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Search found 98 results on 4 pages for 'fft'.

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• Do you know a good and efficient FFT?

  - by yan bellavance

  Hi, I am trying to find a very fast and efficient Fourier transform (FFT). Does anyone know of any good ones. I need to run it on the iPhone so it must not be intensive. Instead, maybe you know of one that is wavelet like, i need frequency resolution but only a narrow band (vocal audio range up to 10khz max...even 10Khz might be too high). Im…

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• FFT and IFFT on 3D matrix (Matlab)

  - by SteffenDM

  I have a movie with 70 grayscale frames in MATLAB. I have put them in a 3-D matrix, so the dimensions are X, Y and time. I want to determine the frequencies in the time dimension, so I have to calculate the FFT for every point in the 3rd dimension. This is not a problem but I have to return the images to the original form with ifft. In a normal…

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• Getting Frequency Components with FFT

  - by ruhig brauner

  so I was able to solv my last problem but i stubmled upon the next already. So I want to make a simple spectrogram but in oder to do so I want to understand how FFT-libaries work and what they actually calculate and return. (FFT and Signal Processing is the number 1 topic I will get into as soon as I have time but right now, I only have time…

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• Can FFT length affect filtering accuracy?

  - by Charles

  Hi, I am designing a fractional delay filter, and my lagrange coefficient of order 5 h(n) have 6 taps in time domain. I have tested to convolute the h(n) with x(n) which is 5000 sampled signal using matlab, and the result seems ok. When I tried to use FFT and IFFT method, the output is totally wrong. Actually my FFT is computed with 8192 data…

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• fft understanding

  - by maximus

  Can somebody give a good explanation of FFT image transform How the FFT transformed image and it's Re^2+Im^2 image can be analyzed? I just want to understand something when loiking to the image and it's frequency.

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• Help me understand FFT function (Matlab)

  - by estourodepilha.com

  1) Besides the negative frequencies, which is the minimum frequency provided by the FFT function? Is it zero? 2) If it is zero how do we plot zero on a logarithmic scale? 3) The result is always symmetrical? Or it just appears to be symmetrical? 4) If I use abs(fft(y)) to compare 2 signals, may I lose some accuracy?

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• DSP - Filtering in the frequency domain via FFT

  - by Trap

  I've been playing around a little with the Exocortex implementation of the FFT, but I'm having some problems. Whenever I modify the amplitudes of the frequency bins before calling the iFFT the resulting signal contains some clicks and pops, especially when low frequencies are present in the signal (like drums or basses). However, this does…

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• Extrapolation using fft in octave

  - by CFP

  Using GNU octave, I'm computing a fft over a piece of signal, then eliminating some frequencies, and finally reconstructing the signal. This give me a nice approximation of the signal ; but it doesn't give me a way to extrapolate the data. Suppose basically that I have plotted three periods and a half of f: x -> sin(x) + 0.5*sin(3*x) +…

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• Normalize FFT magnitude to imitate WMP

  - by Bevin

  So, I've been working on a little visualizer for sound files, just for fun. I basically wanted to imitate the "Scope" and "Ocean Mist" visualizers in Windows Media Player. Scope was easy enough, but I'm having problems with Ocean Mist. I'm pretty sure that it is some kind of frequency spectrum, but when I do an FFT on my waveform data, I'm…

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• Pitch detection using FFT for trumpet.....

  - by airuslee

  Hi...How do i get frequency using FFT? What's the right procedure and codes?

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• FFT in MATLAB: wrong 0Hz frequency

  - by roujhan

  Hello I want to use fft in MATLAB to analize some exprimental data saved as an excell file. my code: A=xlsread('Book.xls'); G=A'; x=G(2, : ); N=length(x); F=[-N/2:N/2-1]/N; X = abs(fft(x-mean(x),N)) X = fftshift(X); plot(F,X) But it plots a graph with a large 0Hz wrong component, my true frequency is about 395Hz and it is not shown in…

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• VST plugin : using FFT on audio input buffer with arbitrary size, how ?

  - by Led

  I'm getting interested in programming a VST plugin, and I have a basic knowledge of audio dsp's and FFT's. I'd like to use VST.Net, and I'm wondering how to implement an FFT-based effect. The process-code looks like public override void Process(VstAudioBuffer[] inChannels, VstAudioBuffer[] outChannels) If I'm correct, normally the FFT…

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• fft and array-to-image / image-to-array-conversion

  - by kame

  Hello! I want to make a fourier-transformation of an image. But how can I change the picture to an array? And after this I think I should use numpy.fft.rfft2 for the transformation. And how to change back from the array to the image? Thanks in advance.

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• fft algorithm implementation with hadoop

  - by haluk

  Hi, I want to implement Fast Fourier Transform algorithm with Hadoop. I know recursive-fft algorithm but I need your guideline in order to implement it Map/Reduce approach. Any suggestions? Thanks.

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• Calculate area under FFT graph in Matlab

  - by lytheone

  Hiya, Currently I did a FFT of a set of data which gives me a plot with frequency at x axis and amplitude at y axis. I would like to calculate out the area under graph to give me energy. I am not sure how to determinate the area because i am without the equation and also i only want a certain area of the plot rather than whole area…

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• Difference in amplitude from the same source using FFT

  - by Anders

  Hi, I have a question regarding use of FFT. Using function getBand(int i) with Minim i can extract the amplitude of a specific frequency and do pretty maps of it. Works great. However, this is a more of a curiosity question. When i look at the values extracted from playing the same song two twice using the same frequency (so the…

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• Matlab fft function

  - by CTZStef

  The code below is from the Matlab 2011a help about fft function. I think there is a problem here : why do they multiply t(1:50) by Fs, and then say it's time in millisecond ? Certainly, it happens to be true in this very particular case, but change the value of Fs to, say, 2000, and it won't work anymore, obviously because of this…

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• c++ FFT Beat detection library?

  - by mokaschitta

  Hi, I am currently looking around for a good allround beat detection library / source code in C++ since I found it really hard to achieve satisfying results with the beat detection code I wrote myself using this tutorial: http://www.gamedev.net/reference/programming/features/beatdetection/ It's especially really hard if you want…

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• AS3 computeSpectrum fft true

  - by cr1ms0n3cho

  I am just trying to understand what the values sent back from computeSpectrum(bytes,true,0) mean. I have values ranging from 0 to 1 for each float i read from the byte array but does each value represent a range of Hz Thanks!

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• How to compute power spectrum from 2D FFT

  - by user1452954

  I've encounter a problem when doing my lab assignment, not sure how to implement this: Use fft2 on a gray image and to do Fourier transform and then compute the power spectrum. This is my code so far: >> Pc = imread('pckint.jpg'); >> whos Pc; Name Size Bytes Class Attributes Pc …

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• VB FFT - stuck understanding relationship of results to frequency

  - by WaveyDavey

  Trying to understand an fft (Fast Fourier Transform) routine I'm using (stealing)(recycling) Input is an array of 512 data points which are a sample waveform. Test data is generated into this array. fft transforms this array into frequency domain. Trying to understand relationship between freq, period, sample rate and…

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• Beat detection and FFT

  - by Quincy

  So I am working on a platformer game which includes music with beat detection. I am currently using a simple if the energy that is stored in the history buffer is smaller then the current energy there is a beat. The problem with this is that ofcourse if you use songs like rock songs where you have a pretty steady…

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• Logarithmic spacing of FFT bins

  - by Mykel Stone

  I'm trying to do the examples within the GameDev.net Beat Detection article ( http://archive.gamedev.net/archive/reference/programming/features/beatdetection/index.html ) I have no issue with performing a FFT and getting the frequency data and doing most of the article. I'm running into trouble though in the…

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• Logarithmic spacing of FFT subbands

  - by Mykel Stone

  I'm trying to do the examples within the GameDev.net Beat Detection article ( http://archive.gamedev.net/archive/reference/programming/features/beatdetection/index.html ) I have no issue with performing a FFT and getting the frequency data and doing most of the article. I'm running into trouble though in the…

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• Why do I get rows of zeros in my 2D fft?

  - by Nicholas Pringle

  I am trying to replicate the results from a paper. "Two-dimensional Fourier Transform (2D-FT) in space and time along sections of constant latitude (east-west) and longitude (north-south) were used to characterize the spectrum of the simulated flux variability south of 40degS." - Lenton et al(2006) The…

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