Method and apparatus for speech encoding, speech decoding, and speech post processing

• US 5,596,675 A
• Filed: 09/13/1995
• Issued: 01/21/1997
• Est. Priority Date: 05/21/1993
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Ishii, Jun, Takahashi, Shinya
• Primary Examiner(s): Tung, Kee M.
• Application Number:
  US08/527,575
• Time in Patent Office: 496 Days
• Field of Search: 395/2.2, 395/2.16, 395/2.17, 395/2.25-2.32, 395/2.35, 395/2.67, 395/2.71-2.73, 395/2.42, 395/2.43, 395/2.78, 387/36-40, 387/46.51
• US Class Current: 704/211
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• 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 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering

Abstract

A speech analysis unit and a window locating means are implemented in a speech coding apparatus. The speech coding apparatus encodes input speech per analysis frame defined having a fixed length and is offset at fixed interval. The speech analysis unit extracts frequency spectrum characteristic parameters of the input speech taken within an analysis window. The location of the analysis window is specified by the window locating means. The window locating unit selects the location of the analysis window which is used in extracting the frequency spectrum characteristic parameters at the speech analysis unit. In this case, depending upon the characteristic parameter of the input speech within and near the frame concerned, the window locating unit selects the location of the analysis window within the range which is not to be exceeding the range of the frame concerned.

Claims

1. A speech coding apparatus for coding an input speech signal within an analysis window of an analysis frame, comprising:

(a) window locating means for defining a plurality of analysis windows at different locations in the analysis frame, the window locating means including

means for receiving a segment of the input speech signal within each of the analysis windows,

means for calculating a predefined feature of the segment of the input speech signal within each analysis window,

means for comparing the calculated features of each analysis window, and

means for selecting an analysis window based on a result of the comparison;

(b) speech analysis means for extracting characteristic parameters of the input speech signal in the selected analysis window selected by the window locating means; and

(c) coding means for receiving the characteristic parameters and for encoding the characteristic parameters.

2. The speech coding apparatus of claim 1, wherein the predefined feature is a power of the input speech signal, and wherein an analysis window having a maximum power value is the window selected.

3. The speech coding apparatus of claim 1 or 2, wherein the speech analysis means comprises:

means for providing a second analysis window different from the selected analysis window; and

means for calculating a value of power of the input speech signal within the second analysis window and for outputting the calculated power value to the coding means.

4. The speech coding apparatus of claim 3, wherein a center of the second analysis window is placed at a center of the analysis frame.

5. The speech coding apparatus of claim 3, wherein the analysis frame has a fixed frame length and the second analysis window has a window length which is substantially the same as the analysis frame length.

6. The speech coding apparatus of claim 1, wherein the selected analysis window is the window having a center which is substantially in the center of the analysis frame.

7. The speech coding apparatus of claim 1, wherein the analysis frame has a fixed length and the analysis window has a window length which is substantially the same as the frame length.

8. The speech coding apparatus of claim 1, wherein the predefined feature is a spectrum of the input speech signal of each analysis window and wherein the comparison is a comparison of the spectrums of each analysis window.

9. The speech coding apparatus of claim 1, wherein the predefined feature is an auto correlation of the input speech signal within each analysis window and wherein an analysis window having an auto correlation function having periodicity is the window selected.

10. A speech coding method for encoding input speech within a selected analysis window of an analysis frame, comprising the steps of:

(a) creating an analysis window having a location in the analysis frame;

(b) calculating a value of power of a segment of the input speech signal within the analysis window;

(c) repeating the above steps, such that a plurality of analysis windows are created at a plurality of different locations within the analysis frame;

(d) comparing the power values of each of the plurality of analysis windows and selecting an analysis window of the plurality of analysis windows having a maximum power value.

11. The speech coding method of claim 10, further comprising the steps of:

(a) extracting characteristic parameters of the input speech signal within the selected analysis window;

(b) creating a second analysis window and calculating a value of power of the input speech within the second analysis window; and

(c) encoding the extracted characteristic parameters and the calculated power.

12. The speech coding method of claim 11, wherein the step of creating a second analysis window includes a step of positioning a center of the second analysis window at a center of the analysis frame.

13. The speech coding method of claim 12, wherein the step of creating a second analysis window includes a step of setting a length of the second analysis window substantially the same as a length of the analysis frame.

14. A speech coding method for coding an input speech signal comprising the steps of:

receiving a segment of the input speech signal corresponding to an analysis frame of the input speech signal;

creating a plurality of analysis windows at different locations within the analysis frame;

for each one of the plurality of analysis windows, calculating a value of power of the input signal contained within the one of the plurality of analysis windows;

comparing the value of power of each of the plurality of analysis windows;

selecting an analysis window of the plurality of analysis windows having a greatest value of power.

15. The speech coding method of claim 14, further comprising the steps of:

extracting characteristic parameters of the input speech signal within the selected analysis window.

16. The speech coding method of claim 14 further comprising the steps of:

creating a second analysis window within the analysis frame, wherein the second analysis window has a center substantially in the center of the analysis frame; and

encoding the extracted characteristic parameters and the calculated power.