Patent ID: 7529662

Claim:
A method for transcoding a bit stream encoded according to a linear predictive coding (LPC) standard to a bit stream encoded according to a mixed-excitation linear prediction (MELP) standard, comprising: decoding a bit stream into a first set of vocoder parameters compatible with the LPC standard; transforming the first set of vocoder parameters into a second set of vocoder parameters compatible with the MELP standard without converting the first set of vocoder parameters to an analog or digital waveform representation, wherein the transforming comprises converting LPC spectrum, voicing, pitch, and gain parameters to MELP spectrum, voicing, pitch, and gain parameters, and the converting of LPC spectrum parameters to MELP spectrum parameters comprises removing preemphasis effects from LPC spectral coefficients, and the removing of preemphasis effects comprises converting LPC reflection coefficients (RC) to their equivalent normalized autocorrelation coefficients (R); storing the autocorrelation coefficients (R) symmetrically in a first array; and convolving the first array with a second array storing symmetrical autocorrelation coefficients (HH) of a deemphasis filter, thereby producing a deemphasized set of autocorrelation coefficients (R′); and encoding the second set of vocoder parameters into a bit stream compatible with the MELP vocoder standard.