Multi-pulse type coding system with correlation calculation by backward-filtering operation for multi-pulse searching

• US 5,202,953 A
• Filed: 01/21/1992
• Issued: 04/13/1993
• Est. Priority Date: 04/08/1987
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Taguchi, Tetsu
• Primary Examiner(s): Knepper, David D.
• Application Number:
  US07/823,615
• Time in Patent Office: 448 Days
• Field of Search: 381/29-40, 381/48-50, 395/2
• US Class Current: 704/200
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation

Abstract

Speech signal encoding at a low bit rate is realized by decreasing the number of arithmetic operations required to determine LPC parameters in a backward processing unit. These parameters are determined and updated by filtering, rather than by impulse response. In this manner, it is not necessary to use previously-calculated parameters in updating.

Claims

1. A multi-pulse type coding system for coding a speech signal into a plurality of pulse signals, comprising:

means for producing one set of parameters indicative of a spectral envelope of said speech signal for each search frame period;

means, coupled to said parameter producing means and responsive to a plurality of sets of parameters, each of said sets of parameters belonging to adjacent search frame periods, for producing a plurality of sets of interpolated parameters during each search frame period;

means for extracting a segmented speech signal from said speech signal and for delivering said segmented speech signal in backward time sequence, said segmented speech signal having a period corresponding to said each search frame period;

means for filtering said segmented speech signal in accordance with a filtering characteristic defined by said set of parameters and said plurality of sets of interpolated parameters during said each search frame period and for directly producing a cross-correlation signal representative of a transition of cross-correlation between said segmented speech signal and an impulse response defined by said set of parameters and said sets of interpolated parameters during said each search frame period, said filtering characteristic being varied during said each search frame period in accordance with a backward time sequence of said set of parameters and said plurality of interpolated parameters, said segmented speech signal being received in backward time sequence; and

means for generating said plurality of pulse signals in response to said cross-correlation signal.

2. A multi-pulse type coding system as claimed in claim 1, further comprising

means for transmitting said parameters delivered from said parameter producing means and information representative of said plurality of pulse signals.

3. A multi-pulse type coding system as claimed in claim 1, wherein said parameters are LPC coefficients.

4. A multi-pulse type coding system as claimed in claim 1, wherein said means for producing a plurality of sets of parameters includes interpolating means for producing a plurality of interpolated parameters during said search frame period from said parameters associated with two adjacent search frame periods.

5. A multi-pulse type coding system for coding a speech signal into a plurality of pulse signals, comprising:

LPC analyzer means for producing one set of LPC parameters indicative of a spectral envelope of the speech signal for each search frame period;

interpolation means responsive to said one set of LPC parameters and another set of LPC parameters for an adjacent search frame period for producing a plurality of interpolated LPC parameters during said search frame period;

means for receiving said speech signal in backward time sequence;

filter means for backwardly filtering said speech signal under control of said LPC parameters and said interpolated LPC parameters to produce cross-correlation between said speech signal and an impulse response defined by said LPC parameters of said interpolated LPC parameters, said cross-correlation being representative of a correlative transition during said each search frame period, a filtering characteristic of said filtering means being varied during said each search frame period in accordance with a backward time sequence of said LPC parameters and said interpolated LPC parameters, said speech signal being received in backward time sequence; and

search means for searching said plurality of pulse signals in response to said cross-correlation.