Let me know if you have any specific questions, OP. This is my bread and butter.
Love to hear your thoughts on ceiling soundproofing and soundproofing in general, if you have time sometime to type out a long(er) post. We bought a house a couple years ago that has siding only (all prior houses have been brick or double brick). Siding is shitty at blocking sound from the houses on both sides.
I've done a fair bit of reading on the subject. We're having the siding replaced this coming year (it is 30+ years old and done) and thinking about going with a cement board product (like Hardie) for looks and sound attenuation. On the inside, I'm only really interested in soundproofing our bedroom so will likely add a second layer of drywall with perhaps acoustic insulation in between. However, like the OP, we have no idea what to do with the ceiling (and realize that it is pointless to soundproof the walls and not do the ceiling as well).
It's great to hear that you're thinking of this factor now before starting your projects; one of the biggest problems I've observed is that most people don't think about noise before their project is designed/built and then have an issue that is much more difficult to treat after the fact.
If you're a more technical kind of person and want all of the nitty gritty details regarding some lab data related to your siding project, then this Canadian research report is the most comprehensive document that is freely available that I'm aware of:
http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=b516cfdd-0170-4427-9532-77daf90974d5Regarding some of the overly technical stuff: STC (Sound Transmission Class) and OITC (Outdoor-Indoor Transmission Class, same as STC just includes lower frequencies in the range of what a subwoofer produces) are single number laboratory ratings that characterize the ability of a wall/partition to reduce the transmission of airborne sound. A higher number is better in both cases and loosely estimates the amount that noise is reduced by a wall. For example, a high performing wall with an STC of 50 would reduce a noise of 80 dB (quite loud) on one side to approximately 30 dB (perceived as pretty darn quiet) on the other.
If you don't want to look at that report, then hey, I don't really blame you - it's kind of dry :) What it comes down to is that you will want
mass to help increase sound attenuation for a building facade, especially at lower frequencies. Think of a motorcycle driving past your house in the middle of the night - you don't want to hear that! So that's why brick or a cement board product is effective - because it's heavier than a lot of alternatives like vinyl. That's why thicker (Type C or X) or extra layers of drywall are commonly recommended as well for interior spaces. You'll also see that fenestrations, such as windows and doors, will be the weakest spots of the composite wall. Sound is a lot like heat or water in that it will take the path of least resistance to leak through to the other side. If electrical, plumbing, etc. penetrations aren't properly sealed then the wall's performance can be severely degraded, even with gaps that appear pretty small to the eye. Details matter!
Some other thoughts that are more or less unrelated to your siding project:
1. I already mentioned that mass helps attenuate airborne sound, especially at low frequencies. The other big factor when it comes to sound transmission is "stiffness", which pretty much boils down to how much internal damping a wall has; which is to say how well will it transmit vibrations through the wall assembly (from the drywall to the studs and out the other side). Stiffness is more of a factor at higher frequencies and for floor/ceilings. This is why it's commonly recommended to decouple or mechanically separate a wall with resilient channels, staggered studs, or other specialty products that make it more difficult for vibrations to travel unimpeded through a wall. Stiffness is also why you reach a point of diminishing returns with adding layers of drywall alone to your wall (assuming no other isolation treatments).
2. So now on to the floor/ceiling problem. Unfortunately, sound doesn't travel the same way in air as it does in structures. For example, this is why a concrete slab can be pretty effective at blocking airborne noise (music or voices) but not so great at blocking out impact noise, such as the footsteps of your neanderthal neighbors or the Crossfit gym located directly above your apartment. This is where the isolation or decoupling of the structure really comes into play. Another poster has touched on this, but drop ceilings with resilient hangers, specialty elastic floor underlayments, etc. are all very helpful for making it more difficult for vibrations to transmit through the structure and back out the other side into your house as annoying airborne sound. Aside from the products I mentioned, I would recommend looking into Green Glue and isolating fiberboards such as the ones made by Homasote or Blue Ridge, as products that should hypothetically help improve an existing wall or floor by adding the product + more drywall. Installation is generally a pain for this type of stuff, but they all work pretty well when done properly.
3. New topic - I'd generally recommend insulating interior walls with fiberglass batts (or your fibrous insulation of choice) if you have the chance and value peace and quiet/privacy for the members of your household. You also get the added bonus of having better control of your "microclimates" with respect to heating and cooling the various rooms of your house. A lot of people only use insulation in exterior walls, but I'd argue that it's also important in a lot of interior walls too.
4. Again, to reiterate the path of least resistance point, sound will travel not only through an adjacent wall but also through the adjacent floors and ceilings. If there are weak points in the design, then they will probably be exposed if acoustic performance is important. Ducts and ventilation systems are common things where this pesky detail can come into play once sound enters your duct and completely bypasses that beefy wall you just built to block out noise from an adjacent room.
I can keep going if you want me to. Or you can say uncle if you've had enough of my rambling!