A new 2-kbit/s speech coder based on normalized pitch waveform

Abstract

Speech coding at very low bit-rate is useful for purposes such as voice communication over computer networks. However speech coding at around 2.0 kbit/s is difficult for CELP coders while maintaining a high quality. In this paper, a speech coding model called 'normalized pitch waveform' and its quantization scheme are presented, aiming for effective compression coding of the 'voiced' speech. Listening tests have proven that an efficient and high quality coding has been achieved at 2.0 kbit/s, less than half of the FS1016. Furthermore this paper discusses the disadvantage of the normalized pitch waveform and presents an alternative method of using non-normalized pitch waveform. Encoding of a transitional 'mixed' state between the 'voiced' and the 'unvoiced' state is discussed for further improvements.