On my car, the blowoff valve is the last thing the airflow hits before going into the engine. The air gets metered by the MAF as soon as it gets through the air filter in my wheel well. Then it goes up to the turbo, does the spin cycle in the compressor and gets pushed down the piping to the intercooler. It goes through the intercooler, comes back up the other side, goes under the blowoff valve and enters the engine through the intake manifold - cold, dense and metered.
And yes the blowoff valve makes that nice "pshhh" sound.