Strike a virtual fork and hear it ring down naturally - the metallic ping, then seven seconds of pure reference tone. A440 by default; C256, A432, the medical C128, or any pitch you type.
ready to strike
The fork workflow that trained generations of musicians: strike, match your reference string (or voice) to the ringing tone until the beating between them disappears, then tune everything else by intervals from that anchor. The skill it builds - hearing beats vanish - is the foundation of the tune-by-ear method. Want a sustained tone instead of a decaying one? The A440 page holds the note forever; want a needle instead of your ear, the chromatic tuner listens through your mic.
It reproduces what a physical fork does acoustically: press Strike and hear a pure tone that starts with a soft attack and decays away naturally over several seconds, exactly like a struck fork ringing down. The pitch is digitally exact - an A440 fork here is 440.000 Hz, which physical forks (affected by temperature and wear) only approximate.
A440 - the A above middle C at 440 Hz, the international concert pitch. Other traditions persist: C256 ("scientific pitch") in physics teaching, C128 forks in medical exams (the low, long-ringing fork used for vibration-sense and hearing tests), and A432 among alternative-tuning enthusiasts.
Two classic exams: the 128 Hz fork tests vibration sense on bones (neuropathy screening), and the 512 Hz fork runs the Rinne and Weber hearing tests, distinguishing conductive from sensorineural hearing loss by comparing air and bone conduction. The tone itself is the same physics as this page - the bone-conduction part needs the physical object.
They train different things. A fork gives one perfect reference and makes your ear do the matching - which builds the skill. A needle tuner does the judging for you - faster, no skill required. Best practice: tune the reference string to the fork by ear, tune the rest by intervals, and verify with the chromatic tuner if you want confirmation.