In reality, you can't. Since the fourier transform was designed for a continuous signal, it needs some modifications to tailor it to work in a digital world whe

In reality, you can't. Since the fourier transform was designed for a continuous signal, it needs some modifications to tailor it to work in a digital world where, instead of a continuous signal, you periodically sample the waveform at regular intervals and use the discrete fourier transform (DFT) or its more efficient little brother, the fast fourier transform (FFT). Both these work off N samples of the waveform at a time.