Timbre

Timbre is a complex notion that reflects the structure of the sound event in time and frequency. Exploration of the multi-dimensional space of timbre features is a subject of both psychoacoustic and artistic research. Several auditory attributes have been identified that allow listeners to discriminate basic aspects of timbre. For example, perception of mixtures of tones depends on their frequency differences and ratios: if the frequency difference is smaller than 15Hz, a single "fused" tone with pleasant beating (slow amplitude modulation) is detected, for more distant frequencies the fused tone becomes "rough", until a distance of critical bandwidth is reached, where it is replaced by a smooth sensation of two distinct tones.

Different complex mixtures of noise or tonal parts invoke different sensations of timbre, depending on the power distribution of the components in frequency domain (power spectrum or spectral density). For example, specific timbre of vowels in speech is a result of certain prominent frequency regions (peaks in the frequency domain) called formants.

An example sound spectrum exhibiting three distinct formants