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?
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
Offset Length Type ? 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
Offset Length Type ? 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:
Offset Length Type ! +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
Offset Length Type ! ? 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;
The patterns are stored as ordinary MOD patterns, except that each note is stored as 5 bytes:
Offset Length Type ? 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.
FinalVol=(FadeOutVol/65536)*(EnvelopeVol/64)*(GlobalVol/64)*(Vol/64)*Scale;
FinalPan=Pan+(EnvelopePan-32)*(128-Abs(Pan-128))/32;
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.
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)
Period = 10*12*16*4 - Note*16*4 - FineTune/2; Frequency = 8363*2^((6*12*16*4 - Period) / (12*16*4));
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);
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.
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