Jabra Link 850 AmplifierDual connection. PCs (via USB), desktop telephones or both at the same time. Advanced noise reducing technology for a better call by reducing background noise. Removes line hiss, buzz and other distracting noises from the phone network. Digital Signal Processing (DSP) for crystal clear natural sound. Automatically adjusts call volume to a comfortable level with no distortion. Acoustic shock protection Prevent harm to the user from sudden loud noises