Sound encoder and sound encoding method for generating a second layer decoded signal based on a degree of variation in a first layer decoded signal
First Claim
1. A speech coding apparatus that performs coding having a layered structure composed of a plurality of layers, the speech coding apparatus comprising:
- an analyzer, including a first circuit, that analyzes a spectrum of a decoded signal of a lower layer to calculate a decoded spectrum of the lower layer;
a selector, including a second circuit, that selects one nonlinear transform function from among a plurality of nonlinear transform functions based on a degree of variation of the decoded spectrum of the lower layer, the degree of variation being a standard deviation of the decoded spectrum of the lower layer;
an inverse transformer, including a third circuit, that inverse transforms a nonlinear transformed residual spectrum using the one nonlinear transform function selected by the selector to obtain an inverse transformed residual spectrum; and
an adder, including a fourth circuit, that adds the inverse transformed residual spectrum to the decoded spectrum of the lower layer to obtain a decoded spectrum of an upper layer.
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Abstract
A sound encoder having an improved quantization performance while suppressing an increase of the bit rate to a lowest level. In a second layer encoder, a standard deviation calculator calculates a standard deviation σc of a first layer decoding spectrum after decoding a scale factor ratio multiplication and outputs the standard deviation σc to a selector. The selector selects a linear transform function as a function for a nonlinear transform of a residual spectrum according to the standard deviation σc A nonlinear transform function selects one of prepared nonlinear transform functions #1 to #N according to a result of the selection by the selector, and outputs the selected one to an inverse transformer. The inverse transformer subjects an inverse transform (expansion) to a residual spectrum candidate that is stored in a residual spectrum code book using the nonlinear transform function outputted from the nonlinear transform function and outputs the result to an adder.
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Citations
20 Claims
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1. A speech coding apparatus that performs coding having a layered structure composed of a plurality of layers, the speech coding apparatus comprising:
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an analyzer, including a first circuit, that analyzes a spectrum of a decoded signal of a lower layer to calculate a decoded spectrum of the lower layer; a selector, including a second circuit, that selects one nonlinear transform function from among a plurality of nonlinear transform functions based on a degree of variation of the decoded spectrum of the lower layer, the degree of variation being a standard deviation of the decoded spectrum of the lower layer; an inverse transformer, including a third circuit, that inverse transforms a nonlinear transformed residual spectrum using the one nonlinear transform function selected by the selector to obtain an inverse transformed residual spectrum; and an adder, including a fourth circuit, that adds the inverse transformed residual spectrum to the decoded spectrum of the lower layer to obtain a decoded spectrum of an upper layer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A speech coding method implemented in at least one of at least one circuit and at least one processor for performing coding having a layered structure composed of a plurality of layers, the speech coding method comprising:
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analyzing, with the at least one of the at least one circuit and the at least one processor, a spectrum of a decoded signal of a lower layer to calculate a decoded spectrum of the lower layer; selecting, with the at least one of the at least one circuit and the at least one processor, one nonlinear transform function from among a plurality of nonlinear transform functions based on a degree of variation of the decoded spectrum of the lower layer, the degree of variation being a standard deviation of the decoded spectrum of the lower layer; inverse transforming, with the at least one of the at least one circuit and the at least one processor, a nonlinearly transformed residual spectrum using the one nonlinear transform function to obtain an inverse transformed residual spectrum; and adding, with the at least one of the at least one circuit and the at least one processor, the inverse transformed residual spectrum to the decoded spectrum of the lower layer to obtain a decoded spectrum of an upper layer. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification