Method and apparatus for speech coding

• US 5,001,759 A
• Filed: 09/27/1989
• Issued: 03/19/1991
• Est. Priority Date: 09/18/1986
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Fukui, Akira
• Primary Examiner(s): KEMENY, EMANUEL
• Application Number:
  US07/414,643
• Time in Patent Office: 538 Days
• Field of Search: 381/34-49
• US Class Current: 704/216
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation

Abstract

A multi-pulse speech coding method and apparatus capable of encoding speech at a bit rate of 16 kbps or less. The method determines the location and amplitude of a pulse by searching through all of the samples of a criterion function, modifying all of the samples of the criterion function, and them repeating the pulse search. After the predetermined number of pulses have been determined, the method modifies the amplitude of the determined pulse, modifies the criterion function at the location where the pulses are set, and repeats such pulse amplitude modification. The method is, therefore, capable of modifying a pulse amplitude by using only a minimum amount of computation. As compared to the amount of computerization required by a method of the kind which modifies pulse amplitude in a pulse search loop.

Claims

1. A speech coding system comprising:

means for applying a linear predictive analysis to an input signal;

means for producing an impulse response of a linear predictive filter;

means for producing an autocorrelation function of said impulse response;

means for producing a crosscorrelation function between said input signal and said impulse response to use said crosscorrelation function as a criterion function;

pulse search means which sets a first pulse at a location where the criterion function is maximum, and produces a first normalized autocorrelation function of an impulse response by multiplying said autocorrelation of the impulse response by an amplitude of the pulse, and which renews said criterion function by subtracting said first normalized autocorrelation function of the impulse response from said criterion function centering around a location where the pulse is set, and which iteratively determines a predetermined number of pulses in the same manner based on said criterion function, and which modifies the amplitude of the pulse set at a location, among the locations where the pulses are set, said location being an absolute value of said criterion function is maximum, and which produces a second normalized autocorrelation function of the impulse response, in accordance with only the locations where the pulses are set, by multiplying said autocorrelation of the impulse response by the modified amount of the pulse, and which renews said criterion function by subtracting said second normalized autocorrelation function of the impulse response from said criterion function, at only the locations where the pulses are set, centering around the location where the pulse amplitude is modified, and repeats pulse amplitude modification a predetermined number of times based on said criterion function; and

output means for outputting the coefficients of the linear predictive filter and the locations and amplitudes of the predetermined number of pulses.