Unfortunately, this very sharp switching on and off inherent to the square-waveform causes extremely high frequency vibrations in the lamp. A square wave can be thought of as an infinite sum of odd-numbered harmonics, which will include frequencies at the resonant frequency of the bulb, causing it to vibrate at that frequency like a bell or whistle. The lamp housing does not help this, acting as a resonating chamber that amplifies the noise and presents a problem for sync-sound recording for film and video. To correct this, most electronic ballasts are equipped with a "silent mode" that eliminates the higher frequencies, but rounds off the voltage transition, causing the same flicker issue with magnetics, though to a lesser extent. This mode provides safe, flicker-free filming at framerates up to "24 frame/s" on most electronic ballasts.