POWW - ZX Spectrum beeper music engine
written by utz 05'2013
1tracker version by Shiru, 2013


The engine provides two channels of tone, one of them uses PWM-based 
waveforms and another is plain square tone. There is two drum sounds as 
well. 

The engine has global speed, no loop support, two drum sounds, rest 
note. Song speed highly depends from note and waveform selected for the 
first channel and may vary depending from these. 


T1 d W  T2 d D
.... .. .... .
|     | |  |
+-ch1-+ +ch2

T1,T2 : Tone channels
 Tn : Note, G-2..B-6
  d : Detune, 1..9
  W : Waveform, 1..10 (ch1 only)
  
 D : Drum, 1..2
