A quantization apparatus for quantizing immittance spectral frequency, ISF, coefficients or line spectral frequency, LSF coefficients of an audio signal comprising: a first quantization module for performing quantization without an inter-frame prediction; a second quantization module for performing quantization with an inter-frame prediction; and a selection unit for selecting, in an open-loop manner, one of the first quantization module and the second quantization module, wherein the first quantization module comprises: a first quantization part for quantizing an input signal; and a third quantization part for quantizing a first quantization error signal, the second quantization module comprises: a second quantization part for quantizing a prediction error; and a fourth quantization part for quantizing a second quantization error signal, and the first quantization part and the second quantization part comprise a trellis structured vector quantizer, wherein the third quantization part and the fourth quantization part share a codebook and wherein a predetermined scaling is performed on a signal to be input to the third quantization part or the fourth quantization part, wherein the selection unit is configured to select the first quantization module if the prediction error is greater than a predetermined threshold. a first quantization module for performing quantization without an inter-frame prediction; a second quantization module for performing quantization with an inter-frame prediction; and a selection unit for selecting, in an open-loop manner, one of the first quantization module and the second quantization module, wherein the first quantization module comprises: a first quantization part for quantizing an input signal; and a third quantization part for quantizing a first quantization error signal, the second quantization module comprises: a second quantization part for quantizing a prediction error; and a fourth quantization part for quantizing a second quantization error signal, and the first quantization part and the second quantization part comprise a trellis structured vector quantizer, wherein the third quantization part and the fourth quantization part share a codebook and wherein a predetermined scaling is performed on a signal to be input to the third quantization part or the fourth quantization part, wherein the selection unit is configured to select the first quantization module if the prediction error is greater than a predetermined threshold. a first quantization part for quantizing an input signal; and a third quantization part for quantizing a first quantization error signal, the second quantization module comprises: a second quantization part for quantizing a prediction error; and a fourth quantization part for quantizing a second quantization error signal, and the first quantization part and the second quantization part comprise a trellis structured vector quantizer, wherein the third quantization part and the fourth quantization part share a codebook and wherein a predetermined scaling is performed on a signal to be input to the third quantization part or the fourth quantization part, wherein the selection unit is configured to select the first quantization module if the prediction error is greater than a predetermined threshold. a second quantization part for quantizing a prediction error; and a fourth quantization part for quantizing a second quantization error signal, and the first quantization part and the second quantization part comprise a trellis structured vector quantizer, wherein the third quantization part and the fourth quantization part share a codebook and wherein a predetermined scaling is performed on a signal to be input to the third quantization part or the fourth quantization part, wherein the selection unit is configured to select the first quantization module if the prediction error is greater than a predetermined threshold.