The sound you are referring to is a combination of several sounds together. The racquet moving through the air, the strings contacting the ball, the strings brushing the ball and the ball expanding after being compressed with the latter contributing most to the pop.
The flatter you hit the more the ball will compress/decompress and the less of the higher pitched ffffft sound will be heard from applied spin but a good hit with some ts can also get that sound.
To accomplish this you need the right combination of rhs, force from weight and leverage on the ball and a favorable angle of impact. In other words a well struck ball. This happens when you have a loose grip for rhs, proper weight going into the ball and good contact w/o too much spin.
If you have to ask how to get this sound that means you are not proficient in the above skills at this time.