sound card - VU meter web application - Super User

i want vu meter web app can detect sound levels system's mic. suggestions?

with flash actionscript 3 can so:

[ addeventlistener(event.enter_frame, onenterframe);  private function onenterframe(ev:event):void {    activitylevel.setprogress(mymic.activitylevel, 100); }    ] 

where activitylevel progressbar object , mymic mic. , add event listener on constructor of class.