Method of encoding speech signals using a multipulse excitation signal having amplitude-corrected pulses

• US 4,847,905 A
• Filed: 03/24/1986
• Issued: 07/11/1989
• Est. Priority Date: 03/22/1985
• Status: Expired due to Fees

• Current Assignee: Societe Anonyme DBA
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: Lefevre, Jean-Paul, Passien, Olivier
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): Anderson, Lawrence E.
• Application Number:
  US06/843,487
• Time in Patent Office: 1,205 Days
• Field of Search: 375/26, 381/36, 381/38, 381/39, 381/47, 381/50, 381/51, 364/513.5
• US Class Current: 704/222
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation

Abstract

In a digital speech encoding system wherein the transmitter substitutes for the original speech signal to be encoded (1) certain parameters supplied by an analysis circuit defining, within successive time frames, the characteristics of a synthesis filter modeling the vocal tract and located at a receiver connected to the transmitter via a low-bit-rate data link, and (2) a multipulse excitation signal intended for said synthesis filter and supplied by a pulse generating circuit which determines the pulse position and amplitudes by successive approximation minimizing the mean squared error between the original speech signal and the synthetic speech signal obtained from the filter, the pulse generating circuit adds to the amplitude of each of the pulses, at the end of the approximation routine, a corrective term that is a function of the value of the partial derivative of the mean squared error taken relative to the amplitude of the pulse under consideration, taken as an independent variable.

Claims

1. A low-bit-rate encoding method of the type comprising the steps of receiving an input signal representing speech to be encoded, generating in response to said input signal a plurality of parameters defining, for successive time frames, the characteristics of a synthesis filter modeling the vocal tract, generating a multipulse excitation signal for said filter comprising a plurality of pulses having positions and amplitudes determined by successive approximation according to the criterion of the minimization of the means squared error between the original speech signal to be encoded and a synthetic speech signal to be produced by said filter, said method further comprising, after determining the positions and amplitudes of said pulses by successive approximation, the further step of adding to the amplitude of each pulse a correcting term based on the value of the partial derivative of the mean squared errror with respect to the amplitude of said each pulse taken as an independent variable, said method further comprising weighting said mean squared error by filtering in a perceptual filter whose impulse response is defined relative to that of said synthesis filter, wherein the corrective term added to the amplitude of each of the pulses determined by successive approximation is proportional to the partial derivative of the weighted mean squared error carried out with respect to the amplitude of the pulse under consideration taken as an independent variable and divided by the value for zero of the autocorrelation function of the impulse response of the perceptual filter delayed by an amount of time corresponding to the position of the pulse under consideration in relation to the start of the time frame.