When do I normalize by the size of the FFT?
As a result of this symmetry, half of the output Y is redundant (being the complex conjugate of the other half), and so the 1d r2c transforms only output elements 0…n/2 of Y (n/2+1 complex numbers), where the division by 2 is rounded down. When I normalize do I normalize by the size of the fft or the resulting fft_size / 2
Why do we use overlapping frames in FFT?
The basic idea here is that we can average FFT results form overlapping frames and thus obtain a better frequency representation of our time-domain signal. The actual frequency resolution is still the same as without overlapping. As an example, let’s say we use 1024 samples for the FFT and we have a 50% overlap (512 samples).
How does the number of FFTs affect the plot?
In a 2D spectrograph plot, a greater number of FFTs (or STFTs) per unit time will either roughly double the width of the plot, or shrink the X axis dimensioning, when plotting an equal duration.
How does the windowing function affect FFT results?
Most windowing functions (e.g Blackman, Hamming etc) are taper-shaped, which means that they drop to 0 (or close to 0) near the frame edges. This, of course, affects FFT results and we may lose some important information (e.g. transients).
How to create a complex DFT in FFTW?
This function creates the plan: fftw_plan fftw_plan_dft_1d(int n, fftw_complex *in, fftw_complex *out, int sign, unsigned flags); The first argument, n, is the size of the transform you are trying to compute.
Is the argument for FFTW the same as for R2C transforms?
The arguments are the same as for the r2c transforms, except that the input and output data formats are reversed. FFTW computes an unnormalized transform: computing an r2c followed by a c2r transform (or vice versa) will result in the original data multiplied by the size of the transform (the product of the logical dimensions).
What is the logical size of a DFT in R2C?
Instead, r2c DFTs are always FFTW_FORWARDand c2r DFTs are always FFTW_BACKWARD. (For single/long-double precision fftwfand fftwl, doubleshould be replaced by floatand long double, respectively.) Here, nis the “logical” size of the DFT, not necessarily the physical size of the array.