Why won't you look at the way BGT does it? It will at least give you an idea of how it is done. Regarding memory leaks, I have no sympathy for you, it is your choice to continue working in this language after all. All I can say is welcome to the joys of lower-level stuff.

yeah, there is a reason I go out of my way to warn people off this.  It's C with a weird syntax, but you don't have (say) address sanitizer to help you along with your manual memory management woes.  To do it right you need to manually implement and properly call destructors, that is (in C):

void foo_destroy(struct foo *what) {
    if (foo == NULL) return;
    /// freeing logic here, call whatever you have to for all the fields, then:
    free(what);
}

Then you have to make sure that these get called in all the right places.  It checks to see if the input object is NULL so that you can unconditionally call it.  You set all the variables that might be pointers to NULL, then modify all your functions to only return in one place wherever possible (C does this with goto, which is one of the only good uses), then whether or not the variable is null determines whether or not the destroy function does anything.  This requires a large amount of discipline.  In C you can check your work with address sanitizer and things like clang-analyzer; in Purebasic you have nothing to help you.  I know people who make me look like a junior whose entire career has been C and they still get this wrong, which isn't a huge deal because the aforementioned tools will catch it--but you don't have the aforementioned tools.  So good luck, and welcome to the world in which you understand that Purebasic manages to even be worse than C/C++.

But seriously, if you have been trying to get a sound pool working for years it probably would have taken you less time to just go rewrite the project.  Learn to give up and start over.

@6, PB already provides that in its bloated stdlib

If you want to "implement" Synthizer as in use another sound library and put a convenient API on top of it, in theory, but you've already tried and failed, so the answer for you is no.  Whether it's possible doesn't matter; whether it's possible for you does.  You could keep banging your head against Purebasic's inadequacies for a long time hoping you eventually get it, but Purebasic is a C variant and that's not how learning C variants work.  It's not worth the effort for you to step back and go learn programming in a disciplined manner, probably by finding books on C/C++, so that you can use Purebasicn effectively enough to finish this project.

At the end of the day C-like languages with manual memory management aren't compatible with the way that you and the rest of this community code where you start programming and immediately try for a project.  To use them, you have to spend at least 6 months more time than you'd have to spend on (say) Python, and if those 6 months aren't spent seriously studying resources on how to make reliable software or coding every single day, you won't manage it.  It took 2 or 3 years for me to achieve competency in C/C++, and I still make mistakes that things like address sanitizer and proper debuggers have to help me catch--and Purebasic doesn't have those tools, so when you fail, and you will, nothing can help you find out how.

Everyone looks back on PB fondly, but I remember 5 years ago or so when basically every game anyone put out was either that or BGT and you'd have huge threads on the PB one where the author was just continuously fixing bugs like these.

You guys think PureBasic is weird... Have you looked at BBC BASIC source code? I'm sorry, but that derivative should've died in the 80's, and trying to add modern features to it just makes the language even weirder.