Data processing: speech signal processing – linguistics – language – Audio signal bandwidth compression or expansion – With content reduction encoding
Reexamination Certificate
1999-06-07
2002-09-10
Banks-Harold, Marsha D. (Department: 2654)
Data processing: speech signal processing, linguistics, language
Audio signal bandwidth compression or expansion
With content reduction encoding
C704S503000
Reexamination Certificate
active
06449596
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a wide band audio signal encoding apparatus, a wide band audio signal encoding and decoding apparatus, and a wide band audio signal recording medium for transmitting a digital signal with high quality and almost no deterioration.
BACKGROUND ART
Conventionally, recording and reproduction of instrumental and vocal sounds have been widely executed using digital signals of a compact disc (CD), digital data recorder (DAT) and so on. For example, sounds are recorded on the compact disc using a linear coding recording method having a sampling frequency of 44.1 kHz and a number of bits for quantization of 16 bits. According to this method, it is theoretically impossible to reproduce a sound exceeding 22.05 kHz and obtain a dynamic range exceeding 98 dB. That is, although an acoustic signal generated through a live instrumental performance contains a frequency component exceeding 22.05 kHz, it has been considered unnecessary to reproduce these frequency components for the reason that these frequency components are out of the audible band.
However, research has been conducted into the possibility that an ultrahigh frequency sound activates the alpha wave, or a brain wave of the human being, and it has started to be considered that the ultrahigh frequency sound produces some effect on the brain wave. Although it cannot be indiscriminately decided whether or not the ultrahigh frequency sound can be heard by the human being also depending on individual differences, it is pointed out that the ultrahigh frequency sound has some physical and physiological influences and effects and that the ultrahigh frequency sound component in a reproduced signal is important for the purpose of leaving sounds of higher qualities as a cultural inheritance for the future.
Furthermore, with regard to the fact that the actual instrumental sounds have a dynamic range that exceeds 100 dB and sometimes reaches 130 dB, it is pointed that there is a shortage of dynamic range due to the fact that a clipping distortion tends to occur when the sounds are expressed by 16 bits in quantization and the fact that a distortion due to a quantization error, particularly in a region where the signal is small, causes a sound impurity.
In view of the above, there has been proposed a first prior art method, as disclosed in a first prior art reference, “Hirohiko Kamigahira, “Manufacturer's Strategies for the Next-Generation High-quality CD”, Musen to Jikken, published by Seibundou Shinkousha, Vol. 82, No. 2, pp. 100-107, February, 1995“, in which the least significant bit LSB of 16-bit data is used and music signal information not lower than 22.05 kHz is recorded by ADPCM (Adaptive Differential Pulse Code Modulation) in this least significant bit LSB. There has also been proposed a second prior art method, as disclosed in a second prior art reference, “Makoto Akune et al., “Theory and Operation of Super Bit Mapping”, published by Radio Gijutsu, Radio Gijutsusha, Vol. 1, 45, No. 4, pp. 146-150, April, 1991“, in which the quantization noise is moved into a frequency range of 15 kHz to 22.05 kHz by a noise shaping process, thereby improving the dynamic range in terms of auditory sensation.
As a next-generation format, there is a SD (Super Density Disk) format studied as a fundamental technique of DVD (Digital Video Disk or Digital Versatile Disk) as a consequence of the recent development of the practicability of a high-density recording disk. In regard to the audio section of the SD format, the summary thereof is announced in a third prior art reference, “Hidehiro Ishii et al., “The Application of a New High-Density Optical Disc for Audio”, Proceedings of The 99th Convention of an Audio Engineering Society, 4121(D-9), New York, Oct. 6-9, 1995“, which discloses a linear PCM system with a sampling frequency of 48 kHz and 16 bits for quantization, as well as the specifications of the proposed SD format that remarkably exceeds the specifications of the prior art CD as exemplified by a linear PCM system with a sampling frequency of 96 kHz and 24 bits for quantization. This proposed format provides the prospects for the achievement of a reproduction frequency band of about 45 kHz and a dynamic range of 140 dB.
However, as disclosed in the recent research paper, as a fourth prior art reference, “Tsutomu OOhashi et al., “A study on the difference of the sound quality between LP sound and CD sound—Physiological and KANSEI(Sensory) Scientific Approach”, Technical Report of The Institute of Electronics, Information and Communication Engineers, HC94-06, pp. 15-22, June, 1994“, it is confirmed that a signal that exceeds 50 kHz and reaches 100 kHz is recorded in a reproducible state on the LP (Long-Playing) record, and particularly in a fortissimo part of the ethnic instrument of a gamelan, a spectrum that exceeds 50 kHz and reaches 100 kHz is observed.
From this result of research, it cannot help but be said that even the band of about 45 kHz of the proposed SD format is still insufficient for faithfully reproducing such music. The reproduction band is also extended beyond 100 kHz if the sampling frequency of the SD format is further increased to, for example, 240 kHz. However, the amount of information necessary for it is 5.76 Mbps per channel, and this amounts to a vast amount of information of 11.52 Mbps in a 2-channel stereo system. This has consequently led to the problem that the sound can be recorded for up to only about 50 minutes even when DVD having a recording capacity of 4.7 gigabytes is used and it exceeds the upper limit of 6.75 Mbps of the bit rate temporary allocation, resulting in an impracticability.
A first object of the present invention is to solve the above-mentioned problems and to provide a wide band audio signal encoding apparatus capable of encoding an audio signal in a wider band with a higher dynamic range as compared with those of the prior art.
A second object of the present invention is to provide a wide band audio signal decoding apparatus capable of decoding an audio signal in a wider band with a larger dynamic range as compared with those of the prior art.
A third object of the present invention is to provide a wide band audio signal encoding and decoding apparatus capable of encoding and decoding an audio signal in a wider band with a larger dynamic range as compared with those of the prior art.
A fourth object of the present invention is to provide a wide band audio recording medium capable of recording an audio signal in a wider band with a larger dynamic range as compared with those of the prior art.
SUMMARY OF THE INVENTION
In order to achieve the above-mentioned objective, according to a first aspect of the present invention, there is provided a wide band audio signal encoding apparatus comprising a sub-band dividing filter for dividing inputted wide band audio data into signal data of a predetermined natural number N of sub-bands, and outputting the resulting data, N sub-sampling means for sub-sampling the signal data of the N sub-bands outputted from the sub-band dividing filter with respective predetermined numbers of bits for quantization, respectively, and outputting the resulting data, encoding system controlling means for determining the numbers of bits for quantization of said N sub-sampling means based on inputted noise floor information and setting the determined numbers of bits for quantization to the respective N sub-sampling means, respectively, and a multiplexer for multiplexing the signal data of the N sub-bands outputted from the N sub-sampling means, and outputting the multiplexed encoded data.
Also, according to a second aspect of the present invention, there is provided a wide band audio signal encoding apparatus comprising encoding system controlling means for determining a bandwidth of division and a number N of division of bands of the wide band audio data based on inputted signal information including signal band information of inputted wide band audio data, a sub-band dividing filter for dividing the wide band audio data into sig
Banks-Harold Marsha D.
Storm Donald L.
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