Desenvolvimento de um sistema de controle digital para afinação de instrumentos de corda

Abstract

The acoustic quality performance of an musical instrument is related to its correct tuning. However, the tuning of string musical instruments varies over time due to environmental and natural factors. Therefore, the musician must constantly check the tuning, which requires technical knowledge and time. Thus, the development of an automatic tuning system for string instruments had become necessary. Some commercial devices that ensure automatic tuning can be easily found in the market, for example TronicalTune and RoadieTuner, althought, they are not popular due to elevated price. In this project, an automatic tuning control system for acoustic string instrument was developed with accuracy, rapidity and low cost. Such system has a metal piece that fits on the tunning machine and by a software the user chooses the desired frequency for the chosen string. A microphone captures the acoustic signal produced by the string; after that, an analog input of the Arduino UNO reads that signal and by an autocorrelation algorithm estimates the fundamental frequency of the audio sample. Besides that, the Arduino is responsible for determining the difference between the frequency of the received signal and the frequency of the desired musical note. Two digital controls, PID and another one based on the system equation (obtained through a mathematical modeling), were implemented in the Arduino to calculate and send to the stepper motor the signal that sets the direction of rotation, stretching or loosening the string, and the amount of steps required for the string to be tuned. Experiments were performed using a ukulele, obtaining satisfactory results in time and accuracy. The system can be used by both beginner and advanced musicians and minimizes tuning time.