At the bridge end of the guitar, each string of the guitar has a laser diode sat underneath it that sends out a beam parallel to each string towards the end of the fingerboard
If you've tried to digitally capture a guitar performance or turn your six-string into a powerful MIDI synth using an interface or special pickup, you'll no doubt be familiar with signal lag and pitch accuracy issues. As you pluck a string, there is a very short delay before it reaches its final frequency - it might only be a few milliseconds but it can be enough to cause latency angst. Germany's M3i Technologies has developed an optical system for accurately detecting the pitch of a string - even before a player has plucked it. The Laser Pitch Detection (LPD) Pickup system runs a beam under each string, from the bridge to the end of the fingerboard, and monitors its return to photosensitive receptors in the unit. When a player's finger touches a string, the beam is shortened and the system quickly measures and calculates the exact pitch.