startip2.py

# Author: Peter Sovietov

from __future__ import division
import struct
import wave

SR = 44100

def write_wave(filename, samples):
  f = wave.open(filename, "w")
  f.setparams((1, 2, SR, len(samples), "NONE", ""))
  f.writeframes(b"".join(
    [struct.pack('<h', round(x * 32767)) for x in samples]))
  f.close()

def decimate(samples, m):
  x_pos = 0
  x_delay = [0] * m
  y = 0
  for i, x in enumerate(samples):
    y += x - x_delay[x_pos]
    x_delay[x_pos] = x
    x_pos = (x_pos + 1) % len(x_delay)
    samples[i] = y / m
  return samples[::m]

M = 32
ON = 0.5
OFF = 0
T1 = 6
T2 = 54

def out(samples, x, t):
  samples += [x] * t

def engine(samples, dur, t1, t2, vol, periods):
  counters = periods[:]
  t1_counter = t1
  t2_counter = t2
  update_counter = t1
  width = 1
  is_slide_up = True
  for d in range(dur):
    for i in range(3):
      counters[i] -= 1
      if counters[i] == 0:
        out(samples, ON, width * T1)
        out(samples, OFF, (16 - width) * T1)
        counters[i] = periods[i]
    update_counter -= 1
    if update_counter == 0:
      update_counter = 10
      if is_slide_up:
        t1_counter -= 1
        if t1_counter == 0:
          t1_counter = t1
          width += 1
          if width == 15:
            width = 14
            is_slide_up = False
      else:
        t2_counter -= 1
        if t2_counter == 0:
          t2_counter = t2
          if width - 1 != vol:
            width -= 1
    out(samples, samples[-1], T2)

def play(samples, frames):
  dur = 0
  vol = 0
  t1 = 0
  t2 = 0
  i = 0
  while frames[i] != 0:
    if frames[i] == 0xff:
      dur = frames[i + 2] << 8 | frames[i + 1]
      t1, t2, vol = frames[i + 3:i + 6]
      i += 6
    else:
      engine(samples, dur, t1, t2, vol, frames[i: i + 3])
      i += 3

samples = [0]

with open("startip2.txt") as f:
  frames = [int(x, 16) for x in f.read().split()]
  play(samples, frames)

write_wave("startip2.wav", decimate(samples, M))