Broken IT modules

[m4tustechna]

Hello!

First of all, thank you for continuing to develop this awesome tracker. Your player was one of the main reasons I switched to GNU/Linux (before then, there weren't Windows builds).

I noticed that some tunes don't play well in OCP. I'm guessing that some IT files were probably converted from MO3. Both Future Crew and Skaven uploaded MO3 and IT versions, but I'm not sure.

All of these files played fine in Impulse, Schism, ModPlug, and OpenMPT.

I also noticed that MOD files run slightly slower than on the original Amiga hardware. I have to press CTRL+F11 to change the speed value by 0.33% instead of 3%. Then, I press F10 twice to reach 100.66% speed. This also happens on FastTracker ][.

Here are links to the files that play incorrectly:

Amazonas - Dynomite Mix (amazonas-1347.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=172351

Ocean Paradise (bacter_vs_saga_musix_-_ocean_paradise.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=193037

Beyond the Network (beyond_the_network.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=156184

Bookworm (bookworm.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=191058

Codename Silver (Codename_Silver.it)
http://www.futurecrew.com/skaven/song_files/Codename_Silver.it

Deep in her Eyes (deep_in_her_eyes_-_remake.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=133609

Fourth Symmetriad (skaven-fourth_symmetriad.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=67203

Hamster Ball (hamsterball_gold.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=179543

Rama Gardens v1.1 (rama_gardens_-_remake.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=133610

Bad Tracker!! (badapple.it)
https://modarchive.org/index.php?request=view_by_moduleid&query=179366

[mywave82]

Let me first comment on your remark regarding speed. That Open Cubic Player matches Fast Tracker II. It actually a good thing, since most of the Amiga formats are played back using "playxm", which is the Fast Tracker II playback driver.

playgmd
669 (Composer 669, DOS)
AMS (Extreme Tracker, DOS)
DMF (d-lusion X-Tracker, DOS)
MDL (DigiTrakker, DOS)
MTM (Multi Tracker by DigiTrakker, DOS)
OKT (Oktalyzer, Amiga)
PTM (Polytracker, DOS)
S3M (Scream Tracker 3, DOS)
STM (Scream Tracker II, DOS)
ULT (UltraTracker, DOS)

playit
IT (Impulse Tracker, DOS)

playxm
M15 (Noise Tracker 15 instruments, Amiga)
M15t (Noise Tracker 15 + ProTracker 1.1b tempo commands, Amiga)
M31 (Noise Tracker 31 instruments, Amiga)
MOD (ProTracker 1.1b, Amiga, ish)
MODd (ProTracker 1.1b + Dual Module Player panning, Amiga)
MODf (Fast Tracker II, DOS)
MODt (ProTracker 1.1b, only tempo, no speed, Amiga)
MXM (MXMPlayer, originaly XM files, DOS)
WOW (Mod's Grave utility, originally Composer 669 files, DOS)
XM (Fast Tracker II, DOS)

On PC, the playback can calculate exactly how many samples one tick should be.

On Amiga this work is put onto timers and interrupts, and to my knowledge, those timers had a given granularity that always would make the timers inaccurate. So if we want to Amiga compatibility an option, we likely need a lookup table, resolving module BPM values into real herz. Also PAL and NTSC Amiga have different base-clocks.

[mywave82]

I am looking at one detail at a time. So the timing is the first thing I am looking into.

Testing the algorithm from https://github.com/8bitbubsy/pt2-clone/blob/master/src/pt2_replayer.c vs calculating perfect BPM to tick lengths, the difference I get for a PAL Amiga is that speed should be set to 100.003% to match.

So that would not account for what you experience, the need for speed to be set to 100.66%.

How did you actually reach this number, and how does https://github.com/8bitbubsy/pt2-clone compare to your experience of what the correct speed should be.

I need to clarify what the cause is, before hunting this down any further,

[mywave82]

I believe ddefb1f fixes the broken IT files. Please verify if possible.

[m4tustechna]

I apologize for the delay in getting back to you.

How did you actually reach this number

I based it on OCP’s top-right speed value and counted how many times I pressed the F10 key. I’ll try to get the actual value you’re asking for sometime this week.

I believe ddefb1f fixes the broken IT files. Please verify if possible.

Playback does sound much more listenable now! Some of the samples are still a bit off, but honestly, I’m not complaining—I’m very happy with the results so far. Thanks a lot for taking the time to fix this!

[mywave82]

I am working on playback of stereosamples in actual stereo, and not downmixed to mono and panned. It works when testing, but I need to refine the code first