Questions tagged [frequency-spectrum]

The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain.

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how to normalize DCT (or FFT) coefficients to compare different signals

I have signals that have a broad range of values. I want to compare them in a meaningful way. Just as an example, two of those signals might be: $$f(t)=100\cos(50t)+40\cos(60t) \quad g(t)=2\cos(50t)+0....
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Bandpass filter equivalent for amplitude

I have a signal where I am using a bandpass filter to limit the frequency range. I am also interested in filtering the remaining frequencies (after bandpass filtering) within the signal by their ...
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117 views

One-sided waveforms in both time and frequency?

Can a complex signal be one-sided (causal in time and positive only spectrum in frequency) in both domains? I understand that a function can't have finite support in both domains, but what if both ...
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Belt tension measurement (36 Hz): What should my FFT size be?

These are my setting that I can adjust and I need to measure 36 Hz. +- 1 Hz. What settings do you recommend?
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29 views

fft result with the number of integer multiples of fs

With the cosine signal fc=3Hz and the fs=13Hz as below, fc=3; fs=13; Ts=1/fs; N=101*13; % 101 times of fs n=0:N-1; x=cos(2*pi*fc*n*Ts); and then fft with the ...
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24 views

Finding transfer function from bode plot

Given a bode diagram From the figure, I see that when $\omega = 100 \text{ rad/s}$ the magnitude response starting to go down and when $\omega = 1000 \text{ rad/s}$ the slope become higher. Then $$H(...
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64 views

Transfer of the signal spectrum to zero frequency

There is a signal at a frequency of 6 kHz-6.5 kHz. Sample rate 40kHz. It is required to transfer it to zero frequency. I counted two arrays cos and sin: ...
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Spectrum in real life with Spectrum in theory

as you know it is possible to measure the power spectral density ($|X(f)|^2$) of a certain voltage signal $x(t)$ through a Spectrum Analyzer. As far as I'm concerned, the simplest spectrum analyzer ...
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Meaning of Rect and Train of Rect Spectra

The Fourier transform of $x(t)=\operatorname{rect}(t)$ is $X(f)=\operatorname{sinc}(f)$ The Fourier transform of a periodic train of rectangular pulses $x(t)=\sum\limits_{n=-\infty}^{\infty}\...
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Trying to do frequency analysis of an accelerometer output

I am new to signal processing. I have a 3 axis MEMS accelerometer. I have read its output into $\mbox{Matlab}^{\tt TM}$. My problem is that the signal I am trying to isolate has a frequency of about 0....
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Can we generate signals in reality that have non symmetric magnitude spectrum in the Fourier domain?

I am reading communication systems, and have a doubt: Is it possible to generate signals in reality that have a non-symmetric magnitude spectrum in the Fourier domain? For example, if I have a signal $...
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Fast Sine Wave Recognition

I have a Sine wave at frequency F1. This signal changes and shifts to frequency F2. In frequency domain I like to find this shift as quickly as possible. (Signal has a lot of random noise and hard to ...
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FFT Frequency-Spectrum has noise

I am plotting a Frequency-Amplitude Graph using openGL for the graph and Rosetta FFT implementation for the FFT calculations, I generated a 2 waveform, applied Hanning window, applied FFT and ...
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1answer
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Aliasing in Doppler Radar

my book about RADAR says that: If a Continuous wave radar sends a sine wave at frequency $f_T$ to a moving object (at speed V), a frequency $f_R$ is received. Their difference is called Doppler ...
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The FFT of a sine wave with varying frequency and constant amplitude does not show a plateau, why?

I want to use python to see what the audio response of a speaker is. This would be done by comparing the output of the speaker measured with a microphone to the given input. That means that for both ...
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Why would a time shifted signal have a higher maximum frequency than an unshifted one?

I´m reading the book Numerical Simulation of Optical Wave Propagation by Jason Schmidt. In section 2.1-2.2, the author performs the FFT of a centered and a shifted Gaussian pulse and makes the ...
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Meaning of frequency and bandwidth of a signal, despite the fact that we do not know the signal

First of all, I am completely new to the domain of signal processing. As far as I know, a signal can be represented with an infinite integral of infinitesimal complex exponentials, which is known as a ...
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Does the duration of a signal affect its frequency component's amplitude? Also, does the sampling frequency affect the power of a signal?

I have two questions that are bugging me: Does the duration of an audio signal affect the amplitude of frequency components of that same signal? For example, I am recording the sound of a fan using a ...
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1answer
24 views

Performing root-music, how do i retrieve frequency and phase data of a signal?

I'm trying an alternative method to the classical fft to do signal analysis. I perform root-MUSIC on a certain known signal + noise in matlab with the function 'rootmusic'. This gives gives the signal ...
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1answer
54 views

Brute forcing an aperiodic s-shaped signal to be periodic by mirroring it before performing FFT

I have an aperiodic signal of an s-shape in the time-domain that I would like to filter and calculate the derivative of using the FFT. The jump at the end of the s-shape has, of course, a strong ...
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27 views

Periodogram/PSD from FFT amplitude

I have performed a STFT for signals and obtained the amplitude through ...
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592 views

A DFT “periodic inputs” question

Why do people say that the fast Fourier transform (FFT) “views”, or “interprets”, or “assumes” its input sequence is periodic? I ask this question because the activities of viewing, interpreting, and ...
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30 views

How to interpret a spectrum with FFT mirroring?

I have this code which interprets a few data points on magnetic field strength into a spectrum, as shown below: ...
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156 views

Extremes of integral of the autocorrelation theorem

I am trying to apply the correlation theorem (here attached) to this definition of correlation of a finite continuous signal $g(t)$: $\rho(\tau)=\frac{1}{T} \int_{t_{0}}^{ t_{0}+T}g(t)^{.}g(t+\tau)dt ...
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Apply window taper for selected window or to full data block in algebraic problem with known frequencies?

First, I'd like to introduce a problem. I try to solve a set of linear equations in LS (Least Squares) sense, i.e. Ax=y (LS) => A^TA x = A^T y. x is a vector I'm looking for, but y is a measured ...
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33 views

Isolate g(t) starting from $\int_{-\infty}^{+\infty}g^{2}(t)e^{-i2\pi f t}dt$

Is it possible to isolate $g(t)$ starting from $G^2(f)=\int_{-\infty}^{+\infty}g^{2}(t)e^{-i2\pi f t}dt$ ? Can you show me how?
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Frequency content Signal processing of very large files

I recently had to process a very large file to obtain the power spectrum. The file had about 60m measurements (arguably its not that huge, but its getting to that point). Although, in the end (...
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1answer
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How to get velocity from PSD graph

Hello everyone! I have a graph, which is Spectra inside cavity. PSD vs. frequency. I need to get velocity [m/s] from PSD [dB/Hz]. Does anyone know how to do that?
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81 views

Windowing of signal before FFT

I am facing an interesting problem: I have a signal in the time domain. In order to avoid discontinuities at the edges of the signal --- which would lead to artifacts when calculating the FFT --- I ...
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1answer
199 views

Can I simplify $x=\frac{\ln(|\mathcal F((\mathcal F^{-1}(\sqrt{(f^{-5/3})}))^{2})|)}{\ln(f)}$

Given a variable in time $u_{k}$, and an other variable f which represents the frequencies in a range [a,b]: $$|\mathcal F \left \lbrace u_{k}\right \rbrace |^{2}=f^{-5/3}\tag{1}$$ where $\mathcal F$ ...
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This is how my professor is finding the frequency response of an LTI system when given the impulse response. Is this wrong?

My DSP professor uses the freqz() function to find and plot the frequency response and I think it's wrong but I want to make sure before I point it out. Take this ...
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How to shift frequency bins in audio pitch shifter

I would like to ask you for help to understand shifting frequency bins in audio pitch shifter. I have two issues that I can’t undersrand: FIRST QUESTION At first how to shift frequency bins when ...
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Measurement of frequency deviation in FM signals

Is there any way to measure frequency deviation in a recorded frequency modulated time domain data? The little research i have done on net mostly concerns with frequency deviation measurement using ...
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41 views

Integration of FTIR Absorbance Spectrum in Python

Hello I have a FTIR (fourier transform infrared) absorbance spectrum of a sample, Integrating the single lines is correlated to the quantity of substance present in the sample. The spectrum part I'm ...
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1answer
44 views

power spectrum of passband of ofdm is it right shape or not?

I tried to get power spectrum of ofdm passband signal. Below is the whole matlab code for that with BPSK+ofdm. and I got the power spectrum as below. I wonder that is that right form or not? ...
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How to Quantify a Difference in Spectral Information of two Signals?

As the title states, I am looking for established methods to quantify the difference in two FFTs. I have come across methods such as using cross correlation in the time domain or the coherence ...
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102 views

Welch Method FFT Python - Scaling factor?

I've been implementing a Welch method FFT and I am trying to work out the correct scaling factor that should be applied to the output of the function so the PSD is accurate because at the moment it's ...
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Analysing DAC Spectra: Transient Noise Analysis

I am working with a new Digital-to-Analog Converter (DAC) design in simulation and I'm trying to analyse the output. The device takes in an ideal 14-bit digital representation of a sine wave and ...
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7answers
156 views

Where do harmonics come from?

At first, I thought harmonics come from the signal being periodic. However, we know a sine wave is also periodic but contains a single frequency and no harmonics. A harmonic for me is a component (...
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396 views

Meaning of a null coefficient at 0 Hz

I am analysing a wave with a timespan $\tau$ and after applying the fft I obtain the following plot of the coefficients I assume that the peak at $t=1$ followed by smaller coefficients means that the ...
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How is sampling rate affect the Doppler spectrum? Textbook attached

I am studying FWGN model, in the textbook "MIMO-OFDM wireless communication with MATLAB", it says "When oversampled by a factor of $N_OS$, the bandwidth of Doppler spectrum becomes \...
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1answer
49 views

Spectral peak location estimation using complex DFT

In this paper a simple method to estimate a spectral peak is proposed, by using quadratic interpolation between three samples of the DFT of the signal. Namely, the position of the peak relative to the ...
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1answer
44 views

How does Music algorithm differ from simple DFT/FFT for frequency estimation?

I would like to know why would someone choose to use Music algorithm from frequency estimation when one can simply use DFT/FFT which are much simpler. What is the intuitive way for understanding Music ...
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56 views

Why do I see a frequency shift of the peak between the S11 and impedance response?

I have a resonator I am trying to characterize, and the S11-Plot gives me a slightly different center (resonant) frequency than that of the Z-Plot. These measurements were taken simultaneously and ...
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1answer
35 views

Why do I see a frequency shift from center when transmitting a QPSK via USRP with GNU Radio?

I am transmitting a QPSK signal via GRC and when I look at it on the spectrum analyzer, the signal is shifted away from my center frequency. This shift increases the higher the center frequency (i.e. ...
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Difference in signal Spectrum

[ Here are two figures from the same signal, the 2nd one(B) is after digital predistortion at transmitter end. How can you describe it? What are the improvements and advantages of this technique? Much ...
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Power Spectral Density vs Frequency Domain separation

I am just starting to learn about Power Spectral Density (PSD). What I'm reading is that it is possible to separate PSD masks if they are isolated, even if the frequencies do overlap. My understanding ...
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42 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 ...
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1answer
54 views

What is the significance of the linear phase in the phase response of an M-point moving average filter?

I have plotted the magnitude and the phase responses of an M-point moving average filter, the following are the plots when M = 10: We can observe that corresponding to every lobe in the magnitude ...
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69 views

Why Does ASK Modulation Create Fourier Sidebands?

I know why analog amplitude modulation has side bands, it is related to (fc+fd) and (fc-fd). But what about DAM? ASK(DAM) is a type of digital modulation, and there are only two state: carrier signal ...

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