Signal processing techniques to analyze the effects of guitar geometry on musical timbre

Abstract

Musical acousticians seek to answer many questions. What makes a particular instrument sound like it does? How do listeners perceive musical sounds? As an undergraduate design project, three guitars of varying shapes (‘‘box,’’ ‘‘triangle,’’ ‘‘octagon’’) were constructed and then compared to the traditional design. Materials were not varied, only the geometry of the sound boxes. The overall volume of each sound box was approximately equal. Digitized samples of the plucked strings of the constructed and traditional guitar were obtained. Conventional Fourier signal analysis of the notes from the three constructed guitars showed similarities to those of the traditional guitar. Other signal processing methods, such as short-time Fourier transform spectrograms, appropriate for the transient signal of the plucked string, were also investigated. Although the signals were broadly similar, analysis revealed differences, which might be attributed to the different geometries. A survey was conducted to assess listener’s preferences for the various instruments. The survey was conducted from taped samples of the plucked strings to correlate the importance of psychoacoustics and the physical signal in assessing instrument quality. Listener preference rated the octagon-shaped guitar as highly as the traditional one. [Work supported by the Loyola College Department of Electrical Engineering and Engineering Science, and the Loyola College Hauber Fellowship Fund.]