Add missing file

Author: tversteeg

src/theory/sound.md

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+# Sound
+
+Sound is a medium (air), vibrating.
+
+Us humans make a distinction between sound and noise:
+
+When air is displaced in certain patterns our brains can recognize, we call it sound.
+When air is displaced in patterns our brain _can't_ recognize, we call it noise.
+
+### Speakers
+
+To generate sound from an electronic device we need something we commonly call a speaker.
+
+A speaker works by converting electronic current to movement to vibrate air. 
+
+![Sound](https://upload.wikimedia.org/wikipedia/commons/8/82/CPT-sound-physical-manifestation.svg)
+
+This electronic current is an analog signal, which means that it also has a wave pattern unlike a digital signal, which is an off-or-on current, 0's and 1's.