Pulse Width Modulation, is a DAC (Digital Analog Convertor)<br />
Using a entry clock, you output a signal 0v or 5v in order to result an average fix value between 0v and 5v, for sample 2.3v. Changing like it the speed of a small electric motor as you want but using at input only two values : 0v or 5v.
Using a quicker clock, you can generate analog signal, like sound music.
end PWM_arch;
Ok, let's go further, let's target 2.5v using only 0v and 5v, with a stupid slow clock, you result in a sequence like this : 05050505050505v. It is a bad border effect : it a noise ! 2.5v normaly doesn't produce sound by here, but using this simple PWM it does.<br />
This problem is solved here : this is an original homemade PWM component enabling Arkanoid not producing noises instead of silents, don't ask me how I solved it two years ago but it does :