| Summary: | Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. === Cataloged from PDF version of thesis. === Includes bibliographical references (p. 36). === Timbre describes the perceptual difference between sounds with the same loudness and pitch generated from different sources such as different instruments. Each instrument has its own unique timbre making it distinguishable. Within each instrument however, this timbre changes slightly with respect to frequency and intensity of sound. This is perceived qualitatively by the use of words such as "bright", "mellow", "harsh" and many others to describe sounds of different intensity or frequency in a given instrument. However, this is only a subjective view and does not describe what changes in the acoustic properties produce these different timbres. This study quantitatively examined the change in timbre over the frequency and intensity range of the French horn. Two main acoustical properties were measured: number of frequency partials and shape of the spectral envelope, where "partials" refers to harmonics of the fundamental frequency. The parameter represented by the number of partials includes both the total number of partials as well as the number of partials with critical band overlap. The shape of the spectral envelope was characterized through its center frequency and width of the major peaks as well as the strength of the fundamental frequency. Each of these parameters was related to qualitative timbre descriptions such as "fullness" or "roughness". The results showed a significant change in timbre over the frequency and intensity range of the French horn. The extremes of French horn span from timbre that is "thin" and "smooth" to "rich" and "rough". Within this spectrum, low frequency notes and high intensity sounds lie at one end exhibiting "rich" and "rough" timbre. The high frequency and low intensity sounds lie at the other extreme exhibiting "thin" and "smooth" timbre. As frequency increases and intensity decreases the number of partials decreases and the spectral contour shifts from wide and flat to a strong narrow peak. This produces a timbre shift from sounds that seem "rough" and "rich" to those that seem "smooth" and "thin". === by Kathryn E. Shroyer. === S.B.
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