Final Year ProjectPat 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

HardwareDSP BoardGuitar

SoftwareMatlab CJAVA

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

DetectionPitch 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?