I see, good to know but I was just experimenting with a range of capacitor value, from 6.8uF , 4.7uF, 3.3uF, 2.2uF, 1uF , but then I thought whether capacitor below 1uF exist, and found that one. even to 0.22 and 0.1uF, but below 0.47 seems the volume is too low and sometimes unheard so I think...