A musical instrument is a device constructed or modified with the purpose of making music.In principle anything that,produces sound,and can somehow be controlled by a person playing it,can serve as a musical instrument.The expression,however,is reserved generally for items that have a specific musical purpose.The academic study of musical instruments is called organology.
Voice,that is,the human voice,is an instrument in its own right.A singer generates sounds when airflow from the lungs sets the vocal cords into oscillation.The fundamental frequency is controlled by the tension of the vocal cords and the tone quality by the formation of the vocal tract; a wide range of sounds can be created.
String instruments generate a sound when the string is plucked,strummed,slapped,etc.The frequency of the wave generated (and therefore the note produced) usually depends on the length of the vibrating portion of the string,its linear density (mass per unit length of string),the tension of each string and the point at which the string is excited; the tone quality varies with the construction of the resonating cavity.Examples:guitars,violins and sitars.