Signals

• Functions are mappings on sets.
• Signals are functions that represent information.
• Audio signals are mappings from time to air pressure.
• Audio signals represent sounds perceived by humans.
• An image is a mapping from a region of space to light intensity.
• Images carry information perceived through human vision.
• A radio signal is a mapping from time to electromagnetic waves.
• Radio signals carry information of all types, but must be converted to be perceivable by humans.
• An event trace is a mapping from indexes to events.
• Event traces carry information about discrete actions.