Describe your idea
In the field of music, shifting pitch is about adding and subtracting the number of keys, not multipling. Multipling changes the interval while adding and subtracting (changing pitch) not. Here're two pics that might help explain:


As you can see, the red one (pitch=0.5) goes differently, which could make a song sounds terrible.
So, in short, use the same method of pitch shifter (highering/lowering keys) instead of using an index would be better.
Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
Idk.
Additional context
Here's the background. C418 songs are perfect for vanilla Minecraft, but might not suit well in a themed modpack, the rhythm, the content... there're so many differencies. I tried adding royalty free songs, but that's not enough, I got tired of them soon. So I came up with the idea of pitch-shifting system (two variations for each song), which can add more variation to the song list.

The pitch parameter currently does not work at all in the 6.x system, but I will keep this in mind for when I get to fixing it

I will be looking into this for 6.4