When sending audio files over the internet is requested. You could just send the whole song the way the record company recorded it, but the file is too big when it's that way. The reason for its size is that it is a complete, lossless recording: every frequency is preserved from recording, through the entire mix, to the final track. Applying the Fourier transform to a small portion of a song, however, there are some frequency components that are dominant and others that barely appear.
