Questions tagged [stft]

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11
votes
4answers
4k views

What's the difference between the Gabor-Morlet wavelet transform and the constant-Q transform?

At a glance, the constant-Q fourier transform and the complex Gabor-Morlet wavelet transform seem the same. Both are time-frequency representations, based on constant-Q filters, windowed sinusoids, ...
3
votes
3answers
684 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
0answers
259 views

Segment/Idenfication of signal from a spectrogram

I have the following Spectrogram of a signal: Essentially, in this signal, I know there is one point of interest (between 60-80) and between the the particular frequencies. I could, potentially ...
1
vote
2answers
204 views

What is the advantage of overlapping windows while evaluating Spectrogram?

I've seen many documents that refer to calculate spectrogram through overlapping windows but haven't found clear documents on why this is done and how to calculate the number of points that need to be ...
6
votes
1answer
14k 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 ...
5
votes
4answers
15k views

Choosing the right overlap for a window function

On Wikipedia there is quite a list of window functions. However, when you are doing a lot of STFTs, you often have to have some overlap to get better results. Generally an overlap factor of 2 (i.e., ...
5
votes
3answers
41k views

FFT to spectrum in decibel

Here is a 10 seconds-long 440hz sine wave normalized at $0\textrm{ dBFS}$. When computing the STFT (with the code below) of this audio file, I noticed that ...
4
votes
2answers
683 views

STFT calculation with Gaussian Window

$$ f(t)=\exp(jat^2) \,\,\, and \,\,\, g(t)\,\,is\,\, a\,\, Gaussian\,\, Window:$$ $$ g(t)= \left (πσ^2\right)^{\frac{-1}{4}}\exp\left (\frac{-t^2}{2σ^2} \right ) , \,\,\,\,\,\,\left \|g(t) \right \|=...
0
votes
2answers
4k views

Wav To Spectrogram, Back To Wav

Currently, I'm writing a Python script, which should do the following: read an audio file respectively a wav file via scipy.io.wavfile.read(). calculate the spectrogram of given wav file. write the ...
12
votes
3answers
5k 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 ...
22
votes
2answers
10k views

Inverse Short Time Fourier Transform algorithm described in words

I'm trying to conceptually understand what is happening when the forward and inverse Short Time Fourier Transforms (STFT) are applied to a discrete time-domain signal. I've found the classic paper by ...
14
votes
1answer
15k views

Comparison between Fourier transform, short-time Fourier transform and wavelets

What is the difference between the Fourier transform, short-time Fourier transform and wavelets?
12
votes
4answers
16k views

Can you increase frequency resolution of FFT without increasing window size?

I'd like to use STFT for multipitch analysis. I realise detecting the partials existing in the signal is just the beginning. Still I have problem with it. Let's say I have signal sampled with 'CD' ...
4
votes
3answers
3k views

Filtering with STFT

I have sucessfully implemented a STFT (+inverseSTFT with perfect reconstruction of original signal, with overlap add, etc.) in order to work on audio files. Using this STFT / iSTFT framework, I have ...
1
vote
3answers
12k views

Window period(overlap) and FFT

How does changing the window period (i.e the number of points overlap between two frames) affect the FFT results ? Suppose that a time series signal was converted to frequency domain by FFT with ...
16
votes
5answers
15k views

How do I optimize the window lengths in STFT?

I have many EEG signals and I want to analyze them using linear methods such as STFT (Short Time Fourier Transform). In STFT , How can I optimize the analysis window length, to reflect the frequency ...
10
votes
1answer
3k views

What is the maximal frequency resolution for Matlab's STFT implementation spectrogram()?

Matlab's spectrogram() function calculates the STFT of a signal. It describes its NFFT argument as follows: ...
8
votes
2answers
1k views

Signal processing techniques for an accelerometer signal?

I am running some tests where I am recording accelerometer measurements. I am looking to use elements of signal processing on this signal, but I am unsure about where to begin, or what my approach ...
8
votes
3answers
406 views

How critical is the selection of the window function in STFTs?

I have a sum of periodic signals that I am trying to untangle using time-frequency analysis. I seem to get wildly different results depending on the window length and shape. This is a problem because ...
4
votes
3answers
8k views

Understanding overlapping in STFT

I understand the concept of the STFT. In order to avoid spectral leakage, you use a Hann window that overlaps by 50%. However, the problem that I have, is that the example code online does not account ...
2
votes
1answer
3k views

length of window and overlap rate in STFT

I want to use STFT to analyze my signal and am wondering what are differences between two solutions: Use short windows (for ex. 256 samples window) Use longer windows (to get higher resolution in ...
2
votes
1answer
73 views

Window with optimal sidelobes for a given ENBW / frequency-resolution

Is there a family of windows which is "optimal" in terms of energy above/below a boundary, but with controllable ENBW/bandwidth? By optimal, I mean maximising energy concentration inside ...
1
vote
0answers
298 views

Zero STFT bins (and not FFT bins)

Filtering by taking FFT, zeroing bins, and inverse FFT is a bad idea, as discussed here. But what about: take a STFT, (i.e. multiply the input signal by moving window function, and take FFT) zero ...
1
vote
2answers
545 views

Short-time Fourier transform Tradeoffs

In the Short-time Fourier transform what are the tradeoffs between different: window functions window lengths sample rates
2
votes
1answer
1k views

Should I ever pick the continuous wavelet transform over the discrete one? DWT vs CWT vs STFT

Of course I mean in terms of numerical algorithms. I'm reading various papers on the wavelet transform and why it's better than the short-time Fourier one. The reason that's cited more often is that ...
1
vote
1answer
1k views

How do I find the power of a specific frequency at a specific sample of a discrete time varying signal?

EDIT: First off let me explain that I understand that frequency makes no sense for a single sample. What I am actually talking about is the power spectrum within a short time window around a specific ...
3
votes
2answers
4k views

Meaning of Hop-Size in Filter Bank Interpretation of Short Term Fourier Transform

The Short Term Fourier Transform (STFT) is used to obtain the time-varying spectrum from a signal. There are two ways to understand it - the overlap add interpretation, and the filter bank ...
3
votes
0answers
432 views

Why are the frequencies associated with the STFT bins not representative of the energy?

I'm experimenting with a 30 Hz sine wave and I want to extract the frequencies of this, and have implemented the algorithm to do so. This gives a correct reading, well, gives 29 Hz. I'm now wanting ...
2
votes
3answers
7k views

Librosa stft + istft - Understanding my output (which always seems too perfect) at varying window lengths

I've just started to use Python with Librosa for a DSP project I'll be working on. First thing I've been trying to do is determine my preferred parameters for the FFT window size, and hop-distance. ...
2
votes
3answers
3k views

What is the relation between windowing and hopping in audio DSP

While using short-time Fourier transform (STFT), it is common to use window function, usually tapered. Will this not alter the original signal $x[n]$ and the STFT may no more be the true STFT of $x[...
1
vote
2answers
120 views

STFT with varying window lengths (like the continuous wavelet transform)

I was wondering if it is possible to use windows of varying lengths when making a spectrogram based on the short-time Fourier transform (STFT). That is, for higher frequencies I would use shorter ...
1
vote
1answer
936 views

Shift property of the Short-term Fourier transform (STFT)

Properties of STFT (Short-term Fourier transform) say that it preserves time shift up to modulation. Does it mean it is sensitive to time-shift in signal?
1
vote
0answers
56 views

How to deal with phase incoherence issues after manipulating a signal in the frequency domain?

Let's say that we want to manipulate a signal in the frequency domain using a short time Fourier transform and once we're done , we use an inverse STFT (plus overlap and save) to convert the results ...
1
vote
1answer
1k views

Computing narrowband spectrograms using MATLAB [closed]

I'm having an assignment of computing narrowband spectrograms using MATLAB. And I totally have no idea about the code. Can someone help me writing the code and explaining what's going on to me. Lots ...
1
vote
0answers
48 views

Modified STFT resynthesis

This post is basically a follow-up to my recent question, which I asked here How to deal with phase incoherence issues after manipulating a signal in the frequency domain? In short, I'm modifying the ...