 To overcome this, a high frequency signal, known as bias, is mixed in with the recorded signal, which "pushes" the envelope of the signal into the linear region.If the audio signal contains strong high frequency content, in particular from percussion instruments such as a high-hat, this adds to the constant bias causing magnetic saturation on the tape.Dolby HX Pro automatically reduces the bias signal in the presence of strong high frequency signals, making it possible to record at a higher signal level, leading to its name