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Questions tagged [spectrogram]

A spectrogram is a time-varying spectral representation (forming an image) that shows how the spectral density of a signal varies with time.

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2answers
3k 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 ...
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0answers
356 views

Smooth looking spectrogram display

I'm working on a simple sound analyzer application and a main feature of this program is the spectrogram display. I want this spectrogram to render fast and to be good looking while preserving all the ...
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2answers
282 views

Count the number of times the phone rings before its answered

I have a dataset of phone recordings that I'd like to do some characteristic-level analysis on. The audio is sampled at 44khz stereo, with each channel containing the signal from one party in a ...
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1answer
52 views

Should zero element be considered to calculate mean when smoothing spectrogram by window?

My (mass spectrometry) spectrogram does not measure the intensity constantly. I obtain the spectrogram, for example, ...
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2answers
501 views

Combining spectrograms with different windows to getting arbitrary time and frequency resolution

Spectrograms convert an amplitude-time signal into a frequency-time signal using Short Time Fourier Transform (STFT). The window size L used in STFT is a design choice. As L increases, you get higher ...
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2answers
323 views

How to deal with audio with different length in Audio Classification

Currently, I am trying to work with the Dataset UrbanSound8K to try some Audio classification. And I got stuck in the preprocessing step already. Since the audios are of different lengths, like 4 ...
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1answer
702 views

Analysing mp3 quality with spectrum, how to interpret the results?

When comparing spectrum images between two different audio sources in order to determine which has better quality, I sometimes come to an impasse. For example, consider the following images from two ...
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2answers
463 views

What is the amplitude range of a spectrogram?

Is there an upper and lower bound to a spectrogram representation of an audio signal? The range of the amplitude values of the audio signal is from 0 to 1.
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173 views

How to calculate spectrogram from nonstationary, nonuniformly sampled signal

I have a high resolution 3D spatial signal (xy-elevation data collected via Terrestrial Laser Scan) with very nonuniform sampling (holes/shadows due to vegetation; point spread varies as a function of ...
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2answers
693 views

how to use image filters for spectrograms?

Using MATLAB, I can import an audio signal and use some FFT function to get the spectrogram into the workspace. My question from here, is how to then process this spectrogram with image filtering ...
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0answers
493 views

calculating SNR from dbfs (using spectrograms)

I've the spectrogram of both noise and signal (both 5 seconds). Below image shows an example of the signal spectrogram: The colour of the spectrogram shows the intensity in dbfs (from 0 dbfs to -120 ...
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1answer
188 views

What is the spectrogram of an impulse response used for?

I saw that in acoustics an estimated impulse response of a room can be transformed using STFT/wavelets to a spectrogram as an analysis tool. However, I did not understand how the spectrogram is ...
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3answers
469 views

Why is the first axis of STFT frequency bin

When taking the STFT of an audio signal, the first axis is the frequency bins by convention, and the second axis is how it elapses through time. Is there a reason?
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78 views

Values (amplitudes) of the CWT and their relationship to waveform amplitudes?

I'm coding up a scalogram in C++. Right now it calculates a single row of the CWT matrix and immediately maps it to a line of pixels. Trouble is my colouring scales with the values of the transform ...
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2answers
372 views

Neural Network: Spectrogram Dimension

I like to work with a convolutional neural network in combination with a spectrogram as input. Assuming the spectrogram has the dimensions $T\times F$ (time$\times$frequency). Is it more natural to ...
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0answers
205 views

Help detecting target in pulsed radar signal

This signal is from the Pasternack $2.4\textrm{ GHz}$ development kit. The saved signal appears to be the pulsed waveform. It is sampled at $20\textrm{ kHz}$ for $4130$ points. I recorded a ...
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1answer
237 views

Do I need to bandpass filter the signal before applying the Zoom FFT algorithm?

Let's say I have an acoustic signal that I want to make a spectrogram of filled with broadband noise and tonals, sampled at oh, $44100\textrm{ kHz}$, and I want to zoom in on the band between $2600\...
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0answers
618 views

How does the size of a spectrogram relate to window length and frame rate?

I'm trying to understand the methodology from section 4 in this report about audio classification but I have some trouble understanding how they pre-process the data (dsp is not my area). $30$ ...
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0answers
118 views

difference between logged power spectrum and power spectrum?

What is the difference between a logged power spectrum and power spectrum... Well the log part. So can a normal power spectrum be converted to a logged power spectrum just by taking the log of the ...
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2answers
390 views

Does an equivalent transformation of a signal to a spectrogram image exist in which the phase information is part of the resulting image?

I'm working on a research project where we would like to apply convolutional neural networks to an image representation of a signal. However, it seems that if I would use a spectrogram, I would end up ...
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0answers
449 views

removing noise from audio

I have an audio file, in the range of 4 kHz to 120 kHz. I want to remove the lines that are not harmonic and are recognized as environment noise. the energy of the signal in this interval for each ...
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3answers
1k views

STFT multiplied with Gaussian window vs STFT multiplied by rectangular window

I am currently analysing my signal by looking at its spectrogram to determine the sinusoidal frequency content at the local sections of my signal overtime. I can do my spectrogram in 2 ways: Directly ...
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1answer
120 views

feature selection for classification for rare classes

I have a spectrogram of a signal and want to classify it. I used different features such as MFFC, the density of power spectrum and other common features and classify using the random forest, but I ...
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1answer
253 views

Unexpected peaks in spectral analysis

I am doing the spectral analysis of some antenna recorded signals by computing PSD (logarithmic absolute value of the FFT) and the spectrogram of the signal. The problem is that I get some unexpected ...
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0answers
70 views

Epoching Data with no Events in mne?

I am new to Python and signal processsing, and I'm trying to create a spectrogram of EEG data taken during a course of general anesthesia. I would like to use MNE's ...
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1answer
122 views

Extremely large reconstruction errors in NMF

First time in this stack... I am doing some audio analysis. I have a spectrogram ($N\approx 33000, M=1024$) and I need to run an NMF algorithm on it. I am using the Scikit learn implementation. And ...
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1answer
667 views

Reconstruction of audio signal from Spectrogram: Implementation

Is there somewhere an implementation available for the reconstruction of audio from a spectrogram? (e.g. based on this approach). I could not find anything, but I think there should be an ...
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284 views

Proper way of representing Static, delta, delta delta in a plot

I am currently working on recreating the result of this paper. The paper is about applying cnn in speech recognition, in which cnn is used to for feature extraction, for which a proper way of ...
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329 views

What is the autocorrelation equivalent of the spectrogram called?

I'm very knowledgeable about the differences between the Fourier transform, and the autocorrelation; mainly that one converts the time domain to the frequency domain, and the other finds periodicities ...
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1answer
121 views

Making a mesh out of the parameters from a STFT

I do not possess much knowledge about signal processing, so i hope to do a find an answer. I am reading a wav-file and then apply a fft on it. In theory, i think i have a 3 parameters i can use. Time ...
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1answer
1k views

What is the instantaneous frequency of this signal

Suppose we have the signal $x(t) = \cos(\pi t) + \cos(\pi t^2) + \cos(\pi \cos(\pi t))$ How can I find the formula which gives the instantaneous frequency $f(t)$?
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1answer
317 views

Time-Frequency Analysis of Big Data - Data Size Reduction: averaging the most appropriate method?

Explanation: I would like to analyse the data from an experiment, which investigates the performance of a mechanical component using sensors, that has generated 2000 CSV files. Each file contains 513 ...
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1answer
273 views

Raw speech data into spectrogram

I am using Delphi trying to make a very simple speech recognition system. The system collects raw data well, but I have a hard time turning the data into a spectrogram: The system collects an array ...
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1answer
345 views

Digital Camera Spectroscopy?

Would it be possible to use a conventional Canon DSLR camera to do some kind of vaguely meaningful spectrum analysis with GNU Octave? My niece needs to do a biology science project for school so I ...
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1answer
275 views

Difference between spectrogram and a figure in an audio signal

i wrote a function in MATLAB which will divide a audio waveform (a speech) into smaller windows with overlap .The output will be a matrix X, each column of which contains the windows which i export. ...
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1answer
2k views

Spectrograms for neural nets

General Question Given an audio file, say a 16-bit wav, what are some standard methods to preprocess a spectrogram of this wav so that it may be fed into a neural net? Context In Lee et al's 2009 ...
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1answer
119 views

Could not construct original matrix using SVD

I need to read a .wav file make a 2D matrix from it using the STFT generate its singular value decomposition do some watermarking but I can't build the original ...
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1answer
1k views

What is Causing a Cyclic 1kHz Noise Signal in Audio Recording?

I dug my old Behringer UCA202 out of my shed and plugged it into a computer. I did some tests and it appears to be working fine... apart from some noise signals on the line input channels. I'm not ...
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2answers
2k views

FFT spectrogram in log frequency space. How?

I was reading a paper and the authors say that they extract FFT spectrograms and log-scale in frequency domain. I understand how the general spectrogram is computed, but how to make it log-scale in ...
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1answer
3k views

Spectrogram for created signal in Octave

I'm trying to test the specgram function located in the signal package in octave but I'm a little confused at the variables in ...
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1answer
386 views

unexplainable aliases in spectrogram

My scope has 200 MHz bandwidth and can sample at 4GS/s I'm sampling a 138 MHz RF signal at 500 M Sa/s storing 14 M points. When I plot the spectogram in matlab I get the following spectrogram(Data,...
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2answers
161 views

Reduce “flicker” in spectrum analysis / spectrogram

I'm performing a series of FFTs on windowed extracts of an input signal, to get a frequency spectrum over time. This is for a visualisation - I'd like to keep the window small, so the visualisation ...
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3answers
2k views

How to interpret spectrogram correctly?

I have a pressure transducer signal from a reacting mixture available here, which has a sampling frequency of 50kHZ. I have also obtained the spectrogram of the signal with NFFT=256, noverlap=4 as ...
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1answer
594 views

Is this waterfall characteristic of QAM or OFDM (or something other) modulation?

I recorded this signal at 2.45GHz, it is coming from a camera. Is this QAM or OFDM ? Based on those side-lobes I would guess OFDM but I am not sure. Also there seems to be an interesting preamble ...
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1answer
581 views

Why is the DFT used for spectrograms rather than the DCT?

Related to Could a DCT be used for an audio magnitude spectrum rather than DFT?, but more on the (audio) spectrogram side of things I've been reading about the DCT (such as from here) and it ...
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1answer
2k views

Recovering phase from spectrogram

In this answer, an iterative algorithm is given for recovering a signal from its spectrogram, assuming overlapping windows: $$ x_{n+1} = \operatorname{istft}(S \cdot \exp(i \cdot \operatorname{angle}(...
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1answer
457 views

Principal Component Analysis as a step between STFT and MFCC

For computing Mel Frequency Cepstral Coefficients you can use already calculated STFTs as a basis and perform the Mel frequency mapping on it. My question: Does it make a significant difference if I ...
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1answer
805 views

Obtain the frequency response of a time domain chirp signal

I have simulation data in the time domain and I need to represent them in the frequency domain. The data have been obtained time integrating the following equation: $m \ddot{x} + c\dot{x} + kx = A \...
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4answers
46k views

How do I plot the spectrogram of a wav file?

I am dabbing a little bit into signal processing on MATLAB. And I have the following question that I would like to know the answer to. What has to be done : Plot the Spectrogram of an audio file. ...
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2answers
190 views

Meaning of concentric circles on the spectrogram

I've got this unusual spectrogram and I am really curious what these circles could mean. Has anyone ever seen anything like this? What could be the source of the signal?