In qawwali singing, there is a tradition of improvisational singing of the names of the musical notes in Urdu (“Do, Re, Mi, Fa, So, La, and Ti” are called “Sa, Re, Ga, Ma, Pa, Da, and Ni” in Urdu). Each name, like Sa, is sung in the pitch which it denotes, and it can be done very fast by some people. Here you can see the Pakistani master singer Nusrat Fateh Ali Khan improvising in the middle of a qawwali:
Another improvisation by Nusrat here.
See my first Saturday Qawwali Special at 3QD here.