When someone speaks across a room, the air does not travel to your ear: each layer pushes the next and swings back, and the push runs outward at 343 metres a second until it moves your eardrum by less than an atom — run on the page: vibration, waves and decibels; echoes, sources, resonators and the sea; spectra, meters and digital audio; the ear, loudness, speech and animal sound; strings, winds and tuning; rooms, halls and walls; noise, loudspeakers and ultrasound. Drive a wave, tune a pipe, take a vowel apart and quieten a street — every number computed by the page, every sound synthesised and played quietly.
Every curve and number on these pages is computed by the page or cited with its source, and every sound is synthesised on the page; your progress stays in this browser. Set your device volume low before you press play: sounds start quiet, fade in and out and stay under a ceiling, and loud sounds are shown, never played at level. Nothing here tests your hearing — hearing problems are for a doctor or audiologist. The course gives no medical, legal or engineering advice and names no product. Not affiliated with or endorsed by any organisation, manufacturer, publisher or author mentioned here.