This document discusses digital signal processing concepts including: 1) Basic types of digital signals such as unit impulse sequences and unit step sequences. 2) Linear time-invariant (LTI) systems and their properties including causality and stability. LTI systems can be represented using impulse responses. 3) Convolution, which is used to analyze LTI systems in the time domain by representing the output as a sum of delayed and scaled impulse responses of the input.