Encoding device and decoding device

#The present invention relates to encoding methods for compressing data by encoding signals obtained by transforming audio signals such sound and music signals in the time domain into those in the frequency domain with a smaller amount of encoded data stream, using a method such as an orthogonal transform, and decoding methods for expanding the data upon receipt of the encoded data stream and obtaining the audio signals.

#A number of methods of encoding and decoding audio signals have been developed up to now. Particularly, in these days, IS13818-7, which is internationally standardized in ISO/IEC, is publicly known and highly appreciated as an encoding method for reproducing high quality sound with high efficiency. This encoding method is called Advanced Audio Coding (AAC). In recent years, the AAC is adopted to the standardization called MPEG 4, and a system called MPEG-4 AAC that has some extended functions added to the IS13818-7 has been developed. An example of the encoding procedure is described in the informative part of the MPEG-4 AAC.

#The following is an explanation for an audio encoding device using the conventional encoding method referring to FIG. 1. FIG. 1 is a block diagram that shows the structure of a conventional encoding device 100. The encoding device 100 includes a time-frequency transforming unit 101, a spectrum amplifying unit 102, a spectrum quantizing unit 103, a Huffman coding unit 104 and an encoded data stream transfer unit 105. A digital audio signal on the time axis obtained by sampling an analog audio signal at a predetermined frequency is divided into every predetermined number of samples at a predetermined time interval, transformed into data on the frequency axis through the time-frequency transforming unit 101, and then given to the spectrum amplifying unit 102 as an input signal into the encoding device 100. The spectrum amplifying unit 102 amplifies a spectrum included in every predetermined band with one certain gain. The spectrum quantizing unit 103 quantizes the amplified spectrum with a predetermined transform expression. In the case of AAC method, the quantization is conducted by rounding off frequency spectral data, which is expressed in floating points into an integer value. The Huffman coding unit 104 encodes the quantized spectral data in a set of certain pieces thereof according to Huffman coding, and encodes the gain in every predetermined band in the spectrum amplifying unit 102 and the data that specifies the transform expression for the quantization according to Huffman coding, and then transmits the codes of them to the encoded data stream transfer unit 105. The Huffman-coded data stream is transferred from the encoded data stream transfer unit 105 to a decoding device via a transmission channel or a recording medium, and reconstructed as an audio signal on the time axis by the decoding device. The conventional encoding device operates as described above.

#The encoding devices and the decoding devices according to the embodiments of the present invention will be explained with reference to figures (FIG. 2-FIG. 20).

#(First Embodiment)

#FIG. 2 is a block diagram showing the structure of an encoding device 200 according to the first embodiment of the present invention. The encoding device 200 is an encoding device that extracts a time characteristic of an audio input signal expressed on a time axis and encodes after partially transforming a part of a frequency spectrum into a frequency signal in a time domain based on the extracted time characteristic, which includes a time-frequency transforming unit 201, a frequency characteristic extracting unit 202, a time characteristic extracting unit 203, a time transforming unit 204 and an encoded data stream generating unit 205.