Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [fft]

The fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse.

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What is a frequency bin?

I'm doing a research on the FFT method, and a term that always comes up is "frequency bin". From what I understand, this has something to do with the band created around the frequency of a given sinusoid, but I can't really figure out how. I also…
JonTrav1
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FFT of sine wave not coming as expected i.e single point

The cyan plot is a spectrum of 50 Hz, and the magenta one is a 50.1 Hz sine wave (having amplitude 0.7). Both are sampled at 1024 samples/s. I performed a 1024 point FFT to get this spectrum. Why is only the 50Hz spectrum a single value? Why does…
gpuguy
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What data should I use to test an FFT implementation, and what accuracy should I expect?

I'm involved with an effort to implement an FFT algorithm, and am curious what the recommended advice is for the input test data to use -- and why! -- and what accuracy to expect. On test inputs, I've found a little guidance in old Usenet posts that…
Brooks Moses
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Intuition for sidelobes in FFT

I was wondering if there's a intuitive way to understand why sidelobes appear when performing an FFT on a signal of fixed length?
CatsLoveJazz
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FFT time domain average vs frequency bin average

I have multiple trials of physiological data. I am doing a frequency based analysis to analyze power (amplitude) in certain frequencies of interest. Is averaging multiple trials of equal length and then taking a single FFT of the averaged signal vs…
user1487551
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Algorithms for computing FFT in parallel

I am trying to parallelize the computation of an FFT on terabyte-sized signal files. Right now such an FFT using an open-source library takes many hours, even running through CUDA on the fastest GPU I have. The framework I am trying to adapt to this…
Philipp
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Radix-4 FFT versus Radix-2

Is a radix-4 implementation faster than a equivalently well coded radix-2 FFT? And if so, why would it be faster?
hotpaw2
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FFT Processing Gain

When transforming a noisy signal via Fast Fourier Transform from time to frequency domain there is a "Processing gain" of the FFT which increases as number of bins increases. I.e. the more bins I have the more the noise floor in the freqeuency…
Frank
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FFT of size not a power of 2

My question is regarding the input size of a signal which is not a power of 2 and we have to take the fft of it. Some solutions say that suppose if we want to take the fft of 1800 we should zero pad it till the length of 2048 to make it power of 2…
D X
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How do window size, sample rate influence FFT pitch estimation?

I am trying to create a pitch-detection program which extracts the frequencies of peaks in a power spectrum obtained from an FFT (fftpack). I am extracting the peak frequencies from my spectrum using Quinn's First Estimator to interpolate between…
willpett
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Is it valid to increase amplitude (and presumably FFT quality) by simply scaling the data?

I'm using a version of "KISS FFT" by Mark Borgerding. It accepts an array of 16-bit fixed-point input values and produces a 32-bit float result array. I've discovered that if the input amplitudes are low many of the float result values come out…
Daniel R Hicks
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Can I use FFT to interpret accelerometer gestures?

I have the need to detect two different gestures that occur when looking at accelerometer data. Here's a run down (as brief as I can make it): Lets say an iPhone is being oscillated back and forth while remaining face-up. The user can either do one…
rykardo
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How can I detect potholes using an accelerometer mounted in a vehicle?

I am currently studying DSP and FFT, I am very new to this and have been doing electronics for a long time with Arduino and hobby projects. Recently, I am doing a project with the goal to map potholes along your daily commute in the car, measuring…
zacharoni16
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Can someone help explain what this FFT workflow is doing to my signal, and why it works?

I am working with a piece of equipment that does acoustic analysis. It does this by acquiring a time domain signal and performing an FFT on it to extract the amplitude and phase at a single desired frequency, call it f0. Now, I understand the FFT.…
Ben S.
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radix-4 FFT implementation

I implemented a 4-point radix-4 FFT and found that I need to do some manipulation of the output terms to get it to match a dft. My code is a pretty direct implementation of the matrix-formulation so I'm not clear on what the problem is // …
moloned
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