xmp/doc/format/digi_format
analysed by Claudio Matsuoka <claudio@helllabs.org>
Sun Feb 21 18:20:32 EST 1999

Format: DIGI
Version: 1.6
Author: Tomasz and Waldemar Piasta
Tracker: DIGI Booster (Amiga)

DIGIBooster is an 8 channel tracker written in Poland by Tap & Walt/INV.
The format description below is based on the DIGI Booster v1.6 replayer
written by Tomasz Piasta in June, 1996 and tested with several modules
available at Aminet. Byte order is big endian. Thanks to Louise Heimann
for the help with decoding.

Note: this description is unchecked and not complete -- information about
unpacked patterns and PackEnable bytes in header are missing.

DIGI module header:

Offset	Size	Description
------- ------- --------------------------------------------
     0      20  Format ID: "DIGI Booster module\0"
    20       4  Version string: "V1.6"
    24	     1	Version: 0x16
    25       1  Number of channels (up to 8)
    26       ?  PackEnable
    46	     1	Number of patterns - 1
    47	     1	Number of orders - 1
    48	   128	Orders
   176	  31*4	Sample length (for 31 samples)
   300	  31*4	Sample loop start (for 31 samples)
   424	  31*4	Sample loop length (for 31 samples)
   548	  31*1	Sample volumes (for 31 samples)
   579	  31*1	Sample finetunes (for 31 samples)
   610	    32	Song name
   642	 31*30	Sample names (for 31 samples)
  1572	     ?	Song data


DIGI packed patterns:

Offset	Size	Description
------- ------- --------------------------------------------
     0	     2	Size of the pattern data (PS)
     2	    64	Bit masks for events in this pattern (see below)
    66	 PS-64  Pattern data

There are 64 bit masks for each pattern. If a bit in the bit maks is set
it means that an event in that channel should be read. Events are encoded
as in Protracker:

        period value
       /           \
      |             |
 0000 0000  0000 0000  0000 0000  0000 0000
 |  |                  |  | |  |  |       |
  \  \                /  /   \/    \     /
   `----Sample number---'  effect   effect
                                   parameter

Protracker periods:

C-1 to B-1 : 856,808,762,720,678,640,604,570,538,508,480,453
C-2 to B-2 : 428,404,381,360,339,320,302,285,269,254,240,226
C-3 to B-3 : 214,202,190,180,170,160,151,143,135,127,120,113


DIGI effects:

    0xx  Arpeggio
    1xx  Portamento up
    2xx  Portamento down
    3xx  Tone portamento
    4xy  Vibrato
    5xx  Tone portamento + volume slide
    6xx  Vibrato + volume slide
    7xx  Tremolo (not implemented in 1.6)
    8xx  Robot ("metallic" effect on sample) - 800 uses previous value
    9xx  Sample offset
    Axy  Volume slide
    Bxx  Pattern jump
    Cxx  Set volume
    Dxx  Pattern break
    Exx  Extended effect (see below)
    Fxx  Set speed

    Extended effects:

    E00  Filter off
    E01  Filter on
    E1x  Fine slide up
    E2x  Fine slide down
    E3x  Play sample backwards
	 x=0 "plays sample from backward" (sic)
	 x=1 "plays sample from backward, next from front loops" (sic)
    E40  Stop playing sample (apparently this effect exists for performance
	 reasons)
    E6x  Pattern loop
    E8x  0xffff*x sample offset
    E9x  Retrace (?)
    EAx  Fine volume up
    EBx  Fine volume down
    ECx  Cut sample
    EDx  Sample delay
    EEx  Pattern delay


DIGI samples:

Stored like Protracker. Sample size is not limited to 64 Kb.

