There is a mplex factor that gives the speed of song.

the timer is called with 1193000 / mplex Hz
musics normally run with mplex 3000.

music resource:
  int16 size
  int16 xxx
  int16 pcjr_offset
  speaker resource
  pcjr    resource


speaker resource:
  byte  priority  (low 7 bit: priority, high bit: sound is delayable */
  byte  xxx
  int16 xxx
  speaker sound chunks...


/* SPEAKER sound chunks */
sound chunks:  several types, first word is type

chunk -1:  marks end of track

chunk -2:  marks start of loop
  next chunk starts immediately

chunk -3:  marks end of loop
  loop to last chunk -2

chunk -4:  reset sound system
  next chunk starts immediately

chunk 0:
  int16 mplex
 several blocks of either:
  int16 note-length
  int16 freq (plays a tone of 1193000/freq Hz)
 or:  
  int16 -5   (marks a variable (a script var?))
 or:
  int16 0    (end of chunk)


chunk 1:
  int16 mplex
  int16 start_freq
  int16 dest_freq
  int16 freq_delta
  int16 repeat_ctr

chunk 2:
  int16 start_mplex
  int16 dest_mplex
  int16 mplex_delta   /* speaker output is toggled on any interrupt */

chunk 3: (Complicated random noise)
  int16 start_mplex
  int16 dest_mplex
  int16 mplex_delta

  the mplex is anded with a LSR to produce random frequencies.
  


/* PCjr sound chunks */

pcjr resource:
  byte  priority  (low 7 bit: priority, high bit: sound is delayable */
  byte  xxx

chunk -1:  marks end of track

chunk -2:  marks start of loop
  next chunk starts immediately

chunk -3:  marks end of loop
  loop to last chunk -2

chunk -4:  reset sound system
  next chunk starts immediately

chunk 0:  music /* must be the first chunk! */
  int16 mplex
  int16 chan1_data  (offset from beggining of pcjr resource)
  int16 chan2_data
  int16 chan3_data
  int16 chan4_data

channel data:
  int16 a incr_volume_delta (attack)
  int16 b decr_volume_delta (decay)
  int16 c 
  int16 d
  int16 e

  n times:
   int16 notelen/4 
   int16 freq      (0: inter note pause)
  int16 endmarker  (-1: goto next chunk, -2: repeat this chunk)

abcde describe hull curve:

      ^
     / \b
   a/   -------\
   /      |     \
  /       c      \ d/(e+1)
 /        |       \
/         -        \---------

| 1  |2|  3    | 4  | 5

phase 4/5 are only used, when a pause occurs (freq=0).


chunk 1: (freq up/down) (must be first chunk)
  int16 mplex
  int16 offset_2nd_channel_data  (-1: not present)

  int16 first channel
  several times:
   int16 start_value
   int16 delta
   int16 length
  int16 -1  

2nd_channel_data:
  int16 first channel
  several times:
   int16 start_value
   int16 delta
   int16 length
  int16 -1  


chunk 2: (same as speaker chunk 2)
  int16 start_mplex
  int16 dest_mplex
  int16 mplex_delta   /* speaker output is toggled on any interrupt */

chunk 3: (generate noise)
  int16 mplex
  int16 noise_reg
  if ((noise_reg & 3) == 3)
    int16 noise_period (channel 2)
  int16 noise_volume
  int16 num_noise_vol_delta
  int16 noise_vol_deltas
  int16 ...



sounds in demo levels:

6 8 9
11 12 

sound 13!
chan1 = 0xe7  chan2 = 0xc0

000000: 01 00 a8 61  20 00 e7 00  0f 00 ff ff  0f 00 0f 00   |...a ...........|
000010: 00 00 32 00  00 00 01 00  0f 00 ff ff  ff ff c0 00   |..2.............|
000020: 2c 01 f6 ff  0f 00 e8 03  00 00 32 00  64 00 0a 00   |,.........2.d...|
000030: 0f 00 ff ff  ff ff

21 22 23 24 25  (telephone)
26
28

WARNING: Unimplemented PCjr chunk in sound 32:!
chan1 = 0x80  chan2 = 0xa0
000000: 01 00 40 1f  1c 00 80 00  32 00 0a 00  46 00 ee 02   |..@.....2...F...|
000010: f6 ff 46 00  ff ff fd ff  a0 00 ee 02  f6 ff 46 00   |..F...........F.|
000020: 32 00 0a 00  46 00 ff ff  fd ff 

WARNING: Unimplemented PCjr chunk in sound 33:!
chan1 = 0x80  chan2 = 0xa0
000000: 01 00 40 1f  1c 00 80 00  32 00 0a 00  46 00 ee 02   |..@.....2...F...|
000010: f6 ff 46 00  ff ff fd ff  a0 00 ee 02  f6 ff 46 00   |..F...........F.|
000020: 32 00 0a 00  46 00 ff ff  fd ff 

36

38 39 42 44 46
50
54 56 57 58
63 
70 71 72 73 74 75