Questions tagged [fourier]

Anything related to Fourier series, Fourier transform and similar mathematical tools used to analyze the frequency content of a signal.

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How to use Fourier analysis for a daily sound? [closed]

Consider I want to set up a device to record any sound near my resident. It will be, of course, record all sounds, including humans sound, birds, cats, dogs, cars, motors, building constructions, wind ...
AirCraft Lover's user avatar
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Fourier series complex to real

I have to find the Fourier series of this function in complex form and transfer it to real: \$f:(-\pi;\pi]\to \mathbb{R},\;\;\;f(x)= \begin{cases} x & -\frac{\pi}{2} \leq x \leq \frac{\pi}{2} \\ 0 ...
hello447's user avatar
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Z transform and the magnitude of Fourier transform

Would like to know if the graph of the magnitude in the picture I added is correct. Should I address the other pole?
Adi Goyte's user avatar
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3 answers
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Fourier circuit analysis of a RLC circuit

I was trying to calculate output voltage across the inductor in the RLC circuit below. I had used the Fourier transform to convert input signal \$V_{i}(t)\$ which is a single rectangular wave pulse in ...
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FFT of a real sequence

I know there are many questions (almost the same as this one) on this forum and I am sure I have read most of them, however, I still cannot answer this question: I use the RFFT function of ARM CMSIS (...
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FFT basic concepts

This is my first time studying the Fourier transform. I can't understand some basic and somewhat more "practical" concepts from the formulas . EXAMPLE: I have a 1kHz sinewave with 1ms period....
KaleM's user avatar
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Discrete Fourier transform for musical analysis

I am a senior in highschool and am currently trying to conduct an exploration on Fourier analysis, specifically using the discrete Fourier transform to analyze a chord played on my piano. Basically I'...
Ralph Khouri's user avatar
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Equation for a Triangle wave shape [closed]

So I have this function, and is it writter analytically. I cannot understand how do we get 4Um/T and 2UM- 4Um/T or -4Um + 4Um/T. What I mean is that I have tried formula like this when I take u(t) ...
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Can an entire signal with transients be reconstructed from an inverse Fourier transform?

If we have a long signal (say some music) that contains a lot of transients at different frequencies (i.e. the relative "volume" of each different frequency changes over time) and we take a ...
thepman's user avatar
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Why does MATLAB show a pole in bode plot of an underdamped second order system at natural frequency?

I am using the sisotool in MATLAB to obtain the bode plot of the following transfer function: MATLAB marks a pole at wo which is approximately 11.18 What is the meaning of this? How would you even ...
needbrainscratched's user avatar
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Sketching fourier transform after sampling

I'm having trouble understanding how this system is supposed to work. My sketch (all my sketches are for fourier transforms) for \$X_b(jw)\$ are two pyramids centered at 7pi and -7pi with height 1/2. ...
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Why don't we use the third harmonic in power transmission?

For some high power high voltage lines DC is used with the advantage that sinus wave AC obviously doesn't use the line to it's maximum capacity at all times. To correct this, we could use square wave ...
Čäřý's user avatar
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DC bus capacitance design for SPWM inverter

I am working on a 5kW grid-connected inverter where I need to find the DC bus capacitance value. I understand that the capacitor serves 2 purposes: 1) to provide a low impedance path for the high ...
curious_direwolf's user avatar
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Frequency spectrum in PLECS for CM noise measurement

I am performing a simulation to measure the common mode noise in a buck converter. I have three models, an ideal buck, a non-ideal buck with parasitic capacitors, and a CM equivalent circuit to ...
ORion's user avatar
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How to properly take the discrete Fourier transform of a signal as well as calculate the power spectral density of the DFT?

I'm getting conflicting answers on how to properly represent a DFT and normalize the results as well as calculate the normalized PSD of the time series. For background, I typically work with voltage ...
Simeon K's user avatar
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How would you compute Fourier transform of a real world signal where the signal keeps getting updated (not a static one)?

A very naive question: How do we use Fourier transform for real world signals - for which you have the information only up to the present instant (and the present time keeps moving continuously)? The ...
Dynamic_equilibrium's user avatar
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Need help on signals and systems, Fourier representation of a signal

I've got a homework question for my signals and systems class. In the question, we're given the graph of the magnitude and the phase of a continuous signal. Here are the graphs: I have to find the ...
the big's user avatar
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Fourier Transform of Voltage Readings

I am working on developing a Fourier transform for voltage readings. The goal is to determine voltages at different frequencies (frequency domain). I am taking readings at 100Hz and am measuring both ...
GGonzales0603's user avatar
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FFT analysis in LTSpice is giving wrong results during partial execution of time domain simulation (Details in body)

In LTspice, while computing FFT using waveform window (View-> FFT), the results seems to be wrong if FFT is computed after partial execution of simulation ( eg: if simulation is paused in between)...
Dynamic_equilibrium's user avatar
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What is the structure and type of harmonics generated by a very differentiated square wave (i.e bipolar spikes)?

this question is in two parts. Firstly, can you please tell me what the structure and amplitude distribution is of harmonics generated by a differentiated square wave of 50% duty cycle, where the time ...
Jeff's user avatar
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Calculating inverse fourier transform and graphing it

Recently I stumbled upon Fourier transforms which means I am very new to it. I've been given a question from my professor to find the inverse Fourier transform of a frequency spectrum which is given ...
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FSK Modulation in Python

I am currently writing a script that uses I/Q data to do FSK modulation. My question is about the FFT plot. I expected to have a peak at 1Hz and 2Hz which are the frequencies that represent binary 0 ...
PrematureCorn's user avatar
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A DFT-based phasor estimation

I have the sample set of ideal and real secondary current during CT saturation, need to apply the DFT analysis to samples and estimate the fundamental phasor (magnitude and phase angle) of samples (...
sakayevas's user avatar
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Fourier series from the graph

I am trying to find the power spectral density, autocorrelation function, and power content of a periodic signal. In order to do this I need to find the Fourier series coefficients. I am trying to ...
merovingian's user avatar
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Fourier transform plot

A continuous-time signal x with bandwidth \$\frac{20π}{3}\$ rad/sec is sampled with sampling period \$T_s = 0.1\$ seconds to obtain a discrete-time signal \$x_s[n] = x(nT_s)\$ for all n. The discrete-...
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Time period for analysing an instantaneous sound wave and then converting it to the frequency domain?

I am confused about how a signal is analysed in the frequency domain after being recorded in the time domain instantly. Does the spectrum of frequencies that are displayed based on a previous period, ...
user avatar
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Confusions regarding Laplace transform

We know that Laplace transform has two parts, \$\sigma \$ and \$ j\omega\$. \$\sigma\$ is the real part while \$ j\omega\$ is the imaginary part. Is it okay to say that the term \$\sigma \$ is a ...
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Mathematical difference between FFT and STFT

Can a FFT be recreated by performing STFT on the smaller time intervals and then summing them up. My doubt is that FFT is a usually a amplitude vs frequency data and STFT has a x-axis in units of time....
avi0105's user avatar
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Transfer function of two frequency spectra

When you have two amplitude frequency spectra (fourier spectrum), in this case of a torque ripple, how do you define the transfer function (or the ratio) between both? How do you "divide" ...
Livio Luyten's user avatar
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2 answers
417 views

How does this modulation cause sidebands?

The following figure is an excerpt from this paper: Input Differential-Mode EMI of CRM BoostPFC Converter by Fei Yang. Q#1 (first highlighted sentence): How does the modulation line frequency cause ...
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A half-wave rectified sinusoidal waveform has a peak voltage of 10V. What are its average value and the peak value of the fundamental component?

I know to to find average value: 10/pi What does "peak value of fundamental component" mean?
Vedhant Abrol's user avatar
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Signal Dimensions in Simulink

I'm using R2022a, in Simulink I can not find the Display tab to access Signals & Ports>Signal Dimensions. Could someone point me in the right direction please?. Also, in the figure below the ...
Kalamakra's user avatar
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Downconversion Intermodulation Frequencies - Where do they come from?

I recently came across this video which discusses the downconversion of a signal (referred to as IN) to an Intermediate Frequency (IF) using a Local Oscillator (LO). I'm assuming that all of these ...
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Confused about the similarities between Fourier Series and Fourier Transform

My understanding of Fourier Series was, it is a method that decomposes a periodic signal into sum of signal given by infinite number of sines and cosines. And in case of Fourier Transform it was, that ...
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Why does a cosine function have a non-infinite Fourier coefficient?

I took my signals class a long time ago and have gotten used to using Fourier tables for a lot of things. I'm reading a textbook on communications and I stared at the Fourier transform equation for a ...
CEEA's user avatar
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Why is this signal considered odd when v(t) is not equal to -v(-t)?

In the solution of a problem, that asked to find the Fourier Series of the waveform, shown below. The coefficient of cosine part an is taken taken 0, because it is ...
theCursedPirate's user avatar
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3 answers
573 views

Signals and systems - Find the inverse Fourier transform of a RLC circuit

I was analyzing the following RLC circuit: And applying the Fourier transform on the circuit, I ended up with the following transfer function: $$ H(\omega)=\frac{V_c(\omega)}{V_i(\omega)}=\frac{1}{1+...
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Why do we have two separate transforms for transforming a time domain signal to the frequency domain? [duplicate]

I know that Laplace transform and Fourier transform are not exactly equal; they will be equal when alpha = jω. But according to my understanding, both transforms convert a time domain signal to the ...
Talha's user avatar
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Why am I getting linear phase?

I'm trying to plot the phase of Fourier transform of the function below: \begin{gather*} x[n] = 2e^{-0.9|n|} \: \: n \in [-5,5]\\ x[n] = 0 \:\: n \notin [-5,5] \end{gather*} which is equal to the ...
AmirHossein Bagheri's user avatar
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Numpy giving the wrong Fourier transform of sine functions

I'm using numpy's FFT to calculate the Fourier transform of \$\cos(\omega_0t)\$ and plot it. By using the definition we can derive its Fourier transform as below: \begin{equation} X_3(j\omega) = \pi (...
nothatcreative5's user avatar
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1 answer
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Phase of Fourier transform when it arrives at \$ \pi \$

I'm trying to calculate the phase of "rect" which is like below \begin{equation} f(x)=\begin{cases} 1 & \text{if }256<x<768,\\ 0 & \text{otherwise}. \end{cases} \...
AmirHossein Bagheri's user avatar
2 votes
2 answers
204 views

Fourier transform and what it represents

Suppose we have a sine voltage supplied to a resistive load. When I perform a Fourier transform to this signal in the frequency domain what do I get? All values of g(a) will be 0 except for the ...
Cartoon Ryan's user avatar
1 vote
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Frequency domain analysis when sampling a switched (gated) integrator

I would like to use AC analysis (e.g. in spice) on a non-ideal op-amp integrator where the reset switch is open, and then apply a shaping function to the result of the AC simulation (in the frequency ...
HKOB's user avatar
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How to use DFT to find harmonic content of an AC waveform?

I am kind of new to this coding and simulation environment. For my first project I need to take samples of current signals from power line and find out the harmonic contents using DFT. I haven't done ...
Vineeth's user avatar
2 votes
2 answers
601 views

Bandwidth of a signal

I have found that the convolution of two rect(f) functions (f=frequency) gives a triangular pulse of width 2 centred at 0 Hz. Can anyone tell me what the bandwidth of this pulse is? Is it F or 2F? My ...
Jonathan_the_seagull's user avatar
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3 answers
226 views

.FOUR command doesn't give the required output

This netlist for a full wave rectifier was actually written for PSPICE. When I type the same netlist in LTSpiceXVII, the log file doesn't show the proper output. I have replaced ...
p_p's user avatar
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1 answer
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Fourier Series - Double Check Work

I was solving this Fourier series problem from my book, but was not able to find a solution to it to double-check my work. This is the problem: My work: \$T=4+2=6 sec\$ \$C_{n}=(\frac{1}{T})(\int_{t_{...
Damianpd's user avatar
2 votes
5 answers
2k views

Does the DC component of any signal also carry information?

Every signal carries some types of information in it. Mathematically we Know from Fourier series that these signals can be represented as a sum of its DC component and all the harmonics of fundamental ...
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Why is a signal that is finite in time domain, infinite in its frequency domain?

Why does every single band-limited signal in frequency have an infinite time domain and vice versa (As it's a symmetric relation, inf in one is finite in the other). I understand how a digital signal ...
JustLearning321's user avatar
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2 answers
350 views

Inverter Fourier analysis

I have an inverter circuit like below: I will use bipolar control method to produce sine wave. Our teacher said us prove basic harmonic of inverter is equal to multiplying of modulation index and Vd, ...
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