Performance of comb filtering noise reduction method and application to quality improvement in PCM speech

Abstract

This paper proposes a method f o r reduci n g a d d i t i v e n o i s e from noisy speech s i g n a l . The e f f e c t i v e n e s s of t h i s comb f i l t e r i n g method i s demonstrated v i a experiments. The method i s a p p l i c a b l e t o n o i s e with varying power and non-flat spectrum. L i s t e n i n g experiments show t h a t t h e proposed method improves the s u b j e c t i v e SIN and t h e sound a r t i cu l a t i o n of extremely noisy speech. t i o n of t h i s method f o r t h e r e d u c t i o n of q u a n t i z a t i o n n o i s e and n o i s e caused by b i t e r r o r i n PCM speech i s i n v e s t i g a t e d . mental r e s u l t s i n d i c a t e t h a t : Applica-Experi-(1) For e r r o r -f r e e 2-to-5 b i t PCM t h e proposed method improves t h e s u b j e c t i v e quali t y of t h e speech equivalent t o one b i t ; (2) For b i t e r r o r r a t e 'ranging from 10-3 t o 10-1, t h e proposed method improves t h e q u a l i t y of 8-bit PCM speech e q u i v a l e n t t o t h e reduction of e r r o r rate down t o about 1 / 3 -1 / 5 . It i s very e f f e c t i v e f o r reducing t h e quantiz a t i o n noise i n 4-bit PCM speech. (3) The proposed method i s p a r t i c u l a r l y u s e f u l f o r improving t h e sound a r t i c u l a t i o n of extremely noisy speech. 1. I n t r o d u c t i o n Speech s i g n a l s i n communication and audio systems u s u a l l y are contaminated by noise. Noise causes degradations i n t h e q u a l i t y of speech s i g n a l s and reduces t h e performances of audio processing equipment. Therefore , r e s e a r c h and development of techniques f o r n o i s e r e d u c t i o n a r e v e r y important. Noise reduction methods proposed previously include Wiener f i l t e r i n g , a d d i t i v e noise c a n c e l i n g [13 , s p e c t r a l s u b t r a c t i o n [2-41 , method based on c o r r e l a t i o n [5] , and speech modeling [ 6 ] . These methods assume t h a t t h e power and spectrum of n o i s e are known v a l u e s . The comb f i l t e r i n g n o i s e red u c t i o n method proposed by t h i s paper does n o t have t o r e l y on such assumptions. Even though comb f i l t e r i n g method h a s been used i n t h e p a s t [ 7-91 , comprehensive q u a n t i t a t i v e e v a l u a t i o n p e r t i n e n t t o p i t c h e x t r a c t i o n of noisy speech and removal of harmonic noise has not been presented. The n o i s e reduction method proposed h e r e u t i l i z e s t h e p i t c h ext r a c t i o n [ l o ] and comb f i l t e r i n g techniques

Optimum filter theory for quasi‐periodic signals

“…In general, a constant-BW (bandwidth) comb filter is used, consisting of bandpass filters with equal bandwidths at each harmonic tone. Methods of configuration include the short-time Fourier transform [3] and the IIR type [4]. In particular, the IIR type is the most widely used because of its sharp filter response with few stages.…”