If they're playing music... forget it, no sleep for me.
This is almost certainly the one thing that you can do A LOT about at very little cost.
To be honest with you, I wish you would read the paper by Mr. Quirt of the Canadian National Research Council on reducing noise transmission through building components like walls, floors, ceilings, windows and doors.
Sound Transmission Through Building Components - NRC-CNRC
That will convince you that the noise reduction you're likely to get by blowing cellulose insulation into your ceiling joist space is gonna be a disappointing waste of money. There are two reasons for this:
1. The first one is that adding sound absorbing materials like insulation to a wall, floor or ceiling is pretty well a waste of time and money if there are studs or floor joists that connect the two sides of the wall, floor or ceiling. That's cuz any movement of one side of the wall or floor is going to result in the simultaneous and equal amount of movement on the other side of the wall or ceiling, so any sound wave hitting the wall or floor is going to be accurately reproduced by the other side of that wall or ceiling. Sound absorbing materials are only helpful when you don't have any mechanical linkage between your wall and your neighbors, or your ceiling and your neighbor's floor. You can do that by building two walls, or using a 2X6 as the bottom and top plates, and staggering the 2X4 studs so that half of them support the drywall on one side and the other half support the drywall on the other.
2. And the second reason why is that sound is a pressure wave in the air and behaves all the laws of physics just like any other wave does. It's the fact that sound is a wave that allows me to explain in simple terms why the cellulose insulation in the ceiling won't do very much good.
When a sound wave hits a wall, floor or ceiling what happens is that the wall, floor or ceiling moves in response to the changing pressure on one side of it. It is that movement of the wall, floor or ceiling that reproduces another sound wave on the other side of the wall, floor or ceiling. It is this second "reproduced" sound wave that that we hear, NOT the original.
And, I can prove that by showing how the Mass Law results in our hearing only a "BOOM-BOOM-BOOM" and not all of the music when someone is having a party late at night in the same building we're living in.
The "Mass Law" is one of the basic principles of accoustics. The Mass Law says that for every:
a) doubling of the mass per given area of the wall, floor or ceiling, or
b) doubling of the frequency of the sound waves hitting the wall, floor or ceiling, then
the sound pressure level of the "reproduced" sound wave on the other side of the wall, floor or ceiling will be reduced to 1/4 of it's initial value, or by 6 decibels.
And the reason why is that by doubling the mass of the wall, you also double it's inertia. When you do that, the wall simply doesn't move as fast or as far under the same applied force. The smaller and slower movement of the wall means that the reproduced sound wave is lower in amplitude, which our ears recognize as being "quieter".
Similarily, if you double the frequency of the sound waves hitting the wall, then the inertia of your existing wall makes it progressively harder and harder for your wall to change it's direction of movement fast enough to respond to the sound waves hitting it. Once the frequency is high enough that the inertia of the wall prevents it from moving in response to those sound waves, the wall simply stops moving in response to those sound waves, and that means the wall stops moving. Unless something else is making noise on the other side of the wall, it's quiet on the other side of the wall.
It is these simple principles of physics that explain why you hear BOOM-BOOM-BOOM when there's a party going on in your building late at night. What's happening is the midrange and treble frequencies are too high for the walls and ceilings to respond to, so you don't hear them. The only frequencies that are low enough for the walls and ceilings to respond to are the deep bass frequencies. Consequently, your walls and ceilings only move in respond to those low frequencies, and that's the only sound that is reproduced by the walls, floors and ceilings. This is why you only hear BOOM-BOOM-BOOM when they're playing a song you know well. You have to get close enough to the source of the sound so that there are no walls, floors or ceilings between you before you will hear the midrange and trebel and recognize the music being played.
OK, so if you blow this cellulose insulation into the space between the ceiling joists, the amount it's going to help is going to be directly proportional to the amount it increases the mass per square foot of what's there now. It's only going to help significantly if your neighbor's wall wasn't mechanically connected to your ceiling by the joists. That's because the joists connect both sides of the floor structure, and so movement of the neighbor's floor is going to result in exactly the same movement of your ceiling. So, you can consider the entire floor/joist/ceiling a single "wall" of uniform composition and density and apply the Mass Law. You can do a rough calculation on your own. You know wood floats, so it's density has to be less than that of water. 0.8 say. It shouldn't be hard to find out how much a 1/2 inch by 32 square foot sheet of drywall weights and you know the area of your ceiling (roughly). And, you can probably assume 2X12 fir joists on 16 inch centers. Now add to that 12 inches (say) of cellulose insulation at, what, 3 or 4 pounds per cubic foot say (?) to see how much of a percent difference you're gonna make in the mass of that "wall" over your head.
Here's my best advice:
1. Deal with the stereo first: Explain what I've explained to you to your neighbor, and make him an offer: You'll buy him a set of good quality ear phones (which he will return when either of you move) if he will agree to turn the bass control on his stereo (or music source) all the way down when he's not using the ear phones. Since the source of the low frequency sound is the movement of the walls and floors in response to the low frequeincy sound created by the woofers, by stopping the movement of the woofers, we eliminate the bass frequencies which cause the "BOOM-BOOM-BOOM" you hear in your condo.
2. Deal with the foot steps next: Make your upstairs neighbor another offer: If he installs carpet in his apartment, you'll go halfers on a thicker and better quality underpad to go under it. (I know this is killing you.) The reason why the footsteps are loud is because the whole floor/joist/ceiling structure moves in response to 175 pounds suddenly coming down on it in one spot and causing it to vibrate. That's called "impact loading". By having a thick underpad under the carpet, you slow the rate at which that load is applied to the floor, (cuz underpad foam rubber is a lot softer than shoe heel rubber so it compresses more over a longer period of time) and that slows the movement of the floor/joist/ceiling in response to footsteps. If the movement of your ceiling is slower, then the sound pressure wave created when it moves is weaker (which means that the air pressure doesn't change as much as fast), and that translates into "quieter" noise.
The problem, of course, is that he might not want to give up his hardwood floor.
I'd look up "Engineers, Accoustical" in your yellow pages and phone one of them up. Explain what you've learned from posting online and reading various papers and see if he agrees that the earphones/underpad will be both more effective and considerably less expensive than the insulating idea.
There are noise and vibration isolation devices but to retrofit a building with these, even around one condo is likely going to be cost prohibitive.
Also, you already know that increasing the MASS of your floor/joist/ceiling structure is the single biggest factor in determining how much noise comes through. So, spending $5000 to REPLACE the drywall on the ceiling with Quietrock (whatever that is) is likely to be less effective than spending $3000 to ADD a second layer of ordinary drywall to your existing ceiling. Obviously, your drywall contractor doesn't know much about accoustics.
Click on the link above and read through it before making any decisions.
(Aside: Also remember that our hearing isn't linear. We hear quiet sounds much better than louder ones. So, a 25% (or 6 dB) reduction in the sound pressure level won't seem to be only one quarter as loud as it was before. You'd probably perceive a 6 dB drop in the noise level to be "half as loud" as before (at best).)
PS: The Canadian National Research Council is a government funded research group that does research into problems pertinant to Canadians and the Canadian climate. They do a lot of research on insulation and energy savings. You can access all of the information available from the Canadian National Research Council on their web site at:
Then left click on Library and Publications
Then left click on NRC Publications
Then click on Browse by Subject
You should be able to find the paper by J. A. Quirt under the heading "Construction", but it may take a while since the NRC has issued 16,488 publications under that general heading. (Best to use the "Advanced Search" feature and type in part of the title.)
In case you hadn't thought of it, the NRC web site is an excellent tool to research just about any subject; as is Google itself.