Code-Excited Linear Prediction (CELP)

Vector Quantization of LPC

  • A single code is transmitted rather than a sequence of coded scalar parameters
  • Typically 10 bit codebooks and 10 LPC coefficients
  • Searching the VQ vector by measuring the spectral distance between the input vector and every vector in the codebook
  • Scalar coding can be used for pitch and/or gain

    Basic Principles of CELP

    What is the advantage of VQ?

  • Produces low-rate but high-quality speech
  • The error signal is transmitted



  • CELP uses standard LPC filters but with a VQ-guided excitation
  • Short sections of the risidual waveform (up to 5 ms) are coded with typically 10 bit codebooks ( i.e. there are 1024 excitation vectors instead of 2)
  • Finding the optimal excitation vector is similar to finding optimal LP vectors, i.e. minimizing the squared error