The pitch, loudness, duration and timbre are the four qualities which define the structure of a piece of music. The pitch or the high-low aspect of the sound is considered to be the most important unit in structuring music. The timbre or the ‘tone colour’ is the sum total of the simultaneous motions produced by any vibrating medium. This is unique for each instrument. The timbre also defines the fineness of the sound produced by an instrument. Differences in timbre of sound produced by different instruments are responsible for the different musical qualities of the various instruments. Thus musical notes produced by different instruments sound different inspite of the pitch being the same.
