tuning
The process of adjusting an instrument's pitch to a standard reference or to match other instruments.
In Depth
Tuning ensures that an instrument produces the correct pitches. The standard reference pitch is A4 = 440 Hz, though some orchestras tune slightly higher (the Berlin Philharmonic uses A = 443 Hz) for a brighter sound. Before a concert, the oboe sounds the tuning A and all other instruments adjust to match.
Different instruments are tuned differently. String instruments tune their four (or more) strings to specific intervals. Wind instruments are tuned by adjusting the length of the tubing. Pianos are tuned by a specialist using a tuning fork or electronic device, adjusting the tension of each of the instrument's approximately 230 strings — a process that takes 1-2 hours.
A piano has approximately 230 strings under a combined tension of about 20 tons — roughly the weight of a large truck. The cast iron frame that holds this tension is the heaviest single component.