An audio/speech encoding apparatus comprising: a transformation section configured to transform the time domain input signal to frequency domain signal; a band splitting section configured to split the frequency domain signal to a plural of sub bands; a norm factor computation section configured to derive norm factors which represent the level of energies for each sub band; a quantization section configured to quantize the norm factors and further configured to determine quantization indices; a psychoacoustic modelling section configured to derive a masking threshold for each sub band; a modification of index section configured to modify the quantization indices, wherein the modification of index section further comprises: an energy computation section configured to compute the energies for each sub band, and a search section configured to identify the sub bands whose quantization error energy is below the derived masking threshold, and the modification of index section is configured to modify the indices of the identified sub bands by decreasing the indices value to be close to their neighboring sub band indices while the quantization error energy for the modified indices is below the derived masking threshold; a Huffman table selection section configured to select a Huffman table from among a number of predefined Huffman tables; a Huffman coding section configured to encode the indices using the selected Huffman table, wherein the Huffman coding section further comprises: a differential index calculation section configured to calculate differential indices between the current sub band and the previous sub band, and the Huffman coding section is configured to encode the differential indices; and a flag signal transmission section configured to transmit the flag signal to indicate the selected Huffman table. a transformation section configured to transform the time domain input signal to frequency domain signal; a band splitting section configured to split the frequency domain signal to a plural of sub bands; a norm factor computation section configured to derive norm factors which represent the level of energies for each sub band; a quantization section configured to quantize the norm factors and further configured to determine quantization indices; a psychoacoustic modelling section configured to derive a masking threshold for each sub band; a modification of index section configured to modify the quantization indices, wherein the modification of index section further comprises: an energy computation section configured to compute the energies for each sub band, and a search section configured to identify the sub bands whose quantization error energy is below the derived masking threshold, and an energy computation section configured to compute the energies for each sub band, and a search section configured to identify the sub bands whose quantization error energy is below the derived masking threshold, and the modification of index section is configured to modify the indices of the identified sub bands by decreasing the indices value to be close to their neighboring sub band indices while the quantization error energy for the modified indices is below the derived masking threshold; a Huffman table selection section configured to select a Huffman table from among a number of predefined Huffman tables; a Huffman coding section configured to encode the indices using the selected Huffman table, wherein the Huffman coding section further comprises: a differential index calculation section configured to calculate differential indices between the current sub band and the previous sub band, and a differential index calculation section configured to calculate differential indices between the current sub band and the previous sub band, and the Huffman coding section is configured to encode the differential indices; and a flag signal transmission section configured to transmit the flag signal to indicate the selected Huffman table.