Designing an Automated Guitar Tuner: An Exercise in Control Theory

What?
Using knowledge of control theory, a partner and I attempted to build an automated guitar tuner. This turned into a study of phase-locked loops, which we proved were not a possible solution to the automated guitar tuner problem.
Why?
An automated guitar tuner is useful because many amateur guitar players do not have a good sense of pitch and take several minutes to tune before playing. An automated guitar tuner would tune the guitar in seconds.
How?
Rather than using a microphone and a digital control system, which we supposed would be too imprecise, we decided to try to use a phase-locked loop in analog circuitry to control our system. Unfortunately, the need for filters and an automatic gain control circuit (since a guitar sound fades quickly) make the system impossible to control with this architecture, as our final paper explains.
Using knowledge of control theory, a partner and I attempted to build an automated guitar tuner. This turned into a study of phase-locked loops, which we proved were not a possible solution to the automated guitar tuner problem.
Why?
An automated guitar tuner is useful because many amateur guitar players do not have a good sense of pitch and take several minutes to tune before playing. An automated guitar tuner would tune the guitar in seconds.
How?
Rather than using a microphone and a digital control system, which we supposed would be too imprecise, we decided to try to use a phase-locked loop in analog circuitry to control our system. Unfortunately, the need for filters and an automatic gain control circuit (since a guitar sound fades quickly) make the system impossible to control with this architecture, as our final paper explains.