Digitalizador de guitarra

Abstract

This work presents a complete system for electric guitar signal acquisition and processing, in order to translate the raw audio signal to the corresponding musical notes. It is important to mention that, while this is relatively easy to be accomplished in instruments that have separated keys for each note (e.g. piano), this is not the case for instruments like the guitar – the one addressed in this work – that have a single output for multiple notes (each string has about 15 notes). The guitar is a harmonic instrument, as it can play multiple notes simultaneously, making the translation a challenging task. It is difficult because multiple notes might be played at the same time and event the same note at different strings.The proposed approach employs a specially designed pickup, developed and constructed by the authors, with dedicated coils for each string (in contrast to the single coil regular models). Audio amplifiers based on INA326 OPAMPs condition the coils’ signals, which are further converted to digital by an acquisition module based on an ARM Cortex M3 microcontroller, model STM32F103C8T6. The digital samples are transferred to a PC through the USB bus and processed using pitch detection algorithms. The software is based on contemporary tools such as Node, NW.js, React+Redux and Functional Programming. Special emphasis has been dedicated to the applied nature of the project, in the sense that the goal was to obtain a ready-to-use prototype, despite the limitations on the accuracy of the final translation. In other words, the present work does not focus on state-of-the-art signal processing approaches in order to obtain a near perfect translation. Instead, it prioritizes an effective hardware and software architecture aiming a completely functional system for real-time guitar signal translation into the corresponding notes. Two pitch detection algorithms were evaluated: YIN and McLeod. Results show that each algorithm has their own strong and weak points, as both must be considered in the future.