Embodiments of the keyboard system that can determine accurate key operation. The system provides immediate processing of the data input streams from various strike sources, the key stroke depth data, the key strike speed data, the key strike acceleration data. The movement state volume V can be calculated using a formula shown below, based on the key strike depth D, the key speed S, the key acceleration A, the coefficient a, b, c, and constant d. V=a*D+b*S+c*A+d. When the volume level exceeds the predetermined level A, the system determines that the key has been pressed. When it is determined that the key has been pressed, the “note-on” information is outputted to the sound source. The velocity value included in the “note-on” information is calculated with reference to the velocity curve based on the key speed when it is determined that the key has been pressed.