On the DV, it says blow-off valve. you can leave the top pipe off to get some sounds (never did it). The sound is same as stock for me, but if you want the sound people said you should get a CAI and you'll get it.
get a CAI- our cars run better w/ that set up over getting a BOV. You are gonna get some mixed opinions but most will agree that a BOV is not a good idea on 1.8t, you can hold more boost by not venting what pressure you already have into the atmosphere(what the BOV does). DV simply recirculates the same air. I went w/ a Velocity CAI and its every bit as loud as having a BOV, cause any excess pressure ( like when you take your foot off of the gas) is directed back to the air intake, resulting in the WHOOOOSH sound you are looking for. if you wanna more technical explanation, i'm sure the search will help you just fine.