A hybrid virtual bass system with improved phase vocoder and high efficiency

Virtual bass has drawn wide attention from consumer electronics manufacturers who demand good bass quality from small loundspeakers that have no low-frequency capability. Based on the missing fundamental phenomena, virtual bass aims to extend the low frequency bandwidth psychoacoustically by generating a series of harmonics in the mid-frequency range where loudspeakers can reproduce well. State-of-the-art virtual bass systems usually combine the phase vocoder (PV) approach and the non-linear device (NLD) approach, which aims to overcome their individual drawbacks and achieve good bass performance through a hybrid approach. However, these bass enhancement approaches still lack in audio quality and computation efficiency. In this paper, we propose a new hybrid system with an improved phase vocoder and high efficiency. Previous studies show that artificially-added harmonics may change the timbre of the sound tracks and damage audio quality. We solve this problem by a subjective preference based harmonic magnitude control (HMC) in PV, which is motivated by a recent study on the relationship between the audio timbre and the relative intensity of harmonics. We also significantly improve the computation efficiency through a fast transient content detector based on constant-Q transform (CQT), a direct FFT/IFFT implementation of PV and a more efficient mechanism of HMC. Experiments show that the proposed approach is five times faster than a recent hybrid approach [1] and achieves the best bass effect and audio quality.