Audio decoding apparatus and method for band expansion with aliasing adjustment

An audio decoding apparatus for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, said apparatus comprising:

• a bitstream demultiplexer operable to demultiplex the encoded information from the bitstream;
• a decoder operable to decode the narrowband audio signal from the demultiplexed encoded information;
• an analysis filter bank operable to divide the decoded narrowband audio signal into multiple subband signals composing a first subband signal having a frequency band;
• a band expander operable to generate a second subband signal from the first subband signal, the second subband signal being composed of multiple subband signals each having a higher frequency band than the frequency band of the first subband signal;
• an aliasing detector operable to detect a degree of aliasing in the subband signals of the second subband signal generated by the band expander;
• an aliasing remover operable to adjust a gain of the subband signals of the second subband signal based on the degree of aliasing detected by the aliasing detector;
• and
• a real-valued calculation synthesis filter bank operable to synthesize the first subband signal and the second subband signal to obtain the wideband audio signal.

An audio decoding method for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, said method comprising:

• demultiplexing the encoded information from the bitstream;
• decoding the narrowband audio signal from the demultiplexed encoded information;
• dividing the decoded narrowband audio signal into multiple subband signals composing a first subband signal having a frequency band;
• generating a second subband signal from the first subband signal, the second subband signal being composed of multiple subband signals each having a higher frequency band than the frequency band of the first subband signal;
• adjusting a gain based on a degree of aliasing in the subband signals of the second subband signal so as to suppress aliasing components occurring in the subband signals of the second subband signal;
• and
• synthesizing the first subband signal and the second subband signal using a real-valued filtering calculation to obtain the wideband audio signal.

An audio decoding method for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, said method comprising:

• demultiplexing the encoded information from the bitstream;
• decoding the narrowband audio signal from the demultiplexed encoded information;
• dividing the decoded narrowband audio signal into multiple subband signals composing a first subband signal having a frequency band;
• generating a second subband signal from the first subband signal, the second subband signal being composed of multiple subband signals each having a higher frequency band than the frequency band of the first subband signal;
• detecting a degree of aliasing in each of the generated multiple subband signals of the second subband signal before the second subband signal is generated;
• adjusting a gain of the subband signals of the second subband signal based on the degrees of aliasing detected;
• and
• synthesizing the first subband signal and the second subband signal using a real-valued filtering calculation to obtain the wideband audio signal.