High-band encoding method and device, and high-band decoding method and device

A method for decoding an audio signal, the method comprising:

• generating an envelope of a low band of a spectrum based on a sub-band configuration of a full band, and quantizing the envelope of the low band;
• generating an envelope of a high band of the spectrum based on a sub-band configuration of the high band and quantizing the envelope of the high band;
• generating a mapped envelope of the high band by mapping the envelope of the high band into a sub-band configuration of the full band, and quantizing the mapped envelope;
• generating an envelope of the full band by combining the quantized mapped envelope of the high band with the quantized envelope of the low band;
• determining to perform envelope update if there is any sub-band to which a bit is allocated in the high band based on bit allocation information of the envelope of the full band;
• and
• in response to determining to perform the envelope update, decoding a delta of norm which is a difference between the mapped envelope and an envelope from an original spectrum for the sub-band to which the bit is allocated in the high band, and updating the envelope by using the delta of norm.

An apparatus for encoding an audio signal, the apparatus comprising:

• at least one processor configured to:
• generate an envelope of a low band of a spectrum based on a sub-band configuration of a full band, and quantize the envelope of the low band;
• generate an envelope of a high band of the spectrum based on a sub-band configuration of the high band and quantize the envelope of the high band;
• generate a mapped envelope of the high band by mapping the envelope of the high band into thea sub-band configuration of the full band, and quantize the mapped envelope;
• generate an envelope of the full band by combining the quantized mapped envelope of the high band with the quantized envelope of the low band;
• determine to perform envelope refinement if there is any sub-band to which a bit is allocated in the high band based on bit allocation information of the envelope of the full band;
• and
• in response to determining to perform the envelope refinement, calculate a delta of norm which is a difference between the mapped envelope and an envelope from an original spectrum for the sub-band to which the bit is allocated in the high band, and generate a bitstream including the delta of norm.

An apparatus for decoding an audio signal, the apparatus comprising:

• at least one processor configured to:
• generate an envelope of a low band of a spectrum based on a sub-band configuration of a full band, and quantize the envelope of the low band;
• generate an envelope of a high band of the spectrum based on a sub-band configuration of the high band, and quantize the envelope of the high band;
• generate a mapped envelope of the high band by mapping the envelope of the high band into a sub-band configuration of the full band, and quantize the mapped envelope;
• generate an envelope of the full band by combining the quantized mapped envelope of the high band with the quantized envelope of the low band;
• determine to perform envelope update if there is any sub-band to which a bit is allocated in the high band based on bit allocation information of the envelope of the full band;
• and
• in response to determining to perform the envelope update, decode a delta of norm which is a difference between the mapped envelope and an envelope from an original spectrum for the sub-band to which the bit is allocated in the high band, and update the envelope by using the delta of norm.