What we needed: sound isolation for a music room/living room.
My wife and I being opera singers (and I having been assaulted in the past for practicing at home (this was in a different country)), I know the need of acoustic isolation, both for my own mental well being (a singer cannot sing well when one is always worried if he is disturbing the neighbours), and for the well being of my neighbours.
Searching online and at music stores, I called the one place that had the best reviews for musicians and regular people alike, SORGEDIL. I am glad I did.
After initial contact, the acoustician came over, made measurements (both with us singing and with ambient sound), made his recommendations based on our needs/budget (this was pre-COVID), and (with that estimate in hand) we had the ceiling done and they created a door and frame in an archway into the living room. We were adamant that we did not want a 'recording studio' feel to the music room/living room, but we needed a good level of soundproofing. This was in 2018/2019. When the work was done it was excellent (although the workers for the ceiling were a bit sloppy during the process (smashing the gate sensor in the driveway (which they did repair after a phone call to Sig. Sorge)) the end result was FANTASTIC. When the door was ready (only delayed due to Christmas/New Year), it was installed and adjusted expeditiously (these workers were consummate professionals). Afterwards, I spoke to the neighbours and they were all complimentary about the lack of sound coming from our new apartment (I'm a Wagnerian singer, so that's a huge compliment for SORGEDIL).
Jump to 2020. The neighbours upstairs are home all the time now, blast techno music, and walk and speak loudly which can be heard through a shared vertical wall (again, this was not a problem pre-COVID restrictions/lockdown because they were at work during the day which allowed me to teach/practice in peace). If we can hear that, then they can surely hear us.
This is, of course, a problem when teaching online and making recordings (to be fair, the neighbours (including upstairs) are very tolerant of our needs to practice/do online teaching/make recordings, but they don't understand that someone else's techno or shouting isn't conducive to a good lesson/recording).
It is obvious that what was predicated on life pre-COVID needed to be updated. And so, we've spoken to SORGEDIL again (the owner called me back within an hour of sending my email explaining what I needed) and we will be making an appointment for further work (walls and possibly windows, if we can afford it), not because of any insufficient work done previously, but because of the PROFESSIONALISM of the work already done and their understanding our need, budget, and financial limitations.
I recommend SORGEDIL...highly.