A multi-channel real-time sound pressure spectrum analyzer was demonstrated to investigate abnormal noises of tapered roller bearings (TRBs) because of friction and wear or other reasons. The sound sensing system developed is to replace the existing quality-control method conducted by human ears. The high frequency band of abnormal noises of TRBs were confirmed as 2.0~2.5kHz that can be hardly detected by human ears due to the lower sound pressures. Background interferences, including surrounding environment (less than 400Hz), motor (850~900Hz) and friction (400~600Hz) noises, were defined and eliminated. All the data collected by the sensing system were performed by using fast Fourier transform (FFT).