fft

问题 I am working on implementing an algorithm using vDSP. 1) take FFT 2) take log of square of absolute value (can be done with lookup table) 3) take another FFT 4) take absolute value I'm not sure if it is up to me to throw the incoming data through a windowing function before I run the FFT on it. vDSP_fft_zrip(setupReal, &A, stride, log2n, direction); that is my FFT function Do I need to throw the data through vDSP_hamm_window(...) first? 回答1: The iOS Accelerate library function vDSP_fft_zrip()

问题 I want to get the RMS after doing the fft to my data in order to get the same result as the RMS of data directly. I followed this topic https://fr.mathworks.com/matlabcentral/answers/131353-relation-between-fft-and-rms but I can't get the same results, it's a big difference. By Parseval's theorem "The total energy of a signal is preserved under the Fourier transform ( Parseval's theorem ), so the sum (or integral) of the square of a function is equal to the sum (or integral) of the square of

问题 I have a current signal (extracted in csv) which I obtained from cadence simulation over 30ns time. I have removed DC offset and applied windowing function before FFT. And normalized FFT by sqrt(N) . I have shift zero-frequency component to center of my desired spectrum with fftshift(X) . I got my desired FFT. I also want to get back to my original windowed signal by ifft but it is not showing my windowed signal instead it is showing only a version of the window function that I used. My

问题 I have a current signal (extracted in csv) which I obtained from cadence simulation over 30ns time. I have removed DC offset and applied windowing function before FFT. And normalized FFT by sqrt(N) . I have shift zero-frequency component to center of my desired spectrum with fftshift(X) . I got my desired FFT. I also want to get back to my original windowed signal by ifft but it is not showing my windowed signal instead it is showing only a version of the window function that I used. My

问题 I want to plot the frequency spectrum (like they do for example in Audacity). Hence I want the frequency in Hertz on the x-axis and the amplitude on the y-axis. My input is a periodically sine wave with 0,7 as amplitude and 500HZ as frequency.I use FFTW to compute the magnitude and QWT to plot. My problem , what parameters should I put in setSamples to get a pic on 500 HZ ? Any help would be appreciated here is my code 回答1: From documentation you must set two pointers to data that build the

问题 I have a working tone detector which uses an FFT to determine whether a tone (or tone pair) of a particular frequency is present in an audio stream (if sufficiently above the noise floor). What method could I use to more precisely locate the onset time and duration of that tone? I am looking for something far more precise than the FFT frame duration (about 50 ms). The tone is assumed to be much longer than an FFT frame. 回答1: If the particular frequency is known ahead of time, you could design

问题 When I am using jTransform. https://sites.google.com/site/piotrwendykier/software/jtransforms with my app to perform FFT to my pcm data, I got the exception java.lang.NoClassDefFoundError: edu.emory.mathcs.jtransforms.fft.DoubleFFt_1D while I added the jtransform.jar in my app.And also update the build path. 回答1: 1.In Project properties -> Java build path -> Order and export, check all your added dependencies to be included with project class files. 2.Select Android Tools > Fix Project

问题 Here is a mass-spring-damper system with an impulse response, h and an arbitrary forcing function, f ( cos(t) in this case). I am trying to use Matlab's FFT function in order to perform convolution in the frequency domain. I am expecting for the output ( ifft(conv) ) to be the solution to the mass-spring-damper system with the specified forcing, however my plot looks completely wrong! So, i must be implementing something wrong. Please help me find my errors in my code below! Thanks clear

问题 This is a follow-up to an answered question that I asked and that can be found here. I have several points (x,y,z coordinates) in a 3D box with associated masses. I want to draw an histogram of the mass-density that is found in spheres of a given radius R . The idea is to compute a 3D histogram of my box (with binning much smaller than the radius), take its FFT, multiply by the filter (a ball in real space) and inverse FFT the result. From there, I just compute the 1D histogram of the values

问题 I am trying to use the NumPy library for Python to do some frequency analysis. I have two .wav files that both contain a 440 Hz sine wave. One of them I generated with the NumPy sine function, and the other I generated in Audacity. The FFT works on the Python-generated one, but does nothing on the Audacity one. Here are links to the two files: The non-working file: 440_audacity.wav The working file: 440_gen.wav This is the code I am using to do the Fourier transform: import numpy as np import