In music, the tone colour, or quality of tone, of a particular sound. Different instruments playing a note at the same pitch have different sound qualities, and it is the timbre that enables the listener to distinguish the sound of, for example, a trumpet from that of a violin. The tone quality of a sound depends on several things, including its waveform, the strength of its harmonics, and its attack and decay – the ‘shape’ of the sound. The study of the elements of sound quality is part of the science of acoustics.
Sound production The characteristic tone quality of any instrument or voice is dependent on a number of factors: the various means of producing sound – for example, vibrating strings or reeds; their methods of excitation – such as plucking, bowing, or blowing; and means of amplification – either mechanical, such as a soundboard, or electrical. These differences have their effect on the waveform, the mixture of harmonics, and the envelope shape of the sound.
Analysis of waveform By means of an oscilloscope, sounds can be represented visually, and an accurate analysis made of certain of their component parts. Most immediately apparent from these visual representations is the complexity of seemingly simple sounds: picking out the characteristics that distinguish one instrumental colour from another is not easy. Many complex waveforms can be seen as mixtures of pure tones, and in musical sounds as mixtures of harmonics in particular. The two principal parameters of sound – frequency and amplitude – are used in the analysis of timbre to describe the presence and relative strength of the harmonics that make up the sound in its ‘steady state’, that is, when playing a sustained note. Instruments such as the recorder and flute have tones that are comparatively ‘pure’, with only a few weak harmonics above the fundamental tone; whereas the double reed instruments such as the bassoon and oboe have complex tones, rich in higher harmonics.
Sound shapes Analysis of a sound in its steady state alone, however, does not completely define its timbre. Equally important is the overall shape of the sound: its starting transient (attack) and envelope shape (the steady state and subsequent decay), which can be studied with the aid of spectrum analysers such as sonagraphs, or real-time analysers. Experiments have shown that recordings of an instrument playing a sustained note, minus its initial attack, are very difficult to identify. Variations of amplitude during the course of a note and the speed with which they occur have a major effect on timbre. A sound may start very quietly and comparatively slowly reach the volume of its sustained tone, as with the flute; or it may begin almost immediately at maximum volume and quickly die away, as does the plucked string of a harpsichord. These changes in amplitude also affect the waveform during the note, as the harmonics may increase or decrease in volume at different rates – thus a note may have a noticeably different timbre at different stages of its production, and even a perceived difference of pitch. There may also be slight variations in frequency in some notes, particularly when some form of vibrato forms an important part of the timbre.
Elements of music
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