Questions tagged [stft]

Short-Time Fourier Transform

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32 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
51 views

Choice of relationship between n_fft and window_length in STFT

Not a veteran in Signal Processing, it would be extremely appreciated to help me understand the idea/heuristic behinde the idea in STFT that $$\text{nfft} \ge \text{window length}$$ At least from a ...
3 votes
2 answers
233 views

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

I'm trying to learn about why signals that cross in an STFT cause apparent artifacts in the magnitude. I've been looking at the example below, written in python, where a gaussian peak overlaps with a ...
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1 vote
0 answers
38 views

STFT for Classification

I am working on this project in which I am using Short Time Fourier Transform (STFT) for feature extraction before applying classification model. I have a time series sensor data, applied signal ...
0 votes
1 answer
50 views

Why does varying n_fft change the range of x axis values when plotting STFT?

I am using librosa.stft to apply an STFT to an audio sample and display a spectogram of the results when using different sampling windows (...
0 votes
1 answer
57 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
1 answer
51 views

Spectrogram of a shock event

I have measured data of a vibration with chirp input were I suspect unwanted shock events occurred. I therefore thought about computing the spectrogram of my time histories to check the frequency ...
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1 vote
1 answer
55 views

Filterbank Interpretation of Inverse STFT With Hop

The slide below, borrowed from CMU, shows the typical interpretation of the "filterbank interpretation" of signal reconstruction from a Short Time Fourier Transform. As far as I can tell, ...
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2 votes
2 answers
147 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 ...
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1 vote
0 answers
113 views

How to create overlapping frames of input signal for stft using HDL coder for FPGA implementation?

I want to implement stft on FPGA. For this purpose I use HDL coder and the problem is I have no idea how to create overlapping frames of data for further FFT. In my example I want to use 256 frame ...
0 votes
2 answers
84 views

Impact of STFT window function and FFT length on computation time

I have been doing a study which part of it includes a comparison of computation time vs window type and length (among some other things in the computation time, however I speak in terms of relative ...
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0 votes
1 answer
69 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
1 answer
143 views

Performing STFT after Butterworth Filter Seems Lower in Resolution

I have a signal recorded at 2MHz sampling rate. Before any decimation might be required, I first looked for peaks in my periodic recorded signal using STFT/spectrogram. From here, I can clearly see ...
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0 votes
1 answer
133 views

Calculating Short Time Fourier Transform Manually

I am doing a project on short time Fourier transform, I have to perform STFT for 128 data points. I have developed a Matlab code to perform the STFT operation. But, my main concern is, I need to ...
1 vote
1 answer
112 views

Classifying STFT from multiple signal samples

I have a collection of signals (IQ wav) split up into ~2s samples of sampling rate 2MHz, and can collect the STFT information from these samples through the following code: ...
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3 answers
141 views

Is it possible to classify signal samples using STFT without (image-based) spectrograms?

I am aiming to conduct a classification-based study using signals collected from various devices. I've researched other approaches which make use of STFT for producing a spectrogram for speech and EEG/...
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1 vote
2 answers
209 views

Reconstructing Audio From Spectrogram (Using it as a filter)

Given a spectrogram calculated using the following code: ...
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1 answer
217 views

normalize STFT output by magnitude

I am using torch.stft() to generate spectrograms for neural networks and come across the below code. ...
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1 vote
0 answers
68 views

Strong vs weak COLA (constant overlap-add)

My question is on the aliasing cancellation of the OLA method when spectral modification is involved. The book related to this question is given by this link. As stated by the webpage, for weak COLA ...
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3 votes
2 answers
176 views

Optimize window length (STFT) via gradient descent (in neural networks)

The authors from this paper optimized a Gaussian window size via gradient descent (the σ parameter of the bell curve) together with the other parameters of neural networks. I don't use Gaussian window ...
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0 votes
1 answer
25 views

Calculate number of buzzs and their duration

I'm trying to calculate the number of buzzs and their duration from a buzzer. I'm working with python and scipy lib and the short time fourier transformation capturing the audio with a microphone. To ...
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0 votes
1 answer
151 views

How to zero pad and do overlapping block convolution to reconstruct audio for frequency filtering in time-frequency domain

I am doing STFT (short-time Fourier transform) on real-time audio to filter frequencies by magnitudes (to reduce noise) which have certain drawbacks like noise spikes in reconstructed audio in the ...
2 votes
2 answers
125 views

Inverse STFT causing unwanted noise spikes?

I have an (audio) signal. I am applying STFT continuously and after applying a certain magnitude threshold I am doing inverse STFT to reconstruct the signal. But I am getting some unwanted mini noise ...
3 votes
1 answer
200 views

Detecting background noise from audio time-freq domain analysis

I have a requirement to detect/reduce sidetalk/background noise in real-time audio. I am stuck in how can I detect this from audio time-frequency domain analysis. I am already getting the time-freq ...
1 vote
0 answers
114 views

Confusion regarding STFT phase vocoder-based pitch shifting

I'm currently working on a phase vocoder implementation based on the Short-Time Fourier Transform; it's heavily based on the models described here and here. I have successfully completed the analysis ...
-1 votes
1 answer
73 views

The effect of doubling the sample rate in Spectrogram

If we have an audio file and we only change the sample rate (double it), what changes our spectrogram will have (after using the stft)?
5 votes
3 answers
401 views

Role of window length and overlap in uncertainty principle?

I am trying to predict epilepsy using spectrograms and a convolutional neural network. So far I have achieved a validation accuracy of 86% which i feel like is pretty good. Lots of the papers doing ...
0 votes
1 answer
222 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 autoencoders. I feed the reverbered spectrogram to ...
0 votes
0 answers
255 views

Spectrogram normalizaion to train a Fully Convolutional Model for Audio dereverberation

I'm trying to implement a deep learning based dereverberation algorithm. The network I am using is inspired by the U-net. The idea is to supply the reverberated spectrogram as input and 'clean' it ...
8 votes
4 answers
1k views

Advantage of STFT over wavelet transform

I have learned about STFT and wavelet transform recently, and wavelet transform seems better than STFT in my opinion. So, I wonder if there is any advantage of using STFT than WT, and if so, what are ...
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2 votes
1 answer
73 views

Understanding stability in frame theory. Wavelets

I'm trying to grasp some understanding of the concept of stability in the context of the frame theory. The definition of frame in ref1 states that a sequence of functions $\{ \phi_n \}_{n \in \Gamma}$ ...
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1 vote
1 answer
454 views

Hop size in STFT

I am reading the documentation of scipy.signal.stft function: https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.stft.html#scipy.signal.stft. My question: is the 'noverlap' parameter of ...
2 votes
1 answer
112 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 ...
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1 vote
1 answer
76 views

Should i use window with hop_size in Wavelet Transform or Discrete Wavelet Transform?

I have a signal (audio - voice) with 1 second of duration with sample rate of 50000 Hz. It is big signal and I wish extract some features and apply pattern recognition or classification. My question ...
-1 votes
1 answer
431 views

How to specify parameters in scipy.stft to reproduce published analysis

I am starting a project on this Keggle dataset containing EEG registrations (sampled at 128 Hz) of several subjects. What I am really interested in is the final ...
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1 vote
2 answers
94 views

How to objectively measure how "good" a time-frequency representation of music is?

I've been studying the time-frequency uncertainty principle of Dennis Gabor, and the tradeoff of the STFT window size in representing the tonal and transient characteristics of the musical signal ...
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0 votes
0 answers
92 views

Mapping STFT magnitude to sound intensity level

I have a signal for which I have computed my STFT magnitude spectrum in dB. The plot is the following: This is my magnitude spectrum in dB computed with ...
3 votes
3 answers
714 views

scipy.signal.spectrogram() - how to handle gaps in the timeseries data

Looking at the magnitude of variable stars - the dataset is from here: https://dogwood.physics.mcmaster.ca/Cepheid/URL/MW/BD-10d4669.html The magnitude plot: ...
0 votes
1 answer
589 views

scipy.signal.spectrogram() with noverlap=nperseg-1, what are the possible side-effects?

I'm using a simulated data set which can be downloaded from the link in the fist paragraph on this page (it's an Excel file): https://www.analyticbridge.datasciencecentral.com/forum/topics/challenge-...
-1 votes
1 answer
124 views

scipy.signal.stft temporal resolution

Using the STFT function from scipy.signal has produced unexpected results for me. I am performing an STFT on 10 seconds of data, sampled at 25,000 Hz. I am using STFT settings of nperseg=256 and ...
1 vote
0 answers
91 views

Wrong amplitude in the FFT for 10 seconds measured signal

I measured a signal with the Osziliscope that I generated with a signal generator. The signal is a pure sine wave with a frequency of 1 kHz and a peak amplitude of 2.5 V, I measured the signal for ...
1 vote
2 answers
841 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 ...
0 votes
3 answers
101 views

Why Matlab Spectrogram of slow and rarely sampled signal shows high frequencies

I have a signal, which was measured for 14.4 minutes (= 864 seconds). There are 192 measurements, so one measurement was done in every 4.5 seconds, which results in a 0.22 Hz sampling frequency if I ...
2 votes
1 answer
121 views

Biorthogonal Windows

I am starting to study about the concept of biorthogonal windows and the relation to (Discrete) Fourier transform and short-time Fourier transform (STFT). I have not found an introductionary review of ...
0 votes
3 answers
212 views

How Short-time Fourier transform (STFT) is different from from filtering?

If we want to know frequencies in a signal over time I know we can use Short-time Fourier transform (STFT). but I read in a paper "The spectrogram representation was obtained by first filtering ...
1 vote
2 answers
251 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 ...
4 votes
4 answers
4k 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. ...
1 vote
0 answers
50 views

Short Time Fourier Transform has different frequencies than Fourier Transform?

The reason we do the STFT is so that we can analyse for short segments of time how much of the components in the frequencies of the FT are present. However, it may be possible that completely ...
3 votes
2 answers
219 views

Why does Matlab spectrogram look stripy when windowed input is zero-padded?

I am working on a little project, and stumpled upon something I cannot understand yet. I am learning cognitive science, and don't have DSP knowledge background, only learning from what I find on the ...
0 votes
0 answers
236 views

Efficient STFT computation

I am calculating the STFT using scipy, and then reducing it in size, flattening and then normalising it. Code is below. It's incredibly slow, given I'm trying to ...
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