Scooby Jimmy

Hi all i'm new to the forum, i have a 2004 Impreza WRX, i left work yesterday and the car was only boosting to 0.5bar instead of the usual 0.9bar, there is no knocks, bangs, hesitation, !Removed! down etc. the engine is running standard power and has never caused me any issues in the past. has anyone had this fault/issue before?