The barber changed the tonal quality of a pungi into the melodious voice of shehnai through a process called 'voicing'.

Voicing is the process of adjusting and manipulating the reed of a wind instrument to create a desired sound. In this case, the barber would have adjusted the reed of the pungi to create a sound that is closer to the shehnai.

The process of voicing can be broken down into the following steps:

1. Adjusting the reed: The barber would have adjusted the reed of the pungi to create a sound that is more similar to the shehnai. This involves making changes to the length and thickness of the reed.

2. Adjusting the mouthpiece: The mouthpiece of the pungi would have also been adjusted to create a sound that is closer to the shehnai. This involves making changes to the size and shape of the mouthpiece.

3. Adjusting the toneholes: The toneholes of the pungi would have been adjusted to create a sound that is more melodious. This involves making changes to the size and placement of the toneholes.

4. Testing the sound: Once the adjustments have been made, the barber would have tested the sound to ensure that it is closer to the shehnai. This may involve playing different notes and adjusting the voicing as necessary.

In summary, the barber changed the tonal quality of the pungi into the melodious voice of shehnai through the process of voicing, which involves adjusting the reed, mouthpiece, and toneholes of the instrument to create a desired sound.

He took a hollow stick and he then put holes on the stick due to which melodious sound came