Timbre is the quality of a sound. Different qualities of sound help us to distinguish the sounds of different instruments. For example, although the flute and the oboe are both wind instruments, their distinctive sounds are very different from one another. If a flute and an oboe play the same tune, the characteristic timbre of each instrument distinguishes one from the other, regardless of the dynamic level at which they are played.
Picture Courtesy of Yamaha
Picture Courtesy of Yamaha
Timbre is sometimes referred to as tone color. It has been said that timbre is to music as color is to visual art, because the range of sounds in music is as broad as the range of colors in the visual arts. Likewise, timbres of instruments that belong to different classes differ as much as contrasting colors. It is not difficult to distinguish between the timbre of a trumpet and a violin, for example. Even if you don't know the names of the instruments you are hearing, the sounds themselves are distinct enough to be recognized as produced by different sound sources.
What causes different timbres? To a great extent, the shape of the sound waves produced by a voice or instrument determines timbre. Thus, we generally speak of vocal or instrumental timbres. Incidentally, because humans used their voices long before any instrument was ever made, it can be safely said that the human voice was the first instrument and therefore the first timbre.
In addition to sound wave shapes, another important factor that determines timbre is the way instruments are played, i.e., how the sounds are actually produced. The classification scheme in the table below divides instruments according to this criterion.
As you may have surmised, some instruments may be classified under more than one category. For example, an acoustic guitar with electronic amplification is considered both a chordophone and an electrophone.
A composer may write a piece to be either sung or performed by one or more instruments. Some pieces involve both vocal and instrumental timbres. Other times arrangements are made so that pieces composed for voice are played by an instrument, or pieces composed for a specific instrument such as the harpsichord are played using a different instrument, for example the guitar.
Sounds found in nature or the environment, such as birdcalls, train whistles, sea waves, or the patter of falling rain, are sometimes recorded and used by composers. These sounds have a timbre as well. Much as a painter has a whole palette of colors at his/her disposal, the infinite timbral palette offers composers an incredible range of sounds from which to choose.