I don't understand something here. Are you cutting a new opening in an existing wall between your studio and a hallway? If so, where is the door to the studio now? Can you post a drawing of this studio and hallway, showing where you want to put the door and where the existing door is. If this is a standard framed house, and there is enough room, it should be quite easy. And btw, forget the bifold door. You can't seal a bifold and they have no mass.
As to the door itself, if you can cut the opening big enough to frame it for a SOLID CORE door, which is much heavier than a standard hollow core interior door and requires a more robust framing, then do so. You can purchase a solid core door premounted on hinges/jamb fairly cheap. Since its an interior space, you can probably get away with a 30-32". Make your framed opening 2" wider than the door itself, which will allow the jamb and 1/4" on each side for shims.
Make the opening height 1-2" higher than the door itself, but possably higher, as you will have to allow for a threshold/seal as well, which you need to purchase at the same time to know how to allow for this thickness when framing.
But let me add a couple of caveats here. I don't know the conditions of the spaces you are trying to isolate from each other, but there is an isolation caveat that states any time you modify a space or wall/cieling/floor and or door to improve the transmission loss, your solution is ONLY as good as the "weakest link". In effect, this means that should you do this project, it may NOT improve anything, as existing wall/cieling/floor/HVAC conditions may be have a weaker transmission loss factor than the assembly you are adding. Which means, you may be wasting your time and money putting in a solid core door. Without knowing ALL the existing conditions/construction and your potential SPL of the music, a hollow core door may be the way to go, as it might be a waste to install a solid core door.
Secondly, since this is not your house, without permission to do this, you may jeaprodise your rental agreement, if not downright be a precurser to evicrtion and or repair costs

But thats up to you.
fitZ