The Radix 2 FFT

When $N$ is a power of $2$, say $N=2^K$, then the above DIT decomposition can be performed $K-1$ times, until each DFT is length $2$. A length $2$ DFT requires no multiplies. The overall result is called a radix 2 FFT. A different radix 2 FFT is derived by performing decimation in frequency.

In software, a split radix FFT is usually more efficient than a pure radix 2 algorithm [58]. This typically means terminating the DIT decomposition on a combination of radix 2 and radix 4 FFTs.