Named for the latter two researchers as amplitude envelope, other factors such as fluctuations in volume and height, the spectral distribution (amplitudes of the frequencies of the spectral components) and the evolution time involved in
timbre perception not only of musical instruments, but also voice human.
To understand this evocative force, researchers in many fields, including information science, neural
perception, and signal processing, investigate music's underlying structure, examining features such as the tone,
timbre, and auditory and rhythmic features of a piece.