Also called filament-hum or buzz, is a phenomenon of the clipped waveform of all phase-control dimmers. Higher wattage lamps are usually more susceptible, as are PAR56 and 64 lamps of all wattages. The latest sine-wave dimmers, which work by altering the amplitude of the sine-wave rather than clipping it, eliminate this problem. Some concert halls, where ALL environmental noise is a distraction, are installing sine-wave dimmer today, with variable results. It has been suggested that Sine Wave Dimmers are "the party the dimmer manufacturers gave, but nobody came" --[USER]STEVETERRY[/USER], in the USA. Due to cost, and sometimes lack of reliability and poor design in early implementations (even by a well-known manufacturer), market uptake of Sine Wave dimmers in the USA has been minimal. See also this article from the ETC wiki: Risetime and Lamp Noise - What's the Connection? and the CB wik entry dimmer rise time.