Preview
The XM module format description for XM files version $0104.
By Mr.H of Triton in 1994.
- Be prepared! Are you sure you want to know? :-)
============================================================================
******************************
* The XM file structure: *
******************************
Offset Length Type
0 17 (char) ID text: 'Extended module: '
17 20 (char) Module name, padded with zeroes
37 1 (char) $1a
38 20 (char) Tracker name
58 2 (word) Version number, hi-byte major and low-byte minor
The current format is version $0103
60 4 (dword) Header size
+4 2 (word) Song length (in patten order table)
+6 2 (word) Restart position
+8 2 (word) Number of channels (2,4,6,8,10,...,32)
+10 2 (word) Number of patterns (max 256)
+12 2 (word) Number of instruments (max 128)
+14 2 (word) Flags: bit 0: 0 = Amiga frequency table (see below);
1 = Linear frequency table
+16 2 (word) Default tempo
+18 2 (word) Default BPM
+20 256 (byte) Pattern order table
Patterns:
---------
? 4 (dword) Pattern header length
+4 1 (byte) Packing type (always 0)
+5 2 (word) Number of rows in pattern (1..256)
+7 2 (word) Packed patterndata size
? ? Packed pattern data
Instruments:
------------
? 4 (dword) Instrument size
+4 22 (char) Instrument name
+26 1 (byte) Instrument type (always 0)
+27 2 (word) Number of samples in instrument
If the number of samples > 0, then the this will follow:
! +29 4 (dword) Sample header size
! +33 96 (byte) Sample number for all notes
! +129 48 (byte) Points for volume envelope
! +177 48 (byte) Points for panning envelope
! +225 1 (byte) Number of volume points
! +226 1 (byte) Number of panning points
! +227 1 (byte) Volume sustain point
! +228 1 (byte) Volume loop start point
! +229 1 (byte) Volume loop end point
! +230 1 (byte) Panning sustain point
! +231 1 (byte) Panning loop start point
! +232 1 (byte) Panning loop end point
! +233 1 (byte) Volume type: bit 0: On; 1: Sustain; 2: Loop
! +234 1 (byte) Panning type: bit 0: On; 1: Sustain; 2: Loop
! +235 1 (byte) Vibrato type
! +236 1 (byte) Vibrato sweep
! +237 1 (byte) Vibrato depth
! +238 1 (byte) Vibrato rate
! +239 2 (word) Volume fadeout
! +241 2 (word) Reserved
!
! Sample headers:
! ---------------
!
! ? 4 (dword) Sample length
! +4 4 (dword) Sample loop start
! +8 4 (dword) Sample loop length
! +12 1 (byte) Volume
! +13 1 (byte) Finetune (signed byte -16..+15)
! +14 1 (byte) Type: Bit 0-1: 0 = No loop, 1 = Forward loop,
! 2 = Ping-pong loop;
! 4: 16-bit sampledata
! +15 1 (byte) Panning (0-255)
! +16 1 (byte) Relative note number (signed byte)
! +17 1 (byte) Reserved
! +18 22 (char) Sample name
!
! Sample data:
! ------------
!
! ? ? Sample data (signed): The samples are stored
! as delta values. To convert to real data:
!
! old=0;
! for i=1 to len
! new=sample[i]+old;
! sample[i]=new;
! old=new;
***********************
* Pattern format: *
***********************
The patterns are stored as ordinary MOD patterns, except that each
note is stored as 5 bytes:
? 1 (byte) Note (0-71, 0 = C-0)
+1 1 (byte) Instrument (0-128)
+2 1 (byte) Volume column byte (see below)
+3 1 (byte) Effect type
+4 1 (byte) Effect parameter
A simle packing scheme is also adopted, so that the patterns not become
TOO large: Since the MSB in the note value is never used, if is used for
the compression. If the bit is set, then the other bits are interpreted
as follows:
bit 0 set: Note follows
1 set: Instrument follows
2 set: Volume column byte follows
3 set: Effect type follows
4 set: Guess what!
It is very simple, but far from optimal. If you want a better,
you can always repack the patterns in your loader.
******************************
* Volumes and envelopes: *
******************************
The volume formula:
FinalVol=(FadeOutVol/65536)*(EnvelopeVol/64)*(GlobalVol/64)*(Vol/64)*Scale;
The panning formula:
FinalPan=Pan+(EnvelopePan-32)*(128-Abs(Pan-128))/32;
Envelope:
---------
The envelopes are processed once per frame, instead of every frame where
no new notes are read. This is also true for the instrument vibrato and
the fadeout. Since I am so lazy and the tracker is rather self-explaining
I am not going to write any more for the moment.
********************************
* Periods and frequencies: *
********************************
PatternNote = 0..95 (0 = C-0, 95 = B-7)
FineTune = -128..+127 (-128 = -1 halftone, +127 = +127/128 halftones)
RelativeTone = -96..95 (0 => C-4 = C-4)
RealNote = PatternNote + RelativeTone; (0..118, 0 = C-0, 118 = A#9)
Linear frequence table:
-----------------------
Period = 10*12*16*4 - Note*16*4 - FineTune/2;
Frequency = 8363*2^((6*12*16*4 - Period) / (12*16*4));
Amiga frequence table:
----------------------
Period = (PeriodTab[(Note MOD 12)*8 + FineTune/16]*(1-Frac(FineTune/16)) +
PeriodTab[(Note MOD 12)*8 + FineTune/16]*(Frac(FineTune/16)))
*16/2^(Note DIV 12);
(The period is interpolated for finer finetune values)
Frequency = 8363*1712/Period;
PeriodTab = Array[0..12*8-1] of Word = (
907,900,894,887,881,875,868,862,856,850,844,838,832,826,820,814,
808,802,796,791,785,779,774,768,762,757,752,746,741,736,730,725,
720,715,709,704,699,694,689,684,678,675,670,665,660,655,651,646,
640,636,632,628,623,619,614,610,604,601,597,592,588,584,580,575,
570,567,563,559,555,551,547,543,538,535,532,528,524,520,516,513,
508,505,502,498,494,491,487,484,480,477,474,470,467,463,460,457);
*************************
* Standard effects: *
*************************
0 Appregio
1 (*) Porta up
2 (*) Porta down
3 (*) Tone porta
4 (*) Vibrato
5 (*) Tone porta+Volume slide
6 (*) Vibrato+Volume slide
7 (*) Tremolo
8 Set panning
9 Sample offset
A (*) Volume slide
B Position jump
C Set volume
D Pattern break
E1 (*) Fine porta up
E2 (*) Fine porta down
E3 Set gliss control
E4 Set vibrato control
E5 Set finetune
E6 Set loop begin/loop
E7 Set tremolo control
E9 Retrig note
EA (*) Fine volume slide up
EB (*) Fine volume slide down
EC Note cut
ED Note delay
EE Pattern delay
F Set tempo/BPM
G Set global volume
H (*) Global volume slide
K Key off
L Set envelope position
P (*) Panning slide
R (*) Multi retrig note
T Tremor
X1 (*) Extra fine porta up
X2 (*) Extra fine porta down
(*) = If the command byte is zero, the last nonzero byte for the
command should be used.
*********************************
* Effects in volume column: *
*********************************
All effects in the volume column should work as the standard effects.
The volume column is interpreted before the standard effects, so
some standard effects may override volume column effects.
Value Meaning
0 Do nothing
$10-$50 Set volume Value-$10
: : :
: : :
$60-$6f Volume slide down
$70-$7f Volume slide up
$80-$8f Fine volume slide down
$90-$9f Fine volume slide up
$a0-$af Set vibrato speed
$b0-$bf Vibrato
$c0-$cf Set panning
$d0-$df Panning slide left
$e0-$ef Panning slide right
$f0-$ff Tone porta
============================================================================
This should be just about everything (I hope?). You will probably need
some information about the MOD format and maybe about S3M.
Have fun!
Fredrik Huss / Mr.H of Triton