The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
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Design of Wideband Speech Coder Using the MLT Residual Signal

MLT 여기신호를 이용한 광대역 음성 부호화기 설계

  • Published : 2005.07.01
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Abstract

In this Paper, the structure of a split bandwidth wideband speech coder and its highband coder for tone qualify elevation are Proposed. The lowband and highband by the split bandwidth method are encoded independently applying the G.729E and MLT (Modulated Lapped Transform) residual model. In the highband structure which is encoded by low bit rate of 4kbps, the MLT residual signals are distinguished to voice and unvoice signal . The voice signals are applied to MLT peak picking method by lowband pitch period. Because transformed MLT residual signals are represented by periodic signal that have periodic peak. The unvoice signals are applied to MLT which linear prediction spectral response is added and do vector quantization. Performance for proposed 15.8kbps wideband speech coder was verified through subjective listening test.

본 논문에서는 대역분할 광대역 음성 부호화기의 구조와 음질 향상을 위한 새로운 고대역 구조를 제안한다. 대역분할 방식에 의해 광대역 음성은 저대역 ($O\~4kHz$) 음성과 고대역 ($4\~8kHz$) 음성으로 나뉘어 지고 각각 G.729E와 MLT(Modulated Lapped Transform) 여기모델을 적용하여 서로 독립된 방식으로 부호화한다. 4kbps의 낮은 전송률로 부호화되는 고대역에서는 MLT 여기모델을 효율적으로 이용하기 위하여 유 무성음을 구별하였고 유성음에 대해서는 저대역 피치주기를 이용한 MLT peak picking 방법을 적용하였다. 즉, MLT 변환된 여기신호는 주기적인 피크를 갖는 주기신호로 나타나며 이때의 피크값을 추출하여 양자화하여 전송한다. 무성음에 대해서는 에너지 값에 따라 비트를 달리 적용하고, 선형예측 스펙트럴 응답이 가중된 MLT 벡터 양자화 방법을 적용하였다. 제안된 15.8kbps 광대역 음성 부호화기의 성능평가는 주관적인 음질평가로 선호도 테스트를 수행하였다.

Keywords

References

  1. ITU Radiocommunication Assembly, Document 8 1045-E, 'Detailed specifications of the radio interfaces of IMT-2000,' Document 8 126(Rev. 1), 2000
  2. B. Tang, A. Alwan, 'A perceptually based embedded subband speech coder,' IEEE transactions on speech and audio processing, 5 (2), Mar. 1997
  3. 이우석, 박호종, 손창용, 이영범, '대역폭 계층 구조의 광대역 음성 부호화기 개발,' 음향학회지 23 (6), 481-487, 2004
  4. P. P Vaidyanathan, Multirate Systems and Filter Banks, (Prentice Hall), 189-285, 1993
  5. ITU-T Recommendation. G.729 Annex E, '11.8kbit/s CS-ACELP speech coding algorithm,' Sep. 1998
  6. H. Malvar, 'Fast algorithms for orthogonal and biorthogonal modulated lapped transforms,' 1998 IEEE symposium on, 159-163, Jun. 1998
  7. 3GPP C.S0030-0, 'Selectable mode vocoder service option for wideband spread spectrum communication system,' Dec. 2001
  8. S. Shlien, 'The modulated lapped transform, its timevarying form, and its application to audio coding stands,' IEEE Transactions on speech and audio processing, 4, July 1997
  9. ITU-T Recommendation. G.722.1, 'Coding at 24 and 32kbit/s for hands-free operation in systems with low frame loss,' Sep. 1999
  10. A. K. Soman, P. P. Vaidyanathan, 'Coding gain in paraunitary analysis/synthesis system,' IEEE Transactions on signal processing, 41, 1824-1835, May 1993 https://doi.org/10.1109/78.215302
  11. ITU-T Recommendation. G.722.2, 'Wideband coding of speech at around 16kbit/s using Adaptive Multi-Rate Wide-Band,' 2001