Acoustics Researchers Decompose Sound Accurately Into its Three Basic Components
hubie writes:
Researchers have been looking for ways to decompose sound into its basic ingredients for over 200 years. In the 1820s, French scientist Joseph Fourier proposed that any signal, including sounds, can be built using sufficiently many sine waves. These waves sound like whistles, each have their own frequency, level and start time, and are the basic building blocks of sound.
However, some sounds, such as the flute and a breathy human voice, may require hundreds or even thousands of sines to exactly imitate the original waveform. This comes from the fact that such sounds contain a less harmonical, more noisy structure, where all frequencies occur at once. One solution is to divide sound into two types of components, sines and noise, with a smaller number of whistling sine waves and combined with variable noises, or hisses, to complete the imitation.
Even this 'complete' two-component sound model has issues with the smoothing of the beginnings of sound events, such as consonants in voice or drum sounds in music. A third component, named transient, was introduced around the year 2000 to help model the sharpness of such sounds. Transients alone sound like clicks. From then on, sound has been often divided into three components: sines, noise, and transients.
The three-component model of sines, noise and transients has now been refined by researchers at Aalto University Acoustics Lab, using ideas from auditory perception, fuzzy logic, and perfect reconstruction.
Doctoral researcher Leonardo Fierro and professor Vesa Valimaki realized the way that people hear the different components and separate whistles, clicks, and hisses is important. If a click gets spread in time, it starts to ring and sound noisier; by contrast, focusing on very brief sounds might cause some loss of tonality.
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