Abstract: A process of implementing a low frequency of an audio signal includes the steps of collecting a fundamental frequency from the audio signal at a low frequency region thereof, generating a controlled 2nd harmonic, a controlled 3rd harmonic, and a controlled 4th harmonics respectively based on a 2nd harmonic, a 3rd harmonic, and a 4th harmonic in responsive to the fundamental frequency, and generating a final output signal from a combination of the controlled 2nd harmonic, the controlled 3rd harmonic, and the controlled 4th harmonic. In which, the output signal is generated correlating with a loudness of the fundamental frequency to enhance the bass performance of an audio system device.