MOD REPLAYING NOTES
Hipolito Carraro Jr. <hipolito@brhs.com.br>
Claudio Matsuoka <claudio@helllabs.org>
Last update: Sun May 16 13:43:42 EST 1999
1. Event fetch
Here is a list of several situations where Protracker, Fast Tracker II, Scream
Tracker 3 and Impulse Tracker behave differently due to the underlying event
handling algorithm used by these trackers.
xmp plays Protracker modules like Protracker 3.15 (marked as "standard" in
the tables). xCHN and xxCH play in FT2 style, S3M/STM/STX/PTM play in ST3
style.
Trackers compared:
PT1.1 = Protracker 1.1 (Amiga Freelancers, Dec 1990)
PT1.3 = Protracker 1.3 (Amiga Freelancers, May 1992)
PT2.3 = Protracker 2.3d (Mushroom Studios, Jan 1993)
PT3.15 = Protracker 3.15 (Cryptoburners, 1992-93)
PT3.61 = Protracker 3.61 (Design/RD10, 1996)
PT4b2 = Protracker 4.0 beta 2 (Thomas Beyer et al, Feb 1997)
MED = OctaMED Professional 4.0 (Teijo Kinnunen, 1992)
MTM = MultiTracker 1.01b (Daniel Goldstein, 1993)
FT2 = Fast Tracker II 2.06 (Triton (Starbreeze Studios), 1996)
ST3 = Scream Tracker 3.21 (Future Crew, 1994)
IO10 = Imago Orpheus 1.0 (Lutz Roeder, 1994)
IT(s) = Impulse Tracker 2.14, sample mode (Jeffrey Lim)
IT(i) = Impulse Tracker 2.14, instrument mode (Jeffrey Lim)
Protrackers downloaded from Aminet and Warlock's ADF archive and tested
with UAE 0.8.6 on Linux 2.1.130. Startrekker 1.2, Soundtracker 2.5 and
Noisetracker 1.0/1.2/2.0 don't run in this version of UAE (or at least I
couldn't make them run).
Behaviours:
Play = Play new note with new default volume
Trig = Play new note with old default volume
Switch = Play new note with current volume
LastSet = Play new note with last set volume
NewVol = Don't play sample, set new default volume
OldVol = Don't play sample, set old default volume
SetVol = Don't play sample, reset to last set volume
Cut = Stop playing sample
Cont = Continue playing sample
Case 1: New note
Instrument -> None Same Valid Inval
PT1.1 Play Play Play Cut
PT1.3 Play Play Play Cut
PT2.3 Switch Play Play Cut <=
PT3.15 Switch Play Play Cut <= "Standard"
PT3.61 Switch Play Play Cut <=
PT4b2 Switch Play Play Cut <=
MED Switch Play Play Cut <=
FT2 Switch Play Play Cut <=
ST3 Switch Play Play Switch
IT(s) Switch Play Play ?
IT(i) Switch Play Play Cont
Case 2: New instrument (no note)
Instrument -> None Same Valid Inval
PT1.1 - Play Play Cut
PT1.3 - NewVol NewVol* Cut
PT2.3 - NewVol NewVol* Cut
PT3.15 - NewVol NewVol Cut <= "Standard"
PT3.61 - NewVol NewVol Cut <=
PT4b2 - NewVol NewVol Cut <=
MED - Hold Hold Cut%
FT2 - OldVol OldVol OldVol
ST3 - NewVol NewVol Cont
IT(s) - NewVol NewVol Cont
IT(i) - NewVol# Play Cont
Case 3: Tone portamento
Instrument -> None Same Valid Inval
PT1.1 Cont NewVol?
PT1.3 Cont NewVol NewVol* Cut
PT2.3 Cont NewVol NewVol* Cut
PT3.15 Cont NewVol NewVol Cut <= "Standard"
PT3.61 Cont NewVol NewVol Cut <=
PT4b2 Cont NewVol NewVol Cut <=
MED Cont NewVol NewVol Cut <=
FT2 Cont OldVol OldVol OldVol
ST3 Cont NewVol NewVol Cont
IT(s) Cont NewVol NewVol Cont
IT(i) @ Cont NewVol NewVol Cont
# Don't reset envelope.
% Any valid instrument with no note is set as Hold. When the instrument
is invalid the channel is muted until the next valid instrument.
00 C-2 30000 <= Play instrument 3
01 | 30000 \
02 | 20000 > Continue playing instrument 3
03 | 10000 /
04 | A0000 <= Volume is set to 0 (instrument A is invalid)
05 | 40000 <= Continue instrument 3
* Protracker 1.3/2.3 switches to new sample in the line after the new
instrument event. The new instrument is not played from start (i.e. a
short transient sample may not be played). This behaviour is NOT
emulated by the current version of xmp.
00 C-2 03 A0F <= Play instrument 03 and slide volume down
01 --- 02 000 <= Set volume of instrument 02, playing instrument 03
02 --- 00 000 <= Switch to instrument 02 (weird!)
00 C-2 03 000 <= Play instrument 03
01 A-3 02 308 <= Start portamento with instrument 03
02 --- 00 xxx <= Switch to instrument 02 (weird!)
@ Tone portamento works in IT, instrument mode, only while the sample is
playing. After that, the tone portamento effect is ignored and the
new note is played.
00 C-2 01 000 <= Start instrument 01
01 --- 00 000
02 C#2 01 G0F <= Tone portamento effect works as expected
03 --- 00 000
04 --- 00 000 <= End of instrument 01
05 C-2 01 G0F <= Play instrument 01 again (yuck!)
2. XM and IT envelopes
When sustain loop is on, IT ignores the envelope loop. When the key is
released execution jumps from the current point inside the sustain loop
to the start of the envelope loop. XM envelope loops act like IT sustain
loops when the sustain point and the envelope end point are the same
(i.e. loop is active only while key is pressed). This behaviour is
correctly emulated by xmp.
3. Periods and replay rates
xmp plays Protracker and Fast Tracker II modules at standard PAL rate of
7093789.2 / (428 * 2) = 8287.137 for middle C. Scream Tracker III and Impulse
Tracker play with the NTSC rate of 7159090.5 / (428 * 2) = 8363.423. Using
MED BPM = 125/33 of Protracker BPMs, the Desert Strike MMD1 plays better
with NTSC replay rate. (Claudio's note: Does that mean that the correct tempo
for MED is _not_ 125/33 of the PAL vblank rate?)
4. Error in the Protracker 2.1 docs
The effect commands description in the Protracker 2.1A docs state that
effect E5x is used to set the loop start point and effect E6x is used
for loop jump. The player code shows that effect E5x is used for finetune
setting, E60 for loop set and E6x, x > 0, for loop jump.
PT.Effects_2.1a.txt:
...
E5- Set Loop E5x : set loop point
E6- Jump to Loop E6x : jump to loop, play x times
...
(Same description in Protracker V2.3A/3.01)
PT-Play_2.1a.s:
1 ;**************************************************
2 ;* ----- Protracker V2.1A Playroutine ----- *
3 ;* Peter "CRAYON" Hanning / Mushroom Studios 1992 *
4 ;* Vinterstigen 12, 14440 Ronninge, Sweden *
5 ;**************************************************
6
...
802 mt_E_Commands
803 MOVE.B n_cmdlo(A6),D0
804 AND.B #$F0,D0
805 LSR.B #4,D0
...
815 CMP.B #5,D0
816 BEQ mt_SetFineTune
817 CMP.B #6,D0
818 BEQ mt_JumpLoop
...
865 mt_JumpLoop
866 TST.B mt_counter
867 BNE mt_Return2
868 MOVE.B n_cmdlo(A6),D0
869 AND.B #$0F,D0
870 BEQ.S mt_SetLoop
871 TST.B n_loopcount(A6)
872 BEQ.S mt_jumpcnt
873 SUBQ.B #1,n_loopcount(A6)
874 BEQ mt_Return2
5. Pattern loops
Pattern loops are set by channel, and nesting is allowed as long as
the loops are in different tracks. The nested loop behaviour is somewhat
nonobvious as seen in the following examples.
00 --- 00 E60 | --- 00 E60 00 --- 00 000 | --- 00 E60
01 C-2 01 000 | --- 00 000 01 C-2 01 000 | --- 00 000
02 --- 00 E62 | --- 00 E62 02 --- 00 000 | --- 00 E62
In both cases the note is played three times.
00 --- 00 E60 | --- 00 E60
01 C-2 01 000 | --- 00 000
02 --- 00 E63 | --- 00 E62
In this situation the note is played twelve times. We escape the loop when
both counters are zeroed. Here's how the internal registers look like:
Iteration => 1 2 3 4 5 6 7 8 9 A B C
Channel 1 => 3 2 1 0 3 2 1 0 3 2 1 0
Channel 2 => 2 1 0 2 1 0 2 1 0 2 1 0
If a loop end is used with no start point set, it jumps to the first line
of the pattern. If a pattern break is inside a loop and there is a loop
end in the next pattern it jumps to the row set as loop start in the
previous pattern. It is also possible to make an infinite loop in
Protracker and Fast Tracker II using nested loops in the same track:
00 --- 00 E60 | --- 00 000
01 --- 00 000 | --- 00 000
02 C-2 01 000 | --- 00 000
03 --- 00 E61 | --- 00 000
04 --- 00 E61 | --- 00 000 <= infinite loop
S3M and IT set a new start point in the line after the end of the previous
loop, making the infinite loop impossible.
6. Effect 9 quirks
From: Martin Willers <y0000121@rzbcosv1.rz.tu-bs.de>
Subject: Incorrect Protrack-effect 0x09
To: xmp-bugs@helllabs.org
Date: Mon, 21 Dec 1998 05:28:48 +0100 (MET)
Reply-to: M.Willers@tu-bs.de
I've downloaded and installed the xmp-snapshot from Sun, Dec 20 today.
Don't know just how good the protrack-emulation is planned to get, but
there's a bug in the interpretation of Protracker's handling of effect 0x09
(SetSampleOffset), that causes some MODs to play incorrectly.
Original Protracker-source has some bug in handling effect 09, in that
the sample offset given in the effect byte is added +twice+ to the current
sample offset, once before playing this instrument (as is expected), and
once again after this instrument has been played! So, if on the same channel
the same instrument is played again without resetting the instrument's
parameters (eg. when just a note period is specified, but not the instrument
number again? or the other way round? :), the offset is twice as high
as one would expect.
This can be heard very easy eg. in the (very popular) song "No Mercy" by
Alf/VTL, Position #2-#3 in the sequence.
--
Date: Tue, 22 Dec 1998 23:57:48 -0200
From: Claudio Matsuoka <claudio@helllabs.org>
To: M.Willers@tu-bs.de
Subject: Re: Incorrect Protrack-effect 0x09
Ok, we played a bit with some custom-crafted mod to learn more about
effect 0x09. Here are the results:
Using the "OK" sample from ST-02
00 C-2 01 906 PT23 : kay - ay - ay - okay <= buggy
01 --- 00 000 PT315 : kay - kay - kay - okay
02 C-2 00 000 MED : kay - kay - kay - okay
03 --- 00 000 ST3 : kay - kay - kay - okay
04 C-2 00 000 IO10 : kay - kay - kay - okay
05 --- 00 000 MTM : kay - okay - okay - okay
06 C-2 01 000 FT2 : kay - okay - okay - okay
07 --- 00 000 IT : kay - okay - okay - okay
So it seems that the bug was fixed somewhere between Protracker 2.3d and
3.15. The problem is that there's no way to know if the bug emulation is
desirable or not when playing M.K. mods! I believe that mods _requiring_
this bug to be emulated are quite rare, so it will be switched using a
command line parameter or via xmp-modules.conf.
7. XM file format anomalies
The official XM file format description distributed with Fast Tracker II
says "The XM module format description for XM files version $0104" and
"The current format is version $0103". The format description and actual
modules made with the tracker differ in the reserved bytes at the end of
the instrument data (2 bytes in the description and 22 in 1.04 modules)
and the sample header size field: the document says that it belongs to the
sample header data, but in XM files created by Fast Tracker II it is in
the instrument. "Braintomb" by Jazztiz/ART (jz-btomb.xm) has this field
in the sample header data. "Braintomb" is marked as 1.04 and the tracker
name field is empty.
The instrument size field is 33 for XM files created with Fast Tracker II.
"Braintomb" has 29 in this field, because the sample header size is in
the sample header structure. Modules converted with MED2XM or created with
other trackers can have the size of instrument data plus the size of the
sample header data in this field. There is a version of "<unnamed>"
(Counterpoint 2.0, untitled.xm) with 245 in this field. In this module the
instrument type ("always 0" according to xm.txt) is 0xda. This module is
marked as 1.04 made with "FastTracker v 2.00". Note that authentic
FT2 modules are marked as "FastTracker v2.00".
Extended Module 1.02 (Vogue's "Trans atlantic" and "Dont you" remixes) and
1.03 (Vogue's "Developer 94" and "Enhanced Intuition") contains header,
instruments, patterns and samples in that order. 1.04 has header, patterns,
instruments and samples. XM 1.02 uses one byte to store the number of rows
in the pattern header, XM 1.03 and 1.04 use a 16-bit word.
8. Broken sample loops in converted MOD files
To play a sample using the 8364 Paula chip in Amiga, you must set a pointer
to the audio data in AUDxLCH (byte aligned) and the length in words in
AUDxLEN. Soundtracker uses the sample loop start in bytes and the length in
words, but Protracker uses both values in words. Some converters were not
aware of this feature and used the sample loop start in 16 bit words when
converting old Soundtracker modules to M.K., resulting in broken sample
loops. One example of broken converted M.K. mod is "Souvenir of China".
Other formats where offsets in words are hard to detect:
- GMC modules created with NoiseConverter have loop size / 2 .
- UNIC modules from "Guardian Dragon" have loop start / 2. Modules from
"Guardian Dragon II" have loop start / 4.
- NoisePacker v2 format is the same as NoisePacker v1 with loop start / 2.
9. Startrekker FLT8 format
Multichannel variations of the standard MOD (e.g. 8CHN) have channels stored
side by side. This is NOT the case of Startrekker. Here are Bjorn Wesen's
words about it (text written in Mar 1994):
"In regards of the Amiga StarTrekker format: It says FLT8 instead of FLT4 or
M.K., AND, the patterns are PAIRED. I thought this was the easiest 8 track
format possible, since it can be loaded in a normal 4 channel tracker if
you should want to rip sounds or patterns. So, in a 8 track FLT8 module,
patterns 00 and 01 is 'really' pattern 00. Patterns 02 and 03 together is
'really' pattern 01. Thats it. Oh well, I didnt have the time to implement
all effect commands either, so some FLT8 modules would play back badly (I
think especially the portamento command uses a different 'scale' than the
normal portamento command, that would be hard to patch)."
Uhm... I wonder what different scale is it.
10. Global volume setting
Effect V (global volume setting) in Scream Tracker 3.21 does not affect events
in the same line where the effect is set. Fast Tracker 2.06 global volume
affects the columns to the right of the column where the effect is set (weird!
-- could someone check this please?). Impulse Tracker 2.14 and Imago Orpheus
1.0 use global volume and slides as, well, global volume and slides (i.e.
affects all tracks).
00 B-3 21 000 | --- 00 000 ST3: plays only instrument 21
01 --- 00 000 | --- 00 G00 FT2: plays 21 and cuts 22 at row 03
02 B-3 22 000 | --- 00 G40 IT: cuts 21 at row 01 and 22 at row 03
03 --- 00 G00 | --- 00 000
Reference: Necros' "Mechanism Eight", pattern 93, channels 0 to 2, row 02.
11. Cut effect
When the cut effect is used with parameter 0 (cut after 0 frames) Protracker,
Fast Tracker and Impulse Tracker don't start to play the sample. Scream
Tracker and Imago Orpheus ignore the effect and don't cut the instrument.
Subsequent note events with no instrument set are not played in Protracker.
(must check in other trackers)
To check: cut effect with parameter > speed.
12. Imago Orpheus
Error in format specs:
The following differences have been found comparing Karsten Koch's IMF
files with the format specs for the Imago Orpheus file format version 1.00
written by Lutz Roeder:
- Channel status: 0x00 = channel disabled
- Envelope flags: 0 = off, 1 = on
Other IMF notes:
- Fine effects are 4 times finer than S3M extra fine effects
- Note values 160 (?) and 255 are key off events
- 'First effect' is the secondary effect
- In effect Mxx (0x16) xx = 0x00 is the highest cutoff frequency
- In effect Nxy (0x17) x = final cutoff value for slide, y = resonance
bit 7 = 0: Decrease cutoff frequency
bit 7 = 1: Increase cutoff frequency
bits 6-4: final cutoff frequency (0 = highest)
- Filter settings are not reset in new events!
12. Tracker tracking
Restart pos in M.K.:
0x7f = Protracker or clone (including ST3)
0x78 = ??? Possibly noisetracker
Restart pos = Noisetracker (or Fasttracker?)
Number of patterns = Soundtracker
Noisetracker, Protracker and ST3 set the default volume of unused instruments
to 0x40 and the default loop size to 0x0002. Fasttracker sets the default
volume to 0x00 and the default loop size to 0x0000.
S3M tracker codes:
1 = Scream Tracker 3
2 = Imago Orpheus
3 = Impulse Tracker
12. Misc effects
To check: (volunteers?)
- Keyoff events with instrument set
- Vibrato depth
- Funk repeat
