Textbook in PDF format Theory, is an introductory textbook on the analysis of signals in time and frequency. It takes an engineer’s perspective and discusses how to characterize, analyze and operate on signals. The basic theoretical concepts, Fourier series and transform, are explained in continuous time. It then introduces discrete-time signals, addressing how sampling and finite signal duration affect spectral analysis. It discusses the discrete Fourier transform and its use in spectral estimation. The book concludes with an introduction to linear systems and signal filtering