Reduction of musical residual noise using block-and-directional-median filter adapted by harmonic properties

• Musical residual noise can be efficiently removed by post-processing.
• Block-median filtering can significantly remove musical tones.
• A post-processor adapted by harmonic properties can well maintain vowel quality.

Many speech enhancement systems can efficiently remove background noise. However, most of them suffer from musical residual noise which is very annoying to the human ear. This study proposes a post-processing system to efficiently reduce the effect of musical residual noise, enabling the enhanced speech to be improved. Noisy speech is firstly enhanced by a speech enhancement algorithm to reduce background noise. The enhanced speech is then post-processed by a block-and-directional-median (BDM) filter adapted by harmonic properties, causing the musical effect of residual noise being efficiently reduced. In the case of a speech-like spectrum, directional-median filtering is performed to slightly reduce the musical effect of residual noise, where a strong harmonic spectrum of a vowel is well maintained. The quality of post-processed speech is then ensured. On the contrary, block-median filtering is performed to greatly reduce the spectral variation in noise-dominant regions, enabling the spectral peaks of musical tones to be significantly smoothed. The musical effect of residual noise is therefore reduced. Finally, the preprocessed and post-processed spectra are integrated according to the speech-presence probability. Experimental results show that the proposed post processor can efficiently improve the performance of a speech enhancement system by reducing the musical effect of residual noise.