huit

Or if you don't want to do something drastic like messing with the boost pressure (most people dial up the boost pressure to go faster and not to make noise), and all you want to achieve is louder noise, get a riceboy style BOV with a trumpet attached to the nozzle to amplify the sound (Blitz makes some good ones), or relocate the BOV closer to the turbo so there's less pressure drop, or relocate it closer to the outside of the engine bay so the sound deadening material under the bonnet won't muffle the noise (eg near the intercooler)

While a higher boost pressure will definitely result in louder noise as the BOV discharges - you cannot say categorically 0.3-0.4 bar would produce inaudible blow-off noise - there are too many factors involved.

But first of all, you need to establish whether you car has a BOV at all - most cars come from the factory with a bypass valve that vents the charged air back to the intake, because in most jurisdictions BOVs are illegal.