# Questions tagged [stft]

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### 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
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### 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 ...
39 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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### 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 ...
71 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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81 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 ...
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1 vote
102 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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### 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
85 views

### Reconstructing Audio From Spectrogram (Using it as a filter)

Given a spectrogram calculated using the following code: ...
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106 views

### normalize STFT output by magnitude

I am using torch.stft() to generate spectrograms for neural networks and come across the below code. ...
• 45
1 vote
32 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 ...
• 279
134 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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### 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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### 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 ...
83 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 ...
139 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
65 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 ...
32 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)?
213 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 ...
91 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 ...
85 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 ...
765 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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65 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
154 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 ...
93 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
69 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 ...
298 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 ...
1 vote
89 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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70 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 ...
455 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: ...
396 views

90 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
87 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 ...
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1 vote
544 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 ...
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### 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 ...
113 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 ...
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### 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
191 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 ...
2k 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
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 ...
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185 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 ...
120 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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271 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 ...
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44 views

### Coherence for order spectra

The scipy signal coherence function computes for two time series the coherence as a function of the frequency. For rotating systems however, it is sometimes meaningful to analyze the two recorded ...
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64 views

### Spectrogram without using stft

Can I use any kind of transform to make spectrogram, not just stft? Is it possible to get the spectrograms of a signal without using stft? What difference does it make if I calculate the frequency ...
44 views

### Stft of sinusoids

I have a sinusoidal signal of 10 minutes. For the first 5 minutes, the signal has a frequency of 100 Hz and for the next 5 minutes, the signal has a frequency of 200 Hz. 1 - If I look at the ...
204 views

### Synchrosqueezed STFT phase transform

Synchrosqueezed STFT paper, Synchrosqueezing based Recovery of Instantaneous Frequency from Nonuniform Samples, defines STFT phase transform as:  w(u, \xi) = \xi - \frac{\partial_tS_{g}f(u, \xi)}{j2\...
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### Do i need to remove mean in STFT when working on music audio?

i need to apply a STFT to some music audio files but i can't understand if i should remove the mean or not. I know that for stochastic signals that is a must and that sometimes also necessary for ...