On 09/01/2015 11:14 AM, Oscar Benjamin wrote:
Just use the next power of 2. Pure powers of 2 are the most efficient for FFT algorithms so it potentially works out better than finding a smaller but similarly composite size to pad to. Finding the next power of 2 is easy to code and never a bad choice.
It would be better to pad to a power of three or five, or some other product of small primes, if the pad length would be significantly less than padding to a power of two. The obvious problem with padding is that it's different from the real data, so its presence will affect the result. At the least, it would be good to pad with the mean value of the original data, or to pad with zero after subtracting the mean from the original data. Phil