What causes Timber or different quality of sound in different instunmnts?What is the physical quantitiy that determines the quality of sound?
Sound produced is dependent upon the mass (per unit length ) and tuning tension of the string and on other factors of the musical instrument. Like for Guitar thicker, heavier strings produce lower pitch tones (lower frequency) than thinner, lighter strings that produce higher pitch (higher frequency).
In simple terms, timbre is what makes a particular musical sound different from another, even when they have the same pitch and loudness.
Sound quality or timbre describes those characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness. Timbre is then a general term for the distinguishable characteristics of a tone.