US Patent 7110800 Communication system using short range radio communication headset

In a short range radio communication headset, signals transmitted by the short range radio communications are received while direct sounds propagated from an external are detected. Then, a digital signal adaptation processing using either received signals or the direct sounds as reference signals are applied, and a ratio between the received signals and the direct sounds is controlled by correlating the reference signals and another one of the received signals and the direct sounds that are not used as the reference signals and extracting necessary components.