I want to control the volume of the output using Sound command.

[HenrikOlsson]

I don't see the need for an interrupt for what you're doing there.

X = 5
Start:
   HPWM 3, X, 20000
   SOUND PortC.3, [255, 5]   ' Make sound for ~60ms
   X = X + 5
Goto Start

Though I'd probably setup the CCP module manually and write to the dutycycle register instead of using the HPWM command since I Believe you'll get some discontinuties in the output when constantly changing the dutycycle using HPWM - may be wrong on that and/or it may not matter in your case, try it.

/Henrik.

[billys7]

Totaly, i have tried all the methods you have suggested me, unfortunately the results wasn't so good.
In every case, there was a small interrupt on the sound.

I decided to produce the white noise by an external small circuit, and then to process it with PWM.

Thank you all.