This document discusses discrete-time signal processing and audio signal processing. It covers topics like discrete-time signals, the z-transform, discrete Fourier transform (DFT) and fast Fourier transform (FFT). The key points are: - Audio signals are typically sampled at 44.1 kHz and quantized to 16 bits per sample. - The z-transform and discrete Fourier transform (DTFT) are used to analyze discrete-time signals in the transform domain, similar to the Laplace transform and continuous-time Fourier transform for analog signals. - The discrete Fourier transform (DFT) provides a computational tool to calculate Fourier transforms by sampling the frequency domain at discrete points, resulting in periodicity in the time and