# Tag Info

Accepted

### FFT to spectrum in decibel

Definitely you will have to calibrate your system. You need to know what is the relationship between dBFS (Decibel Full-Scale) and dB scale you want to measure. In case of digital microphones, you ...
• 11.1k

### What is first order difference?

The first-order difference operation is a technique for numerical differentiation. It is the simplest method that I know of, and consists of just treating a discrete-time signal as piecewise linear ...
• 24.6k
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### Advantage of STFT over wavelet transform

Wavelet transforms and short-term/short-time Fourier transforms are broad names for classes of transformations that are not totally distinct and may overlap (pun intended). Both can be efficient for ...
• 31.9k
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### Equivalence between "windowed Fourier transform" and STFT as convolutions/filtering

This answer isn't fully developed (but is correct), I may update in the future. Indeed, STFT is strided convolutions, and there's many practical caveats, discussed in this answer. Standard vs improved ...
• 8,913
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### Is "Windowed Fourier Transform" a synonym for "STFT"?

In Chapter 2.4 Previous Work of The Short Time Fourier Transform and Local Signals, S. Okamura, 2011, one reads: The STFT is also known under many names such as the windowed Fourier Transform, ...
• 31.9k
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### How to interpret the effect of different windows in short time fourier transform?

A window $w[n]$ truncates and weights (tapers) an input signal $x[n]$, to produce $v[n] = x[n]. w[n]$., for subsequent spectral analysis of $x[n]$. A windows's effect on the input signal's true ...
• 28.2k

### Window period(overlap) and FFT

In addition to what others have already said, I'll try to answer it from a purely practical point of view (this is also a variant of the overlap-add technique). If your FFT length is 2048, then an ...
• 921
Accepted

### STFT amplitude normalization, librosa library

I did answer a similar question a few years back, but can't find it. Basically, you are losing the energy because of the windowing. It's true to say that you should multiply the spectra by 2 in order ...
• 11.1k

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

What's going on? I think the main issue is the use of detrend='constant' in the calls to signal.periodogram. If I change that to ...
• 256

### FFT to spectrum in decibel

Some details to Jojek's post. Shared here for future reference. The key is to take the window in consideration and taking a reference ref which corresponds to ...

### Why is the name "Phase vocoder"?

The short-time Fourier transform (STFT) refers to the time-frequency representation of a signal, which is given by: $$X(\tau,\omega) = \int_{-\infty}^{\infty}x(t)w(t-\tau)e^{-j\omega t} \, dt$$ ...
• 304

### 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%. I'm sorry but you have a misunderstanding of spectral leakage in addition to how ...
• 28.2k

### Signal processing techniques for an accelerometer signal?

I'm wondering why the STFT pops out. To me, wouldn't a simple threshold on the signal itself or on its envelope do better / just as well, after removal of the g ...
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• 8,913

### What is the cause of STFT artifacts when different signals overlap?

Why does the STFT magnitude of this signal not equal the sum of the magnitudes of the individual parts? Because magnitude, i.e. complex modulus, is a nonlinearity:  |X| + |Y| = |a + jb| + |c + jd| \...
• 8,913

### Amplitude extraction using STFT

Firstly, STFT is fundamentally a time-frequency transform: convolutions with windowed complex sinusoids (i.e. bandpass filtering). You aren't going to "frequency", and "windowed Fourier ...
• 8,913

### Scipy and Matlab Spectrogram not matching

Itâ€™s a scaling problem, for which there are two options: Option 1: Use PSD scaling for both Python and Matlab Use mode='psd' in the ...
• 6,030
Accepted

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

Summary The problem is caused by detrend='constant' in the call to periodogram, which subtracts the mean of the input before ...
• 8,913

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

The most common method for time frequency analysis is the Short Term Fourier Transform (or STFT for short). Basically the input signal is chopped up into small chunks and then you perform a Fourier ...
• 44.6k