A physically motivated room reverberation enhancement system that is stable in any (dissipative) room: An application of sound portholes

摘要

Prior active room reverberation enhancement systems have typically employedrnmicrophones, artificial reverberator filters, and loudspeakers to change the reverberantrnproperties of a room. However, acoustic feedback from the loudspeakers to thernmicrophones has had the potential to drive such systems unstable. To avoid feedbackrninstabilities, we apply passivity techniques from control theory to design a stable roomrnreverberation enhancement system from the ground up. In particular, we employ soundrnportholes, which are special transducers that operate concurrently as microphones andrnloudspeakers. With these sound portholes, the feedback controller implements a passivernconnection to virtual acoustic spaces, which are realized using digital waveguide networks.rnBecause the feedback controller models a passive system, it is theoretically stable in anyrn(dissipative) acoustic environment and for arbitrarily large loop gains. As a consequence,rnthe system does not suffer from “ringing tones” at high loop gains in the same way as priorrnsystems have suffered. Furthermore, the system does not need to be re-calibrated if thernproperties of the room change or even if moved to a whole new room. This method forrndesigning room reverberation enhancement systems may generally result in more realisticrnreverberant sound because it implements the acoustical features of a system that couldrnexist naturally in the physical world.