Multimode speech coding apparatus and decoding apparatus

• US 7,577,567 B2
• Filed: 12/12/2006
• Issued: 08/18/2009
• Est. Priority Date: 01/11/2000
• Status: Expired due to Term

• Current Assignee: III Holdings 12, LLC (Intellectual Ventures LLC)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Ehara, Hiroyuki
• Primary Examiner(s): Chawan, Vijay B
• Application Number:
  US11/637,128
• Publication Number:
  US 20070088543A1
• Time in Patent Office: 980 Days
• Field of Search: 704/219, 704/222, 704/228, 704/223, 704/220, 704/221, 704/212, 704/230
• US Class Current: 704/223
• CPC Class Codes: G10L 19/07 Line spectrum pair [LSP] vocoders
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 2025/783 based on threshold decision

Abstract

Square sum calculator 603 calculates a square sum of evolution in smoothed quantized LSP parameter for each order. A first dynamic parameter is thereby obtained. Square sum calculator 605 calculates a square sum using a square value of each order. The square sum is a second dynamic parameter. Maximum value calculator 606 selects a maximum value from among square values for each order. The maximum value is a third dynamic parameter. The first to third dynamic parameters are output to mode determiner 607, which determines a speech mode by judging the parameters with respective thresholds to output mode information.

Claims

1. A speech decoding apparatus comprising:

a decoder that decodes a code representing a quantized LPC and generates a decoded LSP parameter for a current frame;

a mode determining apparatus that calculates an average decoded LSP parameter in a period in which a decoded LSP parameter is stationary and determines whether the current frame indicates a speech mode or non-speech mode utilizing the average decoded LSP parameter; and

a stationary noise generator that drives a synthesis filter with a random signal obtained from a random codebook, the synthesis filter comprising an LPC parameter obtained from the average decoded LSP parameter calculated in a period other than a period in which the mode determining apparatus determined to indicate the speech mode, and generates a stationary noise signal and superimposes the stationary noise signal over a decoded speech signal.

2. A speech decoding apparatus according to claim 1, wherein the mode determining apparatus comprises:

an average LSP calculator that calculates the average decoded LSP parameter;

a difference calculator that calculates differences between order components of the average decoded LSP parameter and corresponding order components of the decoded LSP parameter in the current frame, respectively; and

a first mode determiner that determines that the current frame indicates the speech mode when a difference greater than a predetermined level is calculated between at least one pair of order components.

3. A speech decoding apparatus according to claim 2, wherein the mode determining apparatus further comprises:

an inter-frame change calculator that calculates inter-frame changes in the decoded LSP parameter; and

a second mode determiner that determines that a period indicates the speech mode when the period shows an inter-frame change greater than a predetermined level, wherein;

the average LSP calculator deals with a period which is not the period determined by the second mode determiner to indicate the speech mode as the period in which the decoded LSP parameter is stationery;

the first mode determiner determines whether the period is not the period determined by the second mode determiner to indicate the speech mode; and

two step mode determination is performed by using the first mode determiner and the second mode determiner.

4. A speech decoding method comprising:

a decoding step of decoding a code representing a quantized LPC and generating a decoded LSP parameter for a current frame;

a mode determining step of calculating an average decoded LSP parameter in a period in which a decoded LSP parameter is stationary and determining whether the current frame indicates a speech mode or non-speech mode utilizing the average decoded LSP parameter; and

a stationary noise generating step of driving a synthesis filter with a random signal obtained from a random codebook, the synthesis filter comprising an LPC parameter obtained from the average decoded LSP parameter calculated in a period other than a period in which the mode determining step determined to indicate the speech mode, and generating a stationary noise signal and superimposing the stationary noise signal over a decoded speech signal.

5. A speech decoding method according to claim 4, wherein the mode determining step comprises:

an average LSP calculating step of calculating the average decoded LSP parameter;

a difference calculating step of calculating differences between order components of the average decoded LSP parameter and corresponding order components of the decoded LSP parameter in the current frame, respectively; and

a first mode determining step determining that the current frame indicates the speech mode when a difference greater than a predetermined level is calculated between at least one pair of order components.

6. A speech decoding method according to claim 5, wherein the mode determining step further comprises:

an inter-frame change calculating step of calculating inter-frame changes in the decoded LSP parameter; and

a second mode determining step of determining that a period indicates the speech mode when the period shows an inter-frame change greater than a predetermined level, wherein;

the average LSP calculating step of dealing with a period which is not the period determined by the second mode determiner to indicate the speech mode as a period in which the decoded LSP parameter is stationery;

the first mode determining step of determining whether the period is not the period determined by the second mode determining step to indicate the speech mode; and

two step mode determination is performed by using the first mode determining step and the second mode determining step.