Patent ID: 8081764
Filing Date: 2011-12-20
Classification: G10L

Abstract:
1. An audio decoder which decodes a bitstream to generate audio signals of N channels, where N is equal to or larger than 2, the bitstream including a first coded data and a second coded data, the first coded data being generated by coding a down-mixed signal obtained by down-mixing the audio signals of the N channels, and the second coded data being generated by coding a parameter to be used to restore the down-mixed signals into original audio signals of the N channels, said audio decoder comprising: a frequency band signal generation unit operable to generate a first frequency band signal from the first coded data, the first frequency band signal corresponding to the down-mixed signal, and the first frequency band signal being expressed by a real number, regarding at least a part of frequency bands of the first frequency band signals; a channel expansion unit operable to convert the first frequency band signal into second frequency band signals using the second coded data, the first frequency band signal being generated by said frequency band signal generation unit, and the second frequency band signals corresponding to the respective audio signals of the N channels; a band synthesis unit operable to perform band synthesis for the second frequency band signals of the N channels which are generated by said channel expansion unit, thereby converting the second frequency band signals into the audio signals of the N channels, the audio signals being expressed on a time axis; and an aliasing noise detection unit operable to detect occurrence of an aliasing noise in the first frequency band signal, the aliasing noise resulting from that the first frequency band signal is expressed by the real number, wherein said aliasing noise detection unit is operable to detect a frequency band regarding the first frequency band signal, the frequency band having a signal with a high tonality where a signal level of a frequency component is maintained strong, the second coded data is data generated by coding a spatial parameter which includes a level ratio and a phase difference between the original audio signals of the N channels, and said channel expansion unit includes an adjustment module operable to adjust the signal level by adjusting an arithmetic coefficient generated from the spatial parameter, regarding a frequency band adjacent to the frequency band detected by said aliasing noise detection unit, wherein said channel expansion unit is operable to suppress the aliasing noise from being included in the second frequency band signals, by (i) generating the second frequency band signal, by mixing the first frequency band signal and a decorrelated signal by a ratio, the decorrelated signal being generated from the first frequency band signal, and the ratio corresponding to the arithmetic coefficient generated from the spatial parameter, and (ii) outputting the second frequency band signal in which a signal level is adjusted by said adjustment module.