The final Signals and Systems lecture explains how audio playback evolved from the fragile Edison cylinder phonograph to durable modern optical disks, through the application of digital signal processing concepts.

Continuing the previous discussion of AM in radio, Prof. Freeman analyzes phase and frequency modulated (PM/FM) signals, before presenting research showing improvement in optical microscopy via phase-modulated illumination.

Efficient signal transmission and reception requires wavelengths matching the size of the antenna; for speech, this requires frequencies around the GHz range. Broadcast radio developed AM and FM to produce accurate reception of multiplexed signals.