| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 107 === In the past, the tristimulus was used for the timbre analysis of musical instruments. The intensity ratio between the fundamental oscillating mode and the overtones are used to define the coordinates in the tristimulus. The timbre can be approximately classified by the coordinates.
In this study, we found that the different types of the vibration decay of the string at the fundamental frequency could significantly result in the different timbres. In our experiment by exciting the first, second and third strings of the classical guitar, at the fundamental frequencies, two types of decay, exponential decay and non-exponential decay, can be observed in the recorded sound. Different timbres can be sensed. Therefore, this study is aimed to understand the physical origins to excite the non-exponential decay of sound of the string of the classical guitar at the fundamental frequency. We suppose that the different types of string vibration decay result from the non-uniform force as the string slices on the rough surface of the nail. We use the finite element analysis method to simulate the vibration of the first string of the classical guitar under the different non-uniform excitation forces. The short-time Fourier transform (STFT) of the vibration is applied to analyze the vibration decay at the fundamental frequency. The significant frequency shift is observed. In this work, the sound of strings of a home-made classical guitar is recorded using an artificial finger controlled by a motor to pluck the strings. The exponential and non-exponential decay of the recorded sound can is observed. The origins of the non-exponential decay are exempted from the non-uniform forces induced by the nail supposed in the simulation of this study.
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