Tonewheel

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A tonewheel is a relatively primitive apparatus for generating electronic musical notes. The tonewheel assembly consists of a synchronous AC motor and an associated gearbox that drives a series of rotating disks. Each disk contains a set of bumps that generate a specific frequency through a corresponding pickup assembly, consisting of a magnet and coil. The frequency depends on the speed of rotation of the disk and the number of bumps. A single fundamental frequency can be combined with one or more harmonics to produce complex sounds. A tonewheel was used in the Teleharmonium and in the original Hammond organs.

Tonewheel leakage occurs in the Hammond organ and in similar situations, where the large number of tonewheels causes pickups to overhear tonewheels other than their own. This causes the organ to produce chromatic harmonics. Mostly this is bad, but in some genres it has become an important part of the Hammond sound. On some digital simulations of Hammond organs tonewheel leakage is a user-set parameter.