An audio converting device including a digital high-pass filter, an expander, a digital low-pass filter, a delta-sigma modulator, a digital-to-analog converter, an analog low-pass filter and a gain control unit is provided. The digital high-pass filter in this invention can filter out a direct-current...http://www.google.com/patents/US7181028?utm_source=gb-gplus-sharePatent US7181028 - Audio converting device and converting method thereof
