Audio decoding apparatus and method for band expansion with aliasing adjustment
First Claim
1. 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 remover operable to adjust 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
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.
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Abstract
An audio decoding apparatus decodes high frequency component signals using a band expander that generates multiple high frequency subband signals from low frequency subband signals divided into multiple subbands and transmitted high frequency encoded information. The apparatus is provided with an aliasing detector and an aliasing remover. The aliasing detector detects the degree of occurrence of aliasing components in the multiple high frequency subband signals generated by the band expander. The aliasing remover suppresses aliasing components in the high frequency subband signals by adjusting the gain used to generate the high frequency subband signals. Thus occurrence of aliasing can be suppressed and the resulting degradation in sound quality can be reduced, even when real-valued subband signals are used in order to reduce the number of operations.
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Citations
30 Claims
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1. An audio decoding apparatus for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, said apparatus comprising:
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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 remover operable to adjust 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 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.
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2. An audio decoding apparatus for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, said apparatus comprising:
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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. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An audio decoding method for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, said method comprising:
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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. - View Dependent Claims (16)
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17. An audio decoding method for decoding a wideband audio signal from a bitstream containing encoded information for a narrowband audio signal, said method comprising:
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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. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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Specification