Digital Sound & Music: Concepts, Applications, & Science, Chapter 2, last updated 6/25/2013

48

usually gives good results. If you set the size to 2048 and play the piece of music loaded into

Audition, you'll see the frequencies in the frequency analysis view bounce up and down,

reflecting the changing frequencies in the music as time pass.

Figure 2.50 Choice of FFT window size in Adobe Audition

2.3.11 Windowing Functions to Eliminate Spectral

Leakage

In addition to choosing the FFT window size, audio processing programs often let you choose

from a number of windowing functions. The purpose of an FFT windowing function is to

smooth out the discontinuities that result from applying the FFT is to segments (i.e., windows) of

audio data. A simplifying assumption for the FFT is that each windowed segment of audio data

contains an integral number of cycles, this cycle repeating throughout the audio. This, of course,

is not generally the case. If it were the case – that is, if the window ended exactly where the

cycle ended – then the end of the cycle would be at exactly the same amplitude as the beginning.

The beginning and end would "match up." The actual discontinuity between the end of a

window and its beginning is interpreted by the FFT as a jump from one level to another, as

shown in Figure 2.51. (In this figure, we've cut and pasted a portion from the beginning of the

window to its end to show that the ends don't match up.)