Final Year Project Pat Hurney Digital Pitch Correction for Electric Guitars

Project Overview The aim of this project is to develop a method of digitally altering the pitch of an out of tune guitars signal to make it sound in-tune. Many amateur and professional guitarists have tuning problems during gigs and rehearsals. This system should help eliminate a lot of these problems. Many guitarists like to use different tuning.

Steps in Project Develop a tuner that detects which note has just been played. Develop digital filters that can alter the pitch of a note by a certain amount. Test the filters on recorded guitar samples. Embed the filters on a DSP board. Use the filters with a guitar in real time. On one string at first and progressing on to other strings afterwards. Develop a GUI to let musicians develop new tunings to be used with their guitars.

Hardware/Software to be used Hardware  DSP Board  Guitar Software  Matlab  C  JAVA

Start Is tuner calibrated Determine String used Obtain Pitch of note Compare Pitch of note to reference notes Determine Difference in notes Store Difference Correct note No Determine String used Are reference notes set Set reference notes Yes No Yes

Block Diagram of Un-calibrated System Pitch Detection Pitch Comparison Pitch Correction Reference Pitches Pitches set in GUI Guitar Signal String Detection Pitch Offset

String Detection Piezo pickups will be used here. Each string will have its own pickup that will output the signal from that string to the DSP board. Piezo pickups have a very different tone to standard pickups which could be a problem.  One solution will be to use the signal from the piezo pickups to determine how much the signal from the guitars main output needs to be altered by.

Pitch Detection Pitch Detection will be done by using an FFT to determine the fundamental frequency of the note played. A suitable pitch detection algorithm will then be used to obtain the pitch. The guitar signal contains a number of additional harmonics. Up to five peaks were found on each signal after a FFT. A sampling rate of 44.1kHz will be used. This is to ensure that a large amount of harmonics are preserved in the sampled signal. Pitch Detection will first be done with single notes on one string. More then one note will be used later in the project.

Pitch Comparison The difference in the guitar signal’s pitch and the reference notes pitch will be calculated here. This will be done by comparison of the FFT’s of the guitar signal and the reference sample. More research needs to go in to this area.

Pitch Correction The pitch of the signal will be modified here without affecting the time-scale of the frequency. A phase vocoder will be used in the pitch correction as this allows modification of the pitch without altering the time-scale. Research has shown that this has been used in live performances for pitch correction for vocals.

Questions?