There is a modification to an original Game Boy that involves replacing the internal crystal oscillator with one of a different value, documented by the genius Gieskes. Often, a value of 2MHz is used to replace the default value of 4.194304 MHz because 2MHz crystals are easy to find in shops and on the internet, or at least thats what I do.However, this creates a problem, in the sense that the crystal oscillator is responsible for controlling all timing aspects of the Game Boy including the frequency pitches of the pulse oscillators.
via little-scale: Retuning an Underclocked Game Boy.
