Improvements of background sound coding in linear predictive speech coders

Abstract

A proper coding of background sounds has proven to be important in digital cellular telephone systems. It is therefore of considerable interest to find methods that improve also background sound coding, in particular in medium and low bitrate speech coders. In many coders operating around 8 kbps, one signifi cant effect has been a swirling distortion when coding for example smooth car noise. The paper discusses the origin of this problem, and presents an algorithm that reduces swirling, giving a significant overall perceptual improvement, as shown by field tests in commercial D-AMPS systems in the US. A related new algorithm for error concealment is also pre sented. This method makes it possible to perceptually remove the effect of fading dips persisting for a few sec onds, during nonspeech periods.

Frame level noise classification in mobile environments

“…For example, the accuracy of a speech recognition device might severely be affected if the level of noise is high and there is a mismatch between training and operation conditions [l]. In speech coding, background noises can be coded with annoying artifacts [2].…”

An improved background noise coding mode for variable rate speech coders

“…The ITU-T Study Group 12 (Question 17 "Noise aspects in evolving networks") is currently studying the effect of background noise in voice communications systems [5]. Moreover, some speech coders fail to handle background noise resulting in unnatural-sounding artifacts to the listener [6]. Recently, Beritelli [4] has proposed a multi-mode noise coding scheme with bit rates from 0-4.9 kbps as part of a CS-ACELP VBR coder.…”