Vitamin A is a group of unsaturated nutritional organic compounds, that includes retinol, retinal, retinoic acid, and several provitamin A carotenoids, and beta-carotene. Vitamin A has multiple functions: it is important for growth and development, for the maintenance of the immune system and good vision.itamin A can be found in two principal forms in foods 1  : Retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble substance. 2  Since the pure alcohol form is unstable, the vitamin is found in tissues in a form of retinyl ester.
pure tone is a tone with a sinusoidal waveform reciting tone such as psalm tone and recitative as in gregorian chants timbre the quality of a musical note or sound that distinguishes different types of sound production tonality a system of music based on a key center or tonic tone control a typically electronic control for affecting frequency content of an audio signal tone linguistics the pitch and pitch changes in words of certain languages tone musical instrument the audible characteristics of a musician s sound
The sound of a musical instrument may be described with such words as bright, dark, warm, harsh, and other terms. There are also colors of noise, such as pink and white. In visual representations of sound, timbre corresponds to the shape of the image (Abbado 1988, 3).