Method for quantizing line spectral frequencies

An apparatus for decoding a plurality of indices representing a quantized audio parameter vector for an audio decoder, wherein the quantized audio parameter vector comprises a first plurality of quantized audio parameter coefficients, wherein the plurality of quantized audio parameter coefficients constitutes the order of the quantized audio parameter vector, wherein the apparatus comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:

• convert a first index of the plurality of indices using a codebook of a first quantizer to give a quantized first sub vector comprising a second plurality of quantized audio parameter coefficients;
• convert a second index of the plurality of indices using a codebook of a second vector quantizer to give a quantized second sub vector comprising a third plurality of quantized audio parameter coefficients, wherein the third plurality is a greater number than the second plurality and less than the first plurality;
• combine the quantized second sub vector and the quantized first sub vector to give a quantized audio parameter sub vector comprising a third plurality of quantized audio parameter coefficients;
• and
• predict at least one audio parameter coefficient for thea quantized audio parameter vector using the third plurality of quantized audio parameter coefficients, wherein the at least one audio parameter coefficient is a higher order audio parameter coefficient than an order of the quantized audio parameter sub vector.

A method for quantizing an audio parameter vector for an audio encoder, wherein the audio parameter vector comprises a first plurality of audio parameter coefficients, wherein the first plurality of audio parameter coefficients constitutes the order of the of the audio parameter vector, wherein the method comprises:

• determining a first sub vector comprising a second plurality of audio parameter coefficients of the audio parameter vector, wherein the second plurality is less than the first plurality;
• quantizing the first sub vector with a first quantizer to give a quantized first sub vector;
• determining a residual vector as a second sub vector comprising a third plurality of coefficients by subtracting the quantized first sub vector from the audio parameter vector, wherein the third plurality is a greater number than the second plurality and less than the first plurality;
• quantizing the second sub vector with a second quantizer to give a quantized second sub vector;
• combining the quantized second sub vector and the quantized first sub vector to give a quantized audio parameter sub vector comprising a third plurality of quantized audio parameter coefficients;
• and
• predicting at least one audio parameter coefficient for a quantized audio parameter vector using the third plurality of quantized audio parameter coefficients, wherein the at least one audio parameter coefficient is a higher order audio parameter coefficient than an order of the of quantized audio parameter sub vector.

A method for decoding a plurality of indices representing a quantized audio parameter vector for an audio decoder, wherein the quantized audio parameter vector comprises a first plurality of quantized audio parameter coefficients, wherein the first plurality of quantized audio parameter coefficients constitutes the order of the quantized audio parameter vector, wherein the method comprises:

• converting a first index of the plurality of indices using a codebook of a first quantizer to give a quantized first sub vector comprising a second plurality of quantized audio parameter coefficients;
• converting a second index of the plurality of indices using a codebook of a second vector quantizer to give a quantized second sub vector comprising a third plurality of quantized audio parameter coefficients, wherein the third plurality is a greater number than the second plurality and less than the first plurality;
• combining the quantized second sub vector and the quantized first sub vector to give a quantized audio parameter sub vector comprising a third plurality of quantized audio parameter coefficients;
• and
• predicting at least one audio parameter coefficient for the quantized audio parameter vector using the third plurality of quantized audio parameter coefficients, wherein the at least one audio parameter coefficient is a higher order audio parameter coefficient than an order of the quantized audio parameter sub vector.