To some people it’s obvious. To many others, it’s a bit more hazy.
Acoustic treatment is not the same as soundproofing.
Not even a little bit. Yet, often I see the terms being used interchangeably. Or one term used when the other’s meaning is intended.
Acoustic treatment is about controlling how sounds behave inside the room. How and where they reflect, which frequencies are absorbed and how effectively, and (if you’re lucky) how the dimensions of the room affect its resonant behaviour. Acoustic treatment is about whether a room sounds lively, echoey, dead, boxy, etc.
Acoustic treatment usually involves controlling the quality of the surfaces – whether they’re hard (reflective) or soft (absorbent) and whether they’re flat (echoey) or curved (diffuse). If you’re lucky, you get to influence the size and shape of the room to control its resonant behaviour.
Soundproofing, on the other hand, is about how much sound gets in or out of the room. It’s about reducing the level of cars or birds or neighbours in your recordings. It’s also about reducing the degree to which your neighbours can hear you.
Soundproofing usually involves making sure all the walls are of a thick and solid construction (i.e. brick or concrete). It also involves stopping all the air gaps where sound can travel in or out of the room.