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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zeros in audio material

I have a question about spectogram. I have an imported audio file of 15 seconds (file from music CD). Before i make my own stft script and 3D plot i tested a the standard spectogram function. This ...
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41 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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87 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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43 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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37 views

Wavelets vs FFT based spectrogram for RF signal identification/analysis

What are the advantages / disadvantages of using a Wavelet based spectrogram vs an FFT based spectrogram (as shown by Baudline, for example) for RF signal analysis / identification ? This paper seems ...
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123 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
102 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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75 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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87 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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2answers
115 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?
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1answer
86 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
85 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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132 views

How can create a .wav bar based spectrogram on matlab?

How can I create a bar based spectrogram that updates as a .wav file is playing. This is commonly found in music players. Here is an example below: I am able to display a amplitude/frequency graph ...
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62 views

What are best practices to compute an audio spectrogram?

The spectrogram if generally defined with the squared magnitude of the fft. However, in lots of implementation, it seems that people just use the magnitude without square. Moreover an audio signal is ...
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1answer
47 views

Voss algorithm and pink noise

the voss' algorithm generated a 1/f series. What does the series mean? For example, we use three dice and the result sequence length is 8. Let's set the sequence is 8,15,6,9,14,10,9,7. Then what does ...
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2answers
138 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
61 views

How to compare the syllable extracted from the audio

I need to recognize just one bird. I am trying to compare the syllables extracted from the sound samples. As a result of the spectrogram function, the power spectral density is taken from the sound. ...
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2answers
268 views

Frequency Spectrum with c++

I have written a script to plot the frequency spectrum of a sinusoidal signal with c++. Here are the steps 1-Applying Hanning window 2-Apply FFT using fftw3 library I have three graphs: Signal, Signal ...
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1answer
204 views

Spectrogram, time vs frequency localization, and length of signal

So I'm having some trouble conceptually and am hoping somebody can clear something up for me. This is long and I apologize for that but I want to provide as much information as possible so that the ...
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47 views

Time domain sweep function to frequency domain

I have an input sweep sinusoidal signal (constant magnitude sweeping the frequency range of 0.1 to 25 Hz) to my mechanical system. My question is that to analyze the output signal as an acceleration ...
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1answer
584 views

Python - time frequency spectrogram

I have some 64 channel EEG data sampled at 256Hz and I'm trying to conduct a time frequency analysis for each channel and plot a spectrogram. The data is stored in a numpy 3d array, where one of the ...
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47 views

Frequency range of acoustic feedback

What is the frequency range in which acoustic feedback can be found? Most importantly, is there some lowest frequency below which one can expect not to find any feedback? My conclusion from the ...
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1answer
96 views

Why does the specgram of this simple sine wave look strange?

I'm trying to test some intuition using the matplotlib specgram routine. I first generate a simple sine wave ...
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1answer
34 views

could not constract original matrix with matlab svd's function

I need to read a .wav file, make a 2D matrix from it using stft, generate singular value decomposition of it using svd method and do some watermarkings... but I can't build the original matrix again ...
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1answer
81 views

Extracting original signal from overlapping area

Considering this image, where I have a spectral decomposition of a light bulb. Due to the non point shaped light source, the spectral decomposition using a diffraction grating in front of my camera ...
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1answer
57 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: ...
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3answers
181 views

Drawing a Spectrogram off of FFT - what are the decibels relative to?

I am trying to draw a spectrogram from FFT data I get from audio files. The problem is that I can't figure out is what the yielded power (decibels) are relative to. I'm getting some arbitrary -100db-...
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49 views

Are there any pictures of a sample accurate spectrogram on the web or in books?

I programmed a sample accurate spectrogram some time ago and i still have never seen a picture of another one. It's interesting maths, i was told it's trivial, so why has no one else posted research ...
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1answer
308 views

What is the most precise frequency analysis spectrography algorythm?

Everyone uses Fast Fourier Transform, which is fast at the detriment of precision. The input audio has sample accuracy and the FFT has 1/64 sample accuracy. What algorithms can output high resolution ...
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1answer
84 views

Matlab: is a highpass filter what I want, to obtain my required spectrogram? How do I design/apply this? (pic included)

The axes are wrong in the spectrogram. I have an audio wav file, and I know the sampling rate. this is read into the audioData variable. The audio is 1 channel. selected window length I believe (can't ...
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161 views

Converting musicg spectrogram output to dBFS

I'm trying to convert musicg Spectrogram output to dBFS. With 16-bit signed integer PCM audio, and an FFT length of 2048, I'm trying to analyze the spectrogram for an audio file to determine things ...
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1answer
178 views

Strange phase spectrum from stft

I've tried to implement STFT in functional way in Python. I've got code such as below: ...
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2answers
265 views

Spectrogram of a chirp and its FFT

This question follows from an answer to this other question: Conceptual question on FFT and chirp signal I wrote a code starting from the spectrogram to compare it with the FFT result. ...
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1answer
56 views

Developing a classifier for a periodic music

I am trying to develop a classifier for Indian Taals, for which I would be focusing only on the Tabla. Now once a extract a period of the Tala(a repetitive pattern), I want to develop some feature ...
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147 views

Choosing the best measure for machine learning on a Spectrogram

I am working on an application to classify Talas(a piece of music with onsets). For that, I have the spectrogram of a Tala, which I want to compare with the test Tala, or compare 2 Talas. For this I ...
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1answer
991 views

Reconstructing time domain signal with Hanning window

I am currently working on a frequency domain real-time application on a digital signal processor. Currently for one time frame of my algorithm I read in time domain data into a buffer, perform a ...
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44 views

Can uneven sampled points generate valid PSD and spectrogram?

My recording device samples signal at 100 Hz. At each sampling point, it generates 512 values (I assume due to non-ideal impulse in practice, so each impulse is actually a window with certain width ...
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3answers
224 views

Rendering a spectrogram of audio data - resulting magnitudes are all too close together

I'm working on creating an application which will render a spectrogram of the audio in an MP3 file. I'm having some trouble, though - after running the audio samples through my program, the resulting ...
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123 views

Looking for an algorithm that computes weighted average of frequencies intensity from narrow band in spectrograph

I am searching for the algorithm that takes (audio) signal as an input and outputs weighted intensity of the frequencies of some narrow band (axis X) in time (axis Y). Frequency in the middle of that ...
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1answer
56 views

Frequency resolution

I have made a stft_func in MATLAB which takes window length i.e t_short as a parameter for window length. Now, this function is ...
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1answer
109 views

Given a spectrogram, how do I calculate loudness over time?

I want to calculate the loudness of a given sound over time (like, in a graph) from its spectrogram. Can I do this from the spectrogram or is it better to do from the raw sound?
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1answer
323 views

Improve spectrogram appearance using windowing functions MATLAB

I have a program which plots data obtained in a NI USB DAQ realtime to a spectrogram plot using the surf function. I'd like to improve the appearance of the plot using some sort of windowing function. ...
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109 views

Understanding PCA

OK, I have tried to ask the same question in the math site on stack exchange but no real joy. Apologises I'd this is the wrong forum. I am trying to compute the PCA of a spectrogram.. It is 486x128 ...
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1answer
93 views

Detecting a curve with certain characteristics in a spectrogram

I have a spectrogram built by breaking a signal into chunks and taking the FFT of these chunks. An example spectrogram is: In this spectrogram I am looking for a curve (aka pitch contour) that: ...
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1answer
125 views

How to obtain the Spectrogram of a signal

I am trying to use Matlab to compute the spectrogram of a signal but I can't seem to figure out how Matlab computes the spectrogram.Consider the case where I have a ...
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1answer
567 views

PSD - Is this formula correct?

Trying to understand whether or not I am calculating the PSD correctly. Below is the equation that I am using: $$ PSD_{rms}(f_{m} = m \cdot f_{res}) = \frac{PS_{rms} }{ENBW} = \frac{2 \cdot \left | ...
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2answers
463 views

Spectrogram - Am I missing something?

I have the following signal: I'm trying to compute a Spectrogram algorithm, but, don't think I'm doing it right.. I have computed the following: 1) STFT (size 256 with an overlap of 128) 2) ...
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3answers
238 views

Will the resulting spectrogram from this algorithm be 1D or 2D?

I'm implementing a spectrogram algorithm and I get the basic concepts, however, I'm struggling with something. Let's say I have a 1D vector: ...
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3answers
826 views

Why do we get ripples in the frequency spectrum of a chirp, and how do I remove it?

The ripples in the amplitude spectrum of a linear spectrum is undesirable. I desire to obtain a flat spectrum response. Hence, how can I remove these ripples? Also, which factors (like time bandwidth ...
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2answers
2k views

Get spectrogram matrix without specgram in MatLab

I have a signal in Malab, and I need a matrix, probably transposed specgram matrix without using specgram tool. Is it possible?