tBeepr - ZX Spectrum beeper music engine
Original Z80 code by introspec, 1995, 2013
1tracker version by Shiru, 2013, 2015


tBeepr is a beeper music engine for ZX Spectrum that was designed in the 
mid 1990s for the game 'Tank Battle'. The original version of the engine 
was written by cross-breeding few ideas from the two-channel beeper 
engine found inside of Wham The Music Box by Mark Alexander and the 
David Whittaker's two-channel engine with interrupting drums (as found 
in the first Dizzy game). The present version of the engine was 
recovered from the old (incomplete) sources, cleaned up, re-tuned and 
slightly expanded, to make it a reasonably well-featured modern engine. 

The engine provides two channels of tone with 5 settings of duty cycle 
and crude duty cycle envelope; and interrupting drums. 


The columns are:

T1 dE T2 dE Dr
..... ..... ..
|   | |   |
+ch1+ +ch2+

T1,T2 : Tone channels
 Tn : Note, D#2..E-6
  d : Duty cycle, 1..5, (~0%, 25%, 50%, 75%, ~100%)
  E : Envelope, 1 enable, 2 disable
