In this document are two algorithms showing how to compute the individual twiddle factors of an N-point decimation-in-frequency (DIF) and an N-point decimation-in-time (DIT) FFT.
A Fixed-Point Introduction by Example
Handling Spectral Inversion in Baseband Processing
Understanding the Phasing Method of Single Sideband Modulation
An Interesting Fourier Transform 1/f Noise
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