Nonperiodic, one-off signals require analysis tools beyond the Fourier series.

Evidence

The Fourier series is useful for analyzing periodic signals. However, many signals are nonperiodic; that is, they only occur once. This requires a different approach. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2757

Categorization

• DEFINE: Draws the periodic/nonperiodic distinction that motivates the Fourier transform later in the appendix.