Questions tagged [stft]

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18 views

short time discrete fourier transform to detect time dependent changes in a frequency of interest & filter

I am working in matlab to compute the fourier relative phase of two signals as per https://sci-hub.tw/10.1123/jab.2017-0250 I have identified the fundamental frequency (f1) for the signals (1.7 Hz) ...
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3answers
50 views

How to generate a sinusoid with STFT at a frequency which is between bins

Is it possible to generate a sinusoid at a frequency which is between two bins (so a fractional index) with the STFT algorithm (by filling bins and doing the inverse) ? If yes then how can this be ...
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2answers
39 views

Why should one choose the maximum as reference for power-to-decibel conversion?

I have seen that one converts the amplitude to decibels through: $\text{dB(S)}=10 \text{log}_{10} \big(\text{S/ref}\big)$, where $\text{S}$ is the output of a STFT and ref the reference value for the ...
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1answer
22 views

Why is the number of frequencies decomposed in scipy.signal.stft() equal to the hop size?

I asked this over on StackOverflow first but figured you fine people might know more about signal processing (duh). I'm trying to calculate the spectrogram of an audio file in python. There's a nice ...
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1answer
31 views

What is the value range of log magnitude spectrograms?

I'm quite new to this field and have a probably rather basic question: Is there an upper bound for the values in a log-magnitude spectrogram generated like this: ...
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1answer
53 views

Advantage of applying a Window Function in Analysis and Synthesis of STFT?

I'm studying Short-time Fourier Transform and I learned that if you apply a windowing other than rectangular, you need to overlap the frames---for example, 50% overlap for Hamming family---to ...
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0answers
27 views

Synthesis of 75% Window Overlap Add method for Short-Time Fourier Transform (STFT)

I'm doing the overlap-add method for STFT and I quite understand the implementation if it's a 50% overlap (where I add the 2nd half of the previous frame to the 1st half of the current frame during ...
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1answer
30 views

Volume increase of a magnitude spectrogram

Let's say I have an audio waveform and I perform an STFT on the waveform and then take the absolute value to get the magnitude spectrogram. Is there a transformation that I can make to that ...
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0answers
23 views

Cannot reconstruct constant overlap add STFT perfectly

I am implementing an STFT function for spectrogram of certain audio files. Here's my function: ...
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0answers
27 views

How to create different Time frequency images from a data

I'm new to Python. I have a time series in a CSV file that has about 5000 rows and 3 columns. I have split the data into training and testing in ratio 70:30 respectively. However, I have a problem ...
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1answer
44 views

Given 1 recording of my voice, how can I process it to sound like 2 independent recordings of my voice played in unison?

I have one recording of my voice $x[n]$ singing a song. One thing I could do is independently record me singing the song again to obtain $y[n]$. Then, $z[n] = \frac{1}{2}\left(x[n] + y[n]\right)$ ...
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31 views

Mixing signal with noise in frequency space (STFT)

I am working on a preprocessing function which is supposed to mix two audio signals clean and noise in the context of neural ...
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2answers
33 views

Invertibility of Time-Dependent Fourier Transform

I am reading Oppenheim & Schafer's (O&S) Discrete Time Signal Processing (2nd or 3rd edition, does not matter) and I find hard to understand a technicality behind the Time-Dependent Fourier ...
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1answer
40 views

STFT to spectrogram

I would like to know whether I am correct in my understanding of going from STFT to a spectrogram. My goal is to convert a spectrogram back to a wav file. If I have my STFT: ...
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0answers
48 views

Clustering real and imaginary values within a frequency row of an STFT

I am analyzing a short audio .wav file of a drum and piano for source separation. (not using interpretable languages like Librosa, Scikit, Matlab, or R, but rather a compilable language in .NET). ...
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0answers
78 views

extracting mfccs after beamforming

I have a deep network for sound classification with mfccs as features. I wish to go through the process of beamforming before applying the classification. The original network uses ...
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1answer
38 views

Music source separation: Incomplete notation in published IS-NMF/EM pseudo-algorithm?

In a paper by Fevotte et al. on IS-NMF, which describes algorithms/implementation for multiplicative and EM variants of IS-NMF, the following algorithm is provided for IS-NMF/EM: In the algorithm's ...
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0answers
46 views

IFFT during ISTFT - and Nyquist

Using a compilable programming language (not Librosa, Matlab, etc), I am attempting to perform ISTFT on filtered (masked) source STFT matrices obtained from NMF. During the original construction of ...
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2answers
59 views

STFT window width vs. detectable Hz range

Assuming 44100 samples per second in a short 4-8 second-long audio .wav file, if I want perform FFT to detect the power spectrum, amplitude, and phase shift from 20 Hz to 10000 Hz (humans lose the ...
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1answer
57 views

Feature Extraction of Insect Sounds

First of all, forgive me if I sound stupid. I am still learning Audio Processing. So I am trying to make a machine learning model for detecting a specific insect through sound. Here is a sample raw ...
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0answers
26 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 ...
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0answers
43 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 ...
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0answers
18 views

Is it possible to restore audio that has been tonally modified by a phase vocoder?

My objective is to apply some process to the modified audio that allows me to obtain the original audio. I think it can be solved through machine learning techniques. I don't know if there is any ...
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1answer
87 views

Power Spectral Density of Finite Signals

I have a basic confusion which I hope someone can help clear. Say I have two signals: $S_1=\sin(2\pi t) \forall t\in[0,+\infty]$ $S_2=\sin(2\pi t) \forall t\in[2,5]$, $S_2=0$ otherwise Now let's ...
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1answer
106 views

Selected bin oscilation in STFT

I am looking for a noisy signal using STFT. My window length is 128 and I am using 75% overlap. I am using a Hanning window before running the FFT process. I am using Quinn's 2nd estimator for ...
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2answers
111 views

STFT on time varying signal with good time and frequency resolution

I am trying to determine the main frequency of a noisy signal that varies in frequency over time. Ideally I want to detect changes in the frequency as rapidly as possible - say 50Hz update rate, but I ...
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0answers
17 views

Estimate peak bandwidth from adjacent STFT bins for notch filter

I am using STFT to extract a strong, frequency varying signal from a continuous set of digital samples. I am able to do this very successfully and am determining the peak bin using PSD and 50% overlap ...
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2answers
103 views

Old style signal processing?

I am wondering if "an array of overlapping band-pass filters" it is 'mostly' equivalent to a Short-Time Fourier transform. See this (figure down), where $s(t)$ is the signal; LPF a second-order low-...
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1answer
72 views

Implementing MVDR beamformer in the STFT domain

I am trying to implement an MVDR beamformer for the first time. I was reading a couple of papers and books with many different notations and I am a bit confused. In my case, without loss of ...
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2answers
128 views

Multi Resolution STFT for audio

I am looking at trying to achieve a multi resolution STFT analysis on a log sine sweep audio measurement. I have an impulse, and I would like to perform two different windowed length FFTs on the ...
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1answer
68 views

STFT output frequency does not match sin wave frequency

I have the following function and pre definition for producing a sin and its' stft: ...
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1answer
78 views

CWT Disapointing Frequency Separation

I'm attempting to perform multi-resolution analysis via Continuous-Wavelet Transform (CWT) using Pywavelets. I've heard that CWT is supposed to be superior to STFT due to varying frequency content as ...
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1answer
202 views

Spectrogram Time Resolution with Overlap

I understand that the time resolution of a spectrogram with no overlap is the sampling frequency divided by the window length. How does this change with, say, 50% overlap? Does this double the time ...
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3answers
321 views

Does it make sense to use a wavelet that is equal to a sine of one period?

Would I get same results with STFT method (short-time Fourier transform) if I try this?
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0answers
31 views

When do phases not exist for spectrograms?

I have been reading a paper on the "Single pass spectrogram inversion" and I came across this in the Introduction part. In many applications, the analysis and modification of the Short-Time ...
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0answers
115 views

How to express STFT and ISTFT as a 1d convolution and 1d deconvolution in tensorflow/keras

I'm trying to implement this paper in tensorflow and keras. At the end of section 3 it says. ...
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0answers
22 views

Derivation of the reassigned STFT magnitude of a complex exponential

I have a complex exponential defined as $x(t)=Ae^{i2\pi f_{0}t}$ and its short time Fourier transform with respect to the analysis window, $g(t)$ is defined as, $$X_{g}(b,f) = \int_\mathbb{R} x(t+b)g(...
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0answers
332 views

Frequency range for STFT in Librosa

I am currently looking at the STFT for Librosa. I was wondering how to understand the output of the STFT function, specifically what kind of frequencies the different values represent. Say I have a ...
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1answer
220 views

Spectrogram power/magnitude normalization in analogy with image intensity normalization

In analogy with the 8-bit grayscale image color depth, in which the intensity of a sample pixel is normalized to a value between 0 and 255 by taking into account the minimum and maximum intensities ...
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1answer
36 views

How to pad a array representing music to pad the stft of this array?

I have an array named samples of size (2, 1321967) representing an audio file. When I pass it to scipy stft with ...
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1answer
95 views

How to deal with overlap in STFT when considering the highest energy among multiple channels

I have a 4 channels audio file. As a pre-processing step, it goes through an STFT with $T$ frames and $M$ frequencies. The output is divided into magnitude and phase per channel, so for $C$ channels, ...
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2answers
297 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 \|...
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0answers
18 views

Bandpass filtering with passband changing with time

Is it possible to implement some sort of filter which adapts as a function of time? Specifically, say I have a "noiseless" model of some signal which has the same frequency components at the same ...
2
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1answer
94 views

Frequency estimation on chaotic waveform

The target signal is generated by the following analytically solvable hybrid chaotic oscillator \begin{equation}\label{eq:1} \ddot{u} - 2\beta \dot{u} +(\omega^2+\beta^2)(u-s)=0 \end{equation} ...
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0answers
76 views

Scipy stft, how is shape of f determined?

Using scipy stft, like this : ...
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0answers
114 views

Find fundamental frequency in short time Fourier Transform

In an implementation of phase vocoder using Python, I found the author get an approximation of the fundamental frequency of STFT using the following formula: Freq0 = B/A * abs(B/A) where B is the ...
2
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1answer
223 views

How to set STFT-parameters to visualize woodpecker / Sawtooth Signal? ​

I always wanted to work with FFTs and Spectrograms to characterise sounds and their frequencies using python. Lately I recorded a woodpecker at his work. Woodpecker Wav File To know where to look ...
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1answer
62 views

How to classify the movement type of a target into two categories(direct motion or else) by using a doppler radar?

How to classify the movement type of a target just into two categories(one is direct motion which is almost straight line movement and the other is anything else) by using a doppler radar with a ...
2
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1answer
263 views

How to reduce synthesis artifacts produced by phase vocoder?

I implemented the phase vocoder algorithm in Python to time-stretch speech signals by following this paper and referring to this MATLAB tutorial. I can distinguish words in the original signal from ...
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2answers
707 views

How to calculate the PSD from the complex calculated STFT?

I have calculated the STFT with scipy python library: ...

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