prdr - ZX Spectrum beeper music engine
Original Z80 and 1tracker version by Shiru 08'15



This simplistic engine uses periodic noise with short periods (2-256) to 
generate different tones and noises. It only has two channels without 
drums, but also supports slide down, allowing to imitate various 
non-interrupting drum sounds using tone channels. Additionally, channels 
has different volume to create more dynamic sound. 


The columns are:

Sp T1 dPSl T2 dPSl
.. ....... .......
   |     | |     |
   +-ch1-+ +-ch2-+
   
Sp : Speed, 1..99

T1,T2 : Tone channels
 Tn : Note, F#1..B-7
  d : Detune, 1..9
  P : Period, 1..8 (remains active for all subsequent notes)
 Sl : Slide speed, 1..98, 99 to disable (remains active too)
 