1. Field of the Invention
The present invention relates to an audio coding device and a method thereof by which an input audio signal is coded according to so-called transform coding and an obtained code string is transferred or recorded onto a recording medium, and also relates to an audio decoding device and a method thereof by which a code string transferred or red from a recording medium is decoded to obtain an output audio signal.
2. Description of the Related Art
There has been a known method in which spectrums obtained by performing time-frequency transform on an input audio signal are subjected to normalization/quantization and differential frequency spectrums as quantization errors are subjected again to normalization/quantization (see Patent Documents 1 and 2: Japanese Patent Publications No. 3227945 and No. 3227948). Quantization accuracy of the audio coding device can be improved by this method, and scalability can be realized to fit performance and use environment of the audio decoding device.