Speech Enhancement by Formant Sharpening in the Cepstral Domain

This paper presents a method for enhancing speech signals in the root cepstral domain, typically in conjunction with the cepstral subtraction technique. The effect of the processing is similar to the spectral sharpening method performed in the time domain, but with a much lower computational requirement when combined with cepstral subtraction and with better performance. The portions of the signal corresponding to frequency formant peaks are further amplified, while formant valleys are attenuated, with the aims of further reducing noise in those regions and improving speech quality. The cepstral procedure maintains the spectral tilt of all speech segments, unlike the time domain approach which only attempts to maintain the long-term average spectral tilt. The scheme was devised as part of an enhancement system designed for forensic speech enhancement, where speech intelligibility is an important consideration.