the window length is greater or smaller than the FFT size?

I have been trying to understand the weighted overlap-add (WOLA) method. By searching papers and posts in dsp.SE, I found that the window length can be larger and smaller than the FFT size. 1. Window ...
1 vote
1 answer
137 views

reproduce Scipy's stft

I failed to reproduce Scipy's stft. When I have tried to remove all the possible modifications and go the minimal example, I converge to the following: ...
1 vote
0 answers
249 views

How to implement STFT for processing audio [closed]

I should start this off by saying I’m a hobbyist and by no means a student. I’ve been reading “The Audio Programming Book”, and attempting to implement STFT on the stm32 based Daisy platform. In order ...
2 votes
1 answer
350 views

What is the difference between STFT and Gabor filter?

My understanding is that a Gabor filter gives us information about when in the input signal does the frequency of interest (equal to the frequency of the sinusoid in the Gabor Filter) occur, thus ...
1 vote
2 answers
321 views

Overall spectrum computation from Short-Time-Fourier-Transform

I am trying to computing the overall spectrum of a given signal from its Short-Time-Fourier-Transform. I am using python to do this and I wrote my function to compute the STFT: ...
5 votes
4 answers
802 views

Why are there beats in spectrogram / Windowed Fourier Transform of sines?

I am trying to understand how the Windowed Fourier transform works, so I used Matlab to create an artificial signal, and plotted the Windowed Fourier transform using a gaussian window. $x(t) = \left\...
1 vote
1 answer
353 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 ...
4 votes
2 answers
1k views

How does the effect of windowing change with the phase of the input signal?

I am calculating the SNR (signal power to noise power) for a sine wave. I don't have an integer number of periods in the waveform being analyzed, so I am using a flattop window to reduce spectral ...
3 votes
0 answers
64 views

Artifact during this STFT spectrogram plotting

I am new to the field of DSP and I am currently working on implementing a real-time audio spectrogram using STFT technique. While making progress, I have encountered an issue when testing a constant ...
0 votes
1 answer
104 views

STFT Audio processing with zeros

In this paper they preprocess an audio file with a STFT and then apply two equations to the computed matrix. I tried implementing all of it in python and used librosa for the STFT. The issue I ...
3 votes
3 answers
3k views

Difference between librosa.stft and scipy.signal.stft

I read the source code of librosa.stft and sicpy.signal.stft, and notice that the calculation results of STFT in these two libraries are quite different: In scipy.signal.stft, the stft result is ...
1 vote
2 answers
170 views

STFT needs circular shift or not?

In some textbooks and websites, circular shift operation is done before doing FFT of windowed data, in the explaination, circular shift is to ensure zero-phase. But in other textbooks and websites(I ...
0 votes
1 answer
287 views

Construction of Room Impulse Response - Short-Time-Fourier-Transform and Inverse-STFT - Matlab and NWaves (C#) Implementation

Background: I am working on a Unity Project (C#) and implementing a Room Impulse Response synthesis. I do ray tracing to create energy histogram for different bands. With these histograms it is ...
1 vote
3 answers
381 views

Increasing STFT resolution by repeating the window? Ways to improve STFT resolution?

In theory of FT(Fourier transform) and STFT(Short Time Fourier Transform) it is said that "A narrower window gives good ...
11 votes
3 answers
18k views

STFT: why overlapping the window?

For STFT, we impose window of certain size onto the original signal, then we perform fft on each window. The uncertanty about frequency and time is determined by the width of the window, however, I ...
2 votes
2 answers
123 views

How would you compute Fourier transform of a real world signal where the signal keeps getting updated (not a static one)?

Crossposted at Electrical Engineering SE A very naive question: How do we use Fourier transform for real world signals - for which you have the information only up to the present instant (and the ...
1 vote
1 answer
827 views

Using STFT as an input to a Neural Net

I'm trying to use the STFT as an input to a neural network. After flattening, there are over 4,000 features for a few seconds of audio. Is there a recommended way of summarising these to be a more ...
0 votes
1 answer
173 views

Best way to get the bin amplitudes of an audio DFT "normalized" 0-1

I'm working on a spectral processing plugin that's predicated on allowing the user to manipulate per-bin values in an STFT algorithm. I normalize the bin amplitudes by diving them by $N$ (number of ...
2 votes
2 answers
714 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
2 answers
1k views

Scipy and Matlab Spectrogram not matching

I am trying to replicate a spectrogram from MATLAB in Python. I've read other posts but they either don't use complex data or the data doesn't match between languages. I've defined my FFT length (<...
6 votes
1 answer
686 views

Equivalence between "windowed Fourier transform" and STFT as convolutions/filtering

I've heard, that "windowed Fourier transform" is but one perspective on STFT, and that STFT is fundamentally convolutions of windowed complex sinusoids with the input, i.e. bandpass ...
1 vote
1 answer
293 views

How do `n_fft` and `win_length` determine the window in spectrogram?

I am currently trying to understand librosa.feature.melspectrogram in a mathematical sense. In my understanding, spectrogram is based on the STFT which is for a ...
3 votes
2 answers
1k views

Amplitude extraction using STFT

I'm trying to recover amplitude/magnitude from an audio stream. I'm using FFT to go from time domain to frequency. If I feed in a signal of known amplitude, the results I get from either windowing or ...
1 vote
0 answers
28 views

Reconstruction of batch-acquired signal

I am currently working on a project which requires evaluating slow changes over time in the magnitude of a signal's high frequency (over 10 kHz) components. This signal was acquired in tests with a 25....
1 vote
0 answers
38 views

How to calculate phase estimation error

I am working on speech enhancement and I want to compare the phase and magnitude between two signals. I compute the STFT for both, and comparing the magnitudes is easy via mean-squared error or some ...
0 votes
2 answers
2k 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) ...
1 vote
0 answers
38 views

A mathematical justification of discontinuity detection using STFT

I'm trying to detect rapid changes in a one-dimensional signal say $[0,1]\ni t \mapsto f(t) \in [-1,1]$. By rapid changes, I mean corner points, edges, or sharp transitions at a point for example the ...
3 votes
5 answers
2k views

How to interpret the effect of different windows in short time fourier transform?

There are many categories of windows, e.g., rectangular, Gaussian, and triangular. What are their effects on STFT?
2 votes
3 answers
683 views

Does overlapping windows while processing a signal produce a stretched time domain?

I'm very new to signal processing and attempting to implement a spectrogram generator to learn more about DSP in general. So far, I have built up an understanding of how I might do that. Get input ...
2 votes
2 answers
1k views

Wigner-Ville Distribution (WVD) vs STFT for Spectral Analysis

What are the Pros and Cons of using Wigner-Ville Distribution for spectral analysis of a signal vs taking the STFT. When is it appropriate to use one over the other and is WVD used in real-time ...
8 votes
5 answers
13k views

What is really the Mel-filterbank?

After applying STFT to a signal, you typically need to convert the frequencies to the Mel scale. Typically the frequency values range from $0$ to $N/2$, where $N$ is the width of each sliding window. ...
0 votes
0 answers
232 views

difference in speed between tensorflow implementations of mfcc and stft

I am trying to preprocess audio clips for a keyword spotting task that uses machine learning models. The first step is to calculate the spectrogram starting from the waveform and in order to do so I ...
0 votes
0 answers
59 views

How to detect "buzz" components in audio by frequency domain analysis

I am trying to detect the amplitude, frequency and phase of the dominant "buzz" in an audio signal. By "buzz" I mean a periodic signal with sharp edges. For example, an impulse ...

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