Device and method for bandwidth extension for audio signals

An audio signal decoding apparatus comprising:

• a demultiplexing section that demultiplexes low-band encoding parameters, index information, and scale factor information from encoded information transmitted from an encoding apparatus that encodes an audio signal;
• a low-band decoding section that decodes the low-band encoding parameters to obtain a synthesized low frequency spectrum;
• a spectrum replication section that replicates a high frequency subband spectrum based on the index information using the synthesized low frequency spectrum;
• and
• a spectrum envelope adjustment section that adjusts an amplitude of the replicated high frequency subband spectrum using the scale factor information,
• a harmonic frequency estimation section that estimates a frequency of a harmonic component in the synthesized low frequency spectrum;
• a harmonic frequency adjustment section that adjusts a frequency of a harmonic component in the high frequency subband spectrum using the estimated harmonic frequency spectrum;
• and
• an output section that generates an output signal using the synthesized low frequency spectrum and the high frequency subband spectrum.

An audio signal encoding apparatus comprising:

• a low-band encoding section that encodes a low frequency audio signal and outputs synthesized low frequency spectrum, and generates low-bandparameters and outputs the parameters;
• a subband split section that transforms a high frequency audio signal to a frequency spectrum and split a high frequency spectrum into a plurality of subbands (hereinafter, high frequency subbands), the high frequency spectrum being obtained using time-frequency transformed an input audio signal;
• a search section that identifies the most correlated portion from the synthesized low frequency spectrum for each of the high frequency subbands and outputs the identification result as index information;
• a scale factor estimation section that estimates an energy scale factor between each of the high frequency subbands and the most correlated portion identified from the synthesized low frequency spectrum and outputs the scale factor as scale factor information;
• a harmonic frequency estimation section that estimates and outputs a harmonic frequency of the synthesized low frequency spectrum and a harmonic frequency of the transformed input audio signal;
• and
• a multiplex section that multiplexes the low-band parameter, the index information, and the scale factor information.

An audio signal decoding method, comprising:

• demultiplexing low-band encoding parameters, index information, and scale factor information from encoded information transmitted from an encoding apparatus that encodes an audio signal;
• decoding the low-band encoding parameters to obtain a synthesized low frequency spectrum;
• replicating a high frequency subband spectrum based on the index information using the synthesized low frequency spectrum;
• and
• adjusting an amplitude of the replicated high frequency subband spectrum using the scale factor information,
• estimating a frequency of a harmonic component in the synthesized low frequency spectrum;
• adjusting a frequency of a harmonic component in the high frequency subband spectrum using the estimated harmonic frequency spectrum;
• and
• generating an output signal using the synthesized low frequency spectrum and the high frequency subband spectrum.

An audio signal encoding apparatus comprising:

• encoding a low frequency audio signal and outputs synthesized low frequency spectrum, and generates low-bandparameters and outputs the parameters;
• transforming a high frequency audio signal to a frequency spectrum;
• splitting a high frequency spectrum into a plurality of subbands (hereinafter, high frequency subbands), the high frequency spectrum being obtained using time-frequency transformed an input audio signal;
• identifying the most correlated portion from the synthesized low frequency spectrum for each of the high frequency subbands;
• outputting the identification result as index information;
• estimating an energy scale factor between each of the high frequency subbands and the most correlated portion identified from the synthesized low frequency spectrum and outputs the scale factor as scale factor information;
• estimating a harmonic frequency of the synthesized low frequency spectrum and a harmonic frequency of the transformed input audio signal;
• and
• multiplexing the low-band parameter, the index information, and the scale factor information.