Sound quality degradation of audio equipment by hum noise induced by non-audible high frequency electrical noise

Abstract

In recent audio equipment, induction and inflow of non-audible high frequency (HF) electrical noise to audio equipment is increasing more and more due to implementation of personal computer / network connectivity and high-resolution capability in digital audio equipment. In this study, in order to investigate another causes of influence of non-audible HF electric noise on playback sound, we measured a loudspeaker output of an audio amplifier by the audio analyser with inputting single HF sine wave from a function generator to analog input of the audio amplifier. From measured results, it was found that the power of harmonics of 60 Hz (hum noise) on the loudspeaker output of some audio amplifiers increased when single HF sine wave was inputted. Tendency of the increasing of the hum noise component depended on the frequency of the inputted sine wave and model of audio amplifier. These results show the importance of consideration of HF characteristic and countermeasure to the HF noise also in circuit design and tuning of audio equipment.