The best answer is to save your money and not treat the walls. You could have the most impressive soundproof walls in the world, but you will not see their value with a standard dropped ceiling.
A dropped (suspended) ceiling does very little to soundproof. The tiles are lightweight and not nearly massive enough to stop serious sound. Basically, the tiles are not designed to be soundproof, they are designed to lower the echo underneath them. So the person in the office cubicle next to you can’t hear you as clearly, even though they can hear your voice. The tiles are also not sealed, as they lie loosely in a lightweight track. We explain how it works in our article entitled The 4 Elements of Soundproofing.
If you have the height to spare, though, there are options. One is to drop the framing down 2” or so, and then attach drywall. This will align the ceiling drywall in a way that allows you to run the drywall all the way down and seal the drywall to the foundation. You lose ceiling height, but effectively put a lid on the room.
The other option is to keep the ceiling height, but build decoupled walls. This is covered in depth here: Building a Room Within a Room