I've been using Nitro Studio for the past few weeks to make soundtracks for my hacks, and for some reason today it's been acting up. It was working fine and dandy until I reached the goal fanfare .sseq. I made a MIDI file for it, inserted it in, but for some reason the ending note would drag on loudly forever after the jingle had finished, despite the MIDI saying otherwise. I kept trying to fix it, but eventually I gave up and made a completely new jingle. Right after this, I had to work on the boss music. I used Newer's .sdat file as a base for the upgraded sound effects, though I wanted to use the original game's boss music. So I went to the original .sdat, extracted the boss music's files, and put them into the .sdat I was working on. But the same problem occurred with notes holding too long, though this time it was at the start and it was louder. Thinking I might have messed up extracting, I extracted and put the files in again. No luck. I was confused and started testing. I had made a .sseq before for the boss music's files for another hack, so I tested putting that .sseq in, which I knew for a fact worked before, but the same problem happened again. I've re-extracted the boss music's files many times now, I've even restarted my whole computer hoping it was just a one-time thing, but no.

The weirdest part is that when I go to the original game's .sdat and insert the malfunctioning music files, it works fine, but the moment I enter it into a new .sdat, it acts up. I would like to know if anyone knows what's going on and if there's a way to fix it.
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Check out "New-ISH" Super Mario Bros. DS HD*!!
Renewed Super Mario Bros. still exists, though.

try using smfconv and seqconv (sdk tools) to convert to sseq instead of midi2sseq (what nitro studio uses). they tend to work better.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

I can't seem to find what you're talking about. Could you provide a link to one of the two?
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Check out "New-ISH" Super Mario Bros. DS HD*!!
Renewed Super Mario Bros. still exists, though.

No he cannot. Those files are part of the SDK and that is as forbidden as sharing ROMs.
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GitHub - Kuribo64 - YouTube

also, you need both of them. smfconv to convert the midi to smft and seqconv to convert the smft to sseq.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

Would Nintendo still care at this point about tools from the SDK being shared though?

probably not, but better safe than sorry
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.