AntEater - ZX Spectrum beeper music engine
by utz 08'2014
1tracker version by Shiru 12'2017


Features two tone channels with detune support. One is a normal square 
wave tone, another is PWM modulated wave. Four click drums. Per-row 
speed. 

The name "anteater" is a reference to the game "Ant Attack" by Sandy 
White and Angela Sutherland, which is probably the first game on the 
Speccy to use pulse interleaving beeper sound. 


The columns are:

Sp T1 d T2 d D
.. .... .... .
   |  | |  |
   +ch1 +ch2
  
Sp : Speed, 1..63)

T1,T2 : Tone channels
 Tn : Note, D#1..B-7
  d : Detune, 1..9
  
 D : Drum, 1..4
