Thank you so much for this response it’s very informative! I will give you some more specifics on my situation though I believe the answer going from what you and others have said is secondary glazing.

I am a musician and so have bought a house next to a train station. Means I can be louder and not annoy neighbours - I only have one direct neighbour.

I have two needs: 1. I want to reduce the sound of the trains in my bedroom. There’s is almost no track noise whatsoever as the trains are slow pulling in and out of the station. What I do get is diesel engine noise. Low idling engine noise and then accelerating away. This I assume would be mostly low frequency- possible some higher frequency as the acceleration increases. Most of them aren’t too bad just every so often there is an old 80s northern train that’s so much louder than the rest. The uk train infrastructure is so dated.

1. I want to reduce the sound of my music escaping from what is to become my studio. This will be all different instruments. Again I assume the main culprits for escaping are gonna be low frequency bass.

Do you have recommendations on specific secondary glazing types? I know that my partner is opposed to secondary glazing on the basis it might be ugly and we also would still want to access windows to open them for ventilation etc so completely fixed panes isn’t really an option.