'===========================================================================
' Subject: 669 FILE FORMAT                    Date: Unknown Date (00:00)   
'  Author: Unknown Author(s)                  Code: TEXT                   
'  Origin: 669,FORMAT                       Packet: SOUND.ABC
'===========================================================================
      Here's the file format for 669s. They are much like MODs, but they
have 8 tracks in them and the samples are unsigned. That unsigned part
has been causing trouble for people trying to rip samples from MODs and
using them in 669s. To fix a sample, just XOR every byte in it with 128.
This will flip the signed bit, making everything right...

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.669 file format:

offset         +length&type    +description
---------------+---------------+---------------------------------------
------
0              |1 word         |marker, value=0x6669
2              |108 bytes      |song message
0x6e           |1 byte         |NOS = number of samples saved (0-64)
0x6f           |1 byte         |NOP = number of patterns saved (0-128)
0x70           |1 byte         |loop order number
0x71           |0x80 bytes     |order list
0xf1           |0x80 bytes     |tempo list for patterns
0x171          |0x80 bytes     |break location list for patterns
0x1f1          |NOS*size struct|sample data
               | samp          |
+--------------+---------------+
|struct samp {
|  13 bytes ASCIIZ filename of instrument
|  1 dword length of instrument
|  1 dword offset of beginning of loop
|  1 dword offset of end of loop
|} smp[NOS]
+--------------+---------------+---------------------------------------

0x1f1+         |NOP*0x600      |patterns
(NOS*0x19)     |               |
+--------------+---------------+
|this is repeated 8 times for every row and the array of 8 of these is
| repeated 64 times for each pattern.
|
| bits:
|   BYTE[0]:             BYTE[1]:            BYTE[2]:
|  aaaaaaaa             bbbbbbbb            cccccccc
|  |----Ù|-----------------Ù|--Ù            |--Ù|--Ù
|  |     |                  |               |   |
|  |     |                  4 bit volume    |   command value
|  |     |                                  |
|  |     aabbbb = 6 bit instrument number   command:
|  |                                         0 = a
|  note value = (12*oct)+note                1 = b
|                                            2 = c
|  special values for byte 0:                3 = d
|    0xfe = no note, only volume change      4 = e
|    0xff = no note or volume change         5 = f
|
|                                           special value for byte 2:
|                                             0xff = no command
|
+--------------+---------------+---------------------------------------

0x1f1+         |rest of file   |samples
(NOS*0x19)+    |               |
(NOP*0x600)    |               |

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