Embedded code-excited linear prediction speech coding and decoding apparatus and method

A speech decoding apparatus comprising:

• an excitation signal reproduction unit which reconstructs a basic excitation signal using an adaptive codebook index and gain, and an algebraic codebook index and gain of a core speech coder;
• an embedded excitation signal reproduction unit for decoding a residual excitation signal from a bit stream added in an embedded type according to a determination made by an embedded coder as to which one of a multiple pulse excitation coding method and a gain compensation method is optimal for coding the residual excitation signal, that is not coded in the core speech coding unit, with the additionally allowed bits;
• and
• a linear prediction synthesis filter unit which reconstructs a speech signal by performing a linear prediction synthesis of the reconstructed basic excitation signal at the excitation signal reproduction unit and the decoded residual excitation signal at the embedded excitation signal reproduction unit,
• wherein the gain compensation method derives a gain compensation value for compensating a gain obtained from an algebraic codebook search, the gain compensation value being multiplied with the gain obtained from the algebraic codebook search to update the gain, and
• wherein the embedded coder selects a position and a sign of multiple pulses that minimize a square error εm of the residual excitation signal, determines the gain compensation value that minimizes a square error εg of the residual excitation signal, compares εm with εg, selects the multiple pulse excitation coding method when εm<εg, and selects the gain compensation method when εm>εg.

A speech coding method comprising the steps of:

• a) presenting, by a speech coding apparatus, a speech signal with an excitation signal;
• b) allocating, by the speech coding apparatus, the number of bits that are additionally allowed due to a capacity change in a transmission channel;
• and
• c) determining, by the speech coding apparatus, which one of a multiple pulse excitation coding method and a gain compensation method is optimal for coding a residual excitation signal, that is not coded in the core speech coding unit, with the additionally allowed bits, and generating the residual excitation signal coded by the determined method,
• wherein the gain compensation method derives a gain compensation value for compensating a gain obtained from an algebraic codebook search, the gain compensation value being multiplied with the gain obtained from the algebraic codebook search to update the gain,
• wherein the step c) comprises:
• c1) calculating the residual excitation signal,
• c2) determining a pulse position and a sign which minimize a square error εm of the residual excitation signal;
• c3) determining the gain compensation value which minimizes a square error εg of the residual excitation signal;
• and
• c4) comparing εm with εg, selecting the multiple pulse excitation coding method when εm<εg, and selecting the gain compensation method when εm>εg.

A speech decoding method comprising the steps of:

• a) reconstructing, by a speech decoding apparatus, a basic excitation signal using an adaptive codebook index and gain, and an algebraic codebook index and gain of a speech coder;
• b) decoding, by the speech decoding apparatus, a residual excitation signal from a bit stream added in an embedded type according to a determination made by an embedded coder as to which one of a multiple pulse excitation coding method and a gain compensation method is optimal for coding the residual excitation signal, that is not coded in the core speech coding unit, with the additionally allowed bits;
• and
• c) reconstructing, by the speech decoding apparatus, a speech signal by performing a linear prediction synthesis of the reconstructed basic excitation signal and the decoded residual excitation signal,
• wherein the gain compensation method derives a gain compensation value for compensating a gain obtained from an algebraic codebook search, the gain compensation value being multiplied with the gain obtained from the algebraic codebook search to update the gain,
• wherein the embedded coder selects a position and a sign of multiple pulses that minimize a square error εm of the residual excitation signal, determines the gain compensation value that minimizes a square error εg of the residual excitation signal, compares εm with εg, selects the multiple pulse excitation coding method when εm<εg, and selects the gain compensation method when εm>εg.