a device for encoding the expression of a keyboard percussive instrument is disclosed . the apparatus places a suitable ac voltage on a coating applied to a hammer and positions a pair of capacitive coupled pads near the string to be struck by the hammer . as the hammer sweeps past the pads , signals are capacitively coupled from the hammer motion to the pads . suitable latches are set and unset to form a signal which is coupled through a switch , a sample and hold amplifier , then to an analog to digital convertor which forms an expressive signal of n bits length . the signal is begun by depression of the key and is terminated by closure of the key upon release by the musician , the key of the instrument being provided with capacitive pickup pads coupled to the key and through a reset gate to the latches . alternate embodiments are additionally disclosed .