Performance of Acoustic, Electro-Acoustic and Optical Sensors in Precise Waveform Analysis of a Plucked and Struck Guitar String

TL;DR

This study compares how well different sensors capture the vibrations of a guitar string when plucked or struck, showing that each sensor has unique strengths and limitations.

Contribution

The paper introduces a detailed comparison of acoustic, electro-acoustic, and optical sensors for guitar string vibration analysis under varied excitation conditions.

Findings

Microphones capture overall sound but lack spatial selectivity and have lower SNR compared to other methods.

Magnetic pickups offer accurate, cost-effective string-specific measurements but have limited temporal fidelity.

Laser Doppler vibrometers provide high temporal fidelity but alter string vibrations due to the optical target's influence.

Abstract

This study presents a comparative performance analysis of three sensor technologies—microphone, magnetic pickup, and laser Doppler vibrometer—for capturing string vibration under varied excitation conditions: striking, plectrum plucking, and wire plucking. Two different magnetic pickups are included in the comparison. Measurements were taken at multiple excitation levels on a simplified electric guitar mounted on a stable platform with repeatable excitation mechanisms. The analysis focuses on each sensor’s capacity to resolve fine-scale waveform features during the initial attack while also taking into account its capability to measure general changes in instrument dynamics and timbre. We evaluate their ability to distinguish vibro-acoustic phenomena resulting from changes in excitation method and strength as well as measurement location. Our findings highlight the significant influence of sensor choice on observable string vibration. While the microphone captures the overall radiated sound, it lacks the required spatial selectivity and offers poor SNR performance 34 dB lower then other methods. Magnetic pickups enable precise string-specific measurements, offering a compelling balance of accuracy and cost-effectiveness. Results show that their low-pass frequency characteristic limits temporal fidelity and must be accounted for when analysing general sound timbre. Laser Doppler vibrometers provide superior micro-temporal fidelity, which can have critical implications for physical modeling, instrument design, and advanced audio signal processing, but have severe practical limitations. Critically, we demonstrate that the required optical target, even when weighing as little as 0.1% of the string’s mass, alters the string’s vibratory characteristics by influencing RMS energy and spectral content.

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