Waves contain information about change in the form of energy generated by the change. They have the ability to do work and that is what we count on to produce out artifacts.

There is a chain of energy transfers from the original medium or event to:

Some kind of detector (microphone, camera)

Some kind of recorder (DAT, Cassette, the "corder" part of camcorder)

Some kind of processor (editing, developing)

Some kind of transmitter (radio station, projector)

Some kind of receiver (receiver, screen, speakers)

Back to the original medium or waveform (sound or light)

Then to a human receiver (audience).

At every phase there is a transformation or transfer of energy:

Electrical to mechanical (electromechanical)

Light to electricity (photoelectric)

Light to chemical (photochemical)

Electrical to magnetic (electromagnetic)

Magnetic to mechanical

Almost any combination you can think of

The devices that do that are called transducers. Lets look at some for audio to:

Demystify some technology

Understand why we cannot have perfection

See what can go wrong.

Illustration

Electromagnet made from a wire, a battery, and a nail. Introduce current and the nail becomes magnetized.

Remove battery. Attach electric meter. Remove nail. Replace with magnet. Meter moves when magnet moves.

Illustration (how about a GIF animation here? Moving magnet and meter)

This is the essence of the most basic microphone (and speaker for that matter)

Illustration

The air (medium) conducts the wave (patterns of energy, information) toward the microphone where the wave displaces the diaphragm in a pattern that matches the energy pattern of the wave. The microphone generates electrical patterns that are analogous to the wave pattern. Reverse the process and you have a speaker. Most transducers can work backward or forward.

Illustration

Piezoelectric: Some transducers change shape when they are subject to electrical impulses. In reverse, they produce electricity when they are deformed. This is the mechanism underlying the phonograph record.

Illustration

The most common way of recording and reproducing information in the world uses one of the most vulnerable media to read/write. Cassettes, video, computer drives, diskettes, bankcards, magnetic film, and much more. The read/write (record) heads on these devices are electromagnetic transducers. Two principles are used.

Electromagnetic transduction

Magnetic polar attraction. (Opposite poles attract, like poles repel).

Illustration

Photoelectric easy to associate with film and video but what about audio. Some devices emit electrical signals when struck by light. The more light, the more electricity following the pattern of the light as it changes. (The reverse is also true; some devices like LEDs emit light when electrified.)

Optical sound negatives in film use this principle.

Illustration