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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Why does my digital upconversion result in two tones?

I am using Xilinx's RFSoC in I/Q mode. The important point is that in the digital space I have real and complex samples. I take the incoming data and multiply it by a complex sinusoid. In my test ...
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Confusing regarding triangular wave vs square wave?

I am reading signal processing first by Mcclellan. In chapter 3, I came across the term "discontinous" as shown underlined in attached photo. Apparently "discontinuous" means having a gap/break but ...
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Confused in Smoothing a signal in the Frequency domain

First of all i am new in DSP, so i have no solid education in the field. I have convert my time domain acceleration-seismic data to frequency using DFT and i am trying to smooth the DFT data, in ...
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64 views

What is issue in square wave reconstruction?

As shown in attached photo: What is the reason that the approximate square wave $$x_N (t)$$ at right side is not like the original $$x(t)$$ at left side .? Is the only reason is that number of ...
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Is it true that each and every signal has multiple frequency components?

Usually when we observe spectrum of a signal,we see multiple frequency components, each having different contribution to amplitude But is it true that each and every signal has multiple frequency ...
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Visualizing the “frequency shift” theorem in FFT

I was trying to visualize the frequency shift theorem in MATLAB, which states that if the Fourier transform G(f) is shifted by a constant $f_o$, its inverse transform g(t) is multiplied by $e^{j2\pi ...
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3answers
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Complex exp. Fourier series, finding $x(t)$ when $X(j\omega)$ is given as magnitude and phase plot

I'm watching Neso Academy series on Signals and Systems, and in one of the videos the problem is to find $x(t)$ when magnitude and phase plot are given. The plot looks like this: When he finishes ...
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Does negative frequency actually exist or it is just theoretical?

This below questions gives good explanation regarding negative frequency What is the physical significance of negative frequencies? But I have one query Does negative frequency only exist ...
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1answer
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Different amplitude in time-domain vs frequency-domain

Reading the book Understanding Digital Signal Processing I am confused with the following picture: First figure is the input signal ($x_1(n) = \sin(2\pi f_0nt_s)$, $f_0$ frequency, $t_s$ being the ...
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1answer
37 views

What is the formula for the frequency spectrum?

A signal $f[n]$ is given, the corresponding DTFT as $F(e^{j\omega})$ and a plot of the frequency spectrum $f(t)$. Unfortunately I can't find a formula for the frequency spectrum in my documents. When ...
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Using the log power spectrum as features for a Classifier

I have a set of time series signals for which I have to develop a anomaly detection algorithm. I am considering using classifiers like SVM to do this. However I am confused about how to properly ...
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Strange FFT spectrum after resampling

I'm pretty new to signal processing and have encountered strange behaviour. I have a vibration signal from a non-stationary gearbox component that I need to resample to do order analysis. The ...
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Proof that spectrum analyzer measures mathematical Power Spectral Density

It seems to me the power spectral density (PSD) is defined as follows. Consider a signal $X(t)$ The windowed version of this signal is Consider a signal $X(t)$. We defined a time-windowed version of $...
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Frequency change detection in step-wise frequency chirp

I am driving a system with a step-wise frequency chirp from 50-400 hz with a frequency step of 0.01 hz. I am having difficulty identifying the points of frequency change as the data collected has an ...
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Meaning of spectrum in simple words?

What is the meaning of spectrum in simple words? Is it just "range or set of different frequencies " Just like fm spectrum is between 88MHZ to 108MHZ?
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How to generate a sinusoid with STFT at a frequency which is between bins

Is it possible to generate a sinusoid at a frequency which is between two bins (so a fractional index) with the STFT algorithm (by filling bins and doing the inverse) ? If yes then how can this be ...
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What is the relation between PCM amplitude values and the values in a Spectrogram?

I am curious to know the relation between the 16-bit amplitude values in the PCM-encoded signal and the values inside the corresponding spectrogram. I am using Scipy reading a 44100-sample rate song: ...
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47 views

Power Spectrum and Power Spectral Density

From signal theory we know that a very useful representation of some power signals is that of its power spectral density, whose curve represents how the total power of the signal is distributed at all ...
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1answer
55 views

How can I improve the resolution of a spectrogram of a low-frequency signal with high sampling frequency (Python)?

Imagine you have signals $x_1(t)$ and $x_2(t)$ that contain a limited number of periods of low frequency oscillations and are sampled at 44100Hz (coming from an external source) and you want to obtain ...
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1answer
34 views

Correct signal analysis flow (Wind Turbine vibration)?

I have vibration data from WT (gearbox) sampled at 25.6 kHz. From a previous post I received a lot of good recommendation. What I am trying to do: Find early stage bearing faults by using an ...
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How to estimate the frequency of a feature in an image?

I have a background in the 1-D signal analysis but I am totally new to image analysis. I would appreciate any help. Given the following original image and the downsampled image, as you could see, ...
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Are higher frequency components of constant amplitude of a square wave dependent only on the rise time and independent of square wave frequency?

This question based on the observation that ringing on square wave due to multiple reflections on a transmission line doesn't change with the change in frequency of square wave. From this observation ...
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Envelope analyis basic question

I have a vibration signal sampled at 25.6 kHz, and I want to perform Envelope Analysis on it. "Vibration-Based Condition Monitoring of Wind Turbines" by T. Barszcz has the following figure: I ...
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2answers
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Wind Turbine Vibration Analysis: Which approach?

I'm analysing vibration data from 4 wind turbines (WTs). 8 different sensors are sampled at 25.6 kHz for 10 seconds once a day. I have data from around 400 days (intervals). The plot underneath is for ...
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Relation between Gaussian and bi-Gaussian distribution

A Gaussian Doppler Spectrum can be seen as a bi-Gaussian Doppler spectrum in wich only one Gaussian function is present ( the second having a zero power gain) ? any help will be really appreciated
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How to compute position by FFT?

I have FFT data of x, y, z - axis, Now I'm trying to find the position through FFT data. Step 1 : For that, applied corresponds to an ordinary frequency i.e rad·s−1, ...
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1answer
44 views

Jamming resistance in spread spectrum systems

In direct sequence spread spectrum, which is the basis of CDMA systems, the baseband signal is multiplied with a pseudo noise (PN) sequence which has a high chip rate, thus the resulting modulated ...
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1answer
63 views

How to make low pass filter using frequency sampling method?

https://www.allaboutcircuits.com/technical-articles/design-of-fir-filters-using-frequency-sampling-method/ So there is two main equation: I wish to filter out frequency $\le 10000Hz$, for example. ...
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Vibration analysis: harmonics' amplitude

I am studying the vibrations on a FZG gear test rig with two accelerometers on the casing of the gears. These accelerometers sample at a rate of 10kHz. When looking at the main amplitude peaks on the ...
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2answers
66 views

Why am I not getting a flat phase for a Gaussian pulse when doing a Fourier transform in Python?

I have been trying to obtain a spectrum and a spectral phase of a Gaussian pulse using the Fast Fourier Transform provided with numpy library in Python. Here are ...
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62 views

Phase shifting in frequency domain

I am aware this topic has already been addressed in at least one question here, but despite that I could not find the solution to my problem. Also bear patience with me since I am not a mathematics ...
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1answer
37 views

How to create a wide-sense stationary time series with a frequency of 40 Hz?

I want to create a time series in MATLAB which has a peak frequency of 40 Hz but is also a wide-sense stationary random process. I then want to use power spectral density estimation to recover the ...
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Fast Fourier Transform for varying period (Order analysis)

I am trying to do a fast Fourier transformation on accelerometer data from a shaft rotating at varying speed in Python. What I have done so far: 1: The original plot was in the time domain, and I ...
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1answer
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Phase response distortion due to IQ demodulation

I have a bandpass signal, I do IQ demodulation meaning: first step: $IQ(t) = x(t)*exp(-2\pi f_ct)$ second step: low pass using $filtfilt$ function in MATLAB. (in order to avoid phase ...
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1answer
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Aliasing and DTFT of a real signal

We are analyzing a real signal with the DTFT. Since we are using a limited number of samples it's like we are transforming a finite signal. As I remember, the FT of a finite signal has an infinite ...
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1answer
54 views

Negative frequency of a sinusoidal wave on the magnitude spectrum: Physical explanation?

link to the video: Negative frequency Must a cosine function be expressed as two exp functions with opposite frequencies/directions of rotation and half the magnitude/amplitude(1/2), therefore ...
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Obtain SIB1 messages from CPRI the captured DL IQ data

I am a beginner in the signal processing, and I know some python and I have a project I'm working on which is about Obtaining SIB1 messages from CPRI the captured DL IQ data. I have captured some DL ...
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1answer
124 views

Scaling a wavelet in continuous wavelet transform

The mexican hat wavelet, obtained from the second derivative of a Gaussian, has a functional form of $$ \frac{2}{\sqrt{3 \sqrt{\pi} \sigma \ }} \left(1-\frac{t^2}{\sigma^2} \right) e^{-t^2/(2\sigma^...
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1answer
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Shazam / SoundHound Music Analysis - Recommendation for Reading

I need to explore some area around music frequency analysis. A good example is the way Shazam / SoundHound app works (mapping frequency domain, comparing, creating some vector map, handling noises and ...
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2answers
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Why is the carrier suppressed by AM-DSB-SC modulation?

Lets say I have a message that is a sine wave at 1KHz. As I understand it, I can perform amplitude modulation by multiplying this signal with a carrier, lets say 10KHz, and this process is essentially ...
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1answer
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GPS Receiver in Frequency Domain

I'm trying to transmit and receiver the GPS payload in both Time and Frequency Domain. For transmitting and receiving in time domain : ...
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1answer
54 views

Difference between “scaled white noise ” vs. “unscaled white noise”

I have been searching Matlab user-guide for Wavelets. In their graphical user interface for denoising, there is an option for "unscaled white noise" and "scaled white noise" for the noise structure. ...
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(Frequency Offset): Relationship between Normalized Carrier Frequency Offset (normalized CFO) & ppm in OFDM system

How can I change a normalized carrier frequency offset (CFO) to ppm? And If the DAC sampling rate is 30GS/s, and the clock frequency is 15GHz, then should I use 30G or 15G when I calculate ppm? ...
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How modulate and shift in frequency?

I have a 16-QAM constellation, then I divide it into imaginary part and real part. I convolve both by Srrc pulse and multiply by cos(2*pifct) and -sen(2*pifct). Let's say fc equal to 40 MHz Now, we ...
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1answer
50 views

Spectrogram of an executable binary [closed]

One of the approaches I have been searching so far is the application of utilizing Neural Network to classify Spectrogram images, which is heavily used in speech recognition. I am conducting an ...
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Where can I find more information about how to create filters on frequency domain?

I'm newbie and I'm very interested in filtering images on frequency domain. I haven't found a lot filters on frequency domain and I wondering how can I create new ones. How can I create new ones? ...
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Remove brighter regions in an image on frequency domain

I'm newbie and maybe this is not the right place to ask this question, or this question has no sense. I'm very interested in working on filtering images on frequency domain. I have found a few ...
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1answer
31 views

How do I apply the Nyquist criterion on the following spectrum to see if it satisfies the criterion or not?

I am trying to find out if the pulse in the figure satisfies the Nyquist criterion for a modulation interval T. I'm used to the Nyqusit frequency, but I cannot grasp what the Nyquist criterion is ...
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