How sound is produced in Musical Instruments?

How is sound produced ?

Explain how sound is produced in humans.

Assertion (A): The musical notes produced by two musical instruments, like guitar and sitar are different even if the length and the thickness of the strings in both instruments are the same. Reason (R) : The difference in two sounds of equal pitch and loudness can be distinguished by a characteristic property called quality of sound ro timbre.

How are different musical notes produced in stringed instruments, in musical instruments having stretched membranes and in musical instruments of blow type ?