My last remodel job, before I retired, was a $200,000.00 remodel of an 80 year old farm house.  The house was several miles outside of Tinino, Washington. The owners lived in New York.  They, basically, said, "fix it" and left me a LOT of free reign on how that came to be.  Months into the project, the flew out, concerned about the time it was taking. They went back home happy.  

I flooded their email with photos and detailed invoices.  They had all the minute details of the granite window sills, 8' deep French drain (12" drain pipe with wells). The saw the interior and exterior of the entire back wall torn into. They saw the kitchen one architect said couldn't be done, but which the second said was perfect (open beam ceiling). After their visit, they said, keep playing. . . .

On that kitchen, I played a lot.  Like much of the rest of the house, I took it back down to framing. Then I sheathed it and covered that with Tyvec. I followed the rules about taping every cut and tear with specialty tape designed for Tyvec, to stop air movement. 

Meanwhile, true to my rabbit trail inclinations, I started diving deep into sound control.  Partially, I went down certain sound roads because of inspiration born of stupidity of a former boss, who didn't even bother packing the gaps around newly installed windows with insulation, or non-expanding foam, making it possible to carry on normal conversations between people inside and outside the house.

The rabbit trails reminded me sound was air movement (rarefaction and compressions of air waves), so stopping air movement meant stopping sound. 

I couldn't put the vacuum of space in the walls, but there were other things I could do. Some on my own dime (labor wise), because I wanted to know.

Just having the walls sheathed and Tyvec covered went a long ways to sound control via stopping air movement.  On a whim, and because I bought my good quality caulk by the case anyway, I spent several hours caulking (with foam backer, when needed) everything on the inside of the open walls that it appeared could contribute to air infiltration.

Yeah, when I goof off, I REALLY goof off.

Interestingly, I was working alone one day and hadn't turned the radio on (thought I'd actually see what kind of strange things were being rambled about in my head).  I was working in the kitchen, where I had installed three windows and a French door.  It was REALLY quiet. HOWEVER, I opened the French door to toss something on the deck and was met with a raging storm I did not know was going on.  

Now, imagine adding carefully laid insulation and sheet rock to those walls.  I'd be well on the way to soundproofing the house from the wild outdoors.

This got me even more interested in sound proofing. For example, the farm house was to become a remote (in the woods) office and meeting place for a large land conservation trust (great way to convert your secluded acreage into a peaceful retreat you could actually get government grants to improve).  

That meant bathrooms accessible to visitors were needed. Because I hate most architects ability to think about businesses customers and privacy when it comes to commercial bathrooms (doors that open on to urinals, etc.), I wanted cover the ____sses of visitors. I actually added a tread plate to the bottom of the bathroom door. I gave the exhaust another intake option, other than from under the standard, large gap bathroom door.  

I did the extra sheet rock thing too. That is, adding mass, so the wall to the hallway off the main hall did not as readily act like a speaker diaphragm when someone who had, earlier, left Taco Bell to tend a meeting at the trust headquarters used the facilities. 

In the end, sealing against air movement was the one, biggest improvement to that old 2,500 square foot, single story farm house, whether by way of Tyveck, caulk, spray foam, sheet rock or good tread plates. That's because walls can't transfer sound if they don't, first, get hit with air to turn them into speaker cones (or what have you's).