LPC VOCODER Using Instants of Significant Excitation and Pole Focusing

  • A. Saranya
  • N. Sripriya
Part of the Communications in Computer and Information Science book series (CCIS, volume 203)

Abstract

Vocoders are designed/used to reduce the bit rate requirement for speech signal transmission without significant degradation in the quality of the resultant speech. In most of the speech coding techniques, the system and the source parameters are coded separately. The system is generally coded using a codebook which demands only less number of bits compared to source coding. Coding of the source parameters requires significant computational complexity and memory to preserve the identity and naturalness of the speaker. In this work, a LPC vocoder is designed which uses the instants of significant excitation estimated from the speech signal to code the source information. Traditional pitch excited LPC vocoders produce intelligible speech at a bit rate of 2400 bps, but they are often synthetic. Hence source is coded by identifying the locations of instants of significant excitation and the corresponding strength at those instants. Thus the bit rate requirement is reduced significantly in the order of 1.6Kbps when a code book of size 1024 is used. The number of bits used for coding the system is further reduced by using the codebook of reduced size, namely 64. But the quality of resynthesized signal decreases as the poles representing the system are defocused due to high averaging. Hence, pole focusing, increasing the radius of the poles is done. This causes the increment in the gain/magnitude of the corresponding frequency component in the spectrum thereby improving the signal quality. Finally, the bit rate requirement is further reduced in the order of 1.3kbps. The performance analysis shows that the resultant synthesized speech is intelligible and quite natural preserving the identity of the speaker.

Keywords

VOCODER LPC Instants of significant excitation pole focusing 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Gold, B., Morgan, N.: Speech and Audio Signal Processing: Processing and Perception of Speech and Music. John Wiley & Sons, Inc., New York (1999)Google Scholar
  2. 2.
    Gold, B., Rader, C.M.: The Channel Vocoder. IEEE Transactions on Audio and Electro Acoustics AU-15(4) (December 1967)Google Scholar
  3. 3.
    Davie, M.C.: Channel vocoder based on c.c.d. discrete-fourier transform Processors. IEEE Proc. 127, pt. F(2) (April 1980)Google Scholar
  4. 4.
    Martins, J.A., Violaro, F.: Low bit rate LPC vocoders using vector quantization and interpolation, pp. 597–600. IEEE, Los Alamitos (1991)Google Scholar
  5. 5.
    David, E.E., Schroeder, M.R., Logan, B.F., Prestigiacoma, A.J.: Voice-excited vocoders for practical speech bandwidth reduction. Presented at the Speech Communication Seminar, Stockholm (1963)Google Scholar
  6. 6.
    Magil, D.T., Un, C.K.: Residual-excited linear predictive coder. JASA 55, Suplement abstract NN3 in the April 24-26 87th meeting of the Acoustical Society, 581Google Scholar
  7. 7.
    Weinstein, C.J.: A linear prediction vocoder with voice excitation. In: Proc. Eascon 1975, Washington, D.C, pp. 30A-30G (1975)Google Scholar
  8. 8.
    Schroeder, M., Atal, B.: Code-excited linear prediction: high-quality speech coding at very low bit rates. In: Proc. ICASSP 1985, Tampa, pp. 937–940 (1985)Google Scholar
  9. 9.
    Ubale, A., Gersho, A.: A multi-band CELP wideband speech coder. In: IEEE Proc. ICASSP 1997, pp. 1367–1370 (April 1997)Google Scholar
  10. 10.
    McCree, A.V., Barnwell, T.P.: A Mixed Excitation LPC Vocoder Model for Low Bit Rate Speech Coding. IEEE Transactions on Speech and Audio Processing 3, 4 (1995)CrossRefGoogle Scholar
  11. 11.
    McCkllan, S.A., Gibson, J.D.: Variable Rate CELP Based On Subband Flatness. IEEE Transactions on Speech and Audio Processing 5(2) (March 1997)Google Scholar
  12. 12.
    Park, Y., Yang, J., Sohn, S., Bae, M.: On a time reduction of pitch searching by the regular pulse search technique in the CELP vocoder. IEEE, Los Alamitos (1997)Google Scholar
  13. 13.
    Sripriya, N., Vijayalakshmi, P., Arun Kumar, C., Nagarajan, T.: Estimation of Instants of Significant Excitation from Speech Signal using Temporal Phase Periodicity. In: IEEE TENCON 2009 (2009)Google Scholar
  14. 14.
    Yang, G., Leich, H.: A Robust and Fast DP-CELP (Double-Pulse CELP) Vocoder at the Bit Rate of 4 kbh. In: International Symposium on Speech, Image Processing and Neural Networks (April 13-16, 1994)Google Scholar
  15. 15.
    Rabiner, L., Juang, B.-H., Yegnanarayana, B.: Fundamentals of Speech Recognition. Pearson Education, London (1993)Google Scholar
  16. 16.
    Wei, B., Gibson, J.D.: Comparison of distance measures in discrete spectral modeling. In: Proc. 9th DSP Workshop & 1st Signal Processing Education Workshop (2000)Google Scholar
  17. 17.
    Rabiner, L.R., Schafer, R.W.: Digital Processing of Speech Signals. Prentice-Hall, Inc., Englewood Cliffs (1978)Google Scholar
  18. 18.
    Abraham, A., Vijayalakshmi, P., Nagarajan, T.: Pole-focused linear prediction-based spectrogram for coarticulation analysis. In: IEEE TechSym, pp. 94–97 (2010)Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • A. Saranya
    • 1
  • N. Sripriya
    • 1
  1. 1.Department of Information TechnologySri Sivasubramania Nadar College of EngineeringChennaiIndia

Personalised recommendations