Coding apparatus for digital signal
DC CAFCFirst Claim
1. An apparatus for compressing a digital input signal, the apparatus comprising:
- band division filter means for dividing the digital input signal in frequency into plural signals, each of the plural signals being in a respective one of plural frequency ranges, the plural signals including a frequency range signal in one of the plural frequency ranges;
block length decision means, operating in response to an index, for determining a division of the frequency range signal into blocks to provide a block length decision signal indicating a block length for each of the blocks;
block floating processing means, operating in response to the block length decision signal from the block length decision means and in response to the index, for applying block floating processing to the blocks of the frequency range signal, each of the blocks having the block length indicated by the block length decision signal, the block floating processing circuit providing a block of a block floating processed frequency range signal from each of the blocks of the frequency range signal;
orthogonal transform means for orthogonally transforming the block of the block floating processed frequency range signal to produce plural spectral coefficients; and
adaptive bit allocation means for dividing the plural spectral coefficients from the orthogonal transform means into bands and for adaptively allocating a number of quantizing bits to quantize the spectral coefficients in each of the bands in response to an allowable noise level in each of the bands.
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Abstract
In a coding apparatus for a digital signal adapted for implementing, every variable length block, floating processing to an input digital signal by using a block floating processing circuit thereafter to orthogonally transform signal components which have undergone such processing by using orthogonal transform circuits (e.g., DCT circuits), the block floating processing circuit is constructed so as to determine the length of a variable length block and a floating coefficient of the block floating processing on the basis of the same index, e.g., a maximum absolute value in that block. Thus, a quantity subject to processing can be reduced. In addition, there may be employed such a configuration to divide, every critical bands, spectrum signals on the frequency base from DCT (Discrete Cosine Transform) circuits to determine, every respective critical bands, allowed noises in which the masking is taken into consideration to compare these allowed noises and a minimum audible curve from a minimum audible curve generator at a comparator. When the minimum audible curve is grater than an allowed noise at that time, this minimum audible curve is considered as an allowed noise to divide the critical band into smaller bands to carry out bit allocation every respective smaller bands, and to rase or set a flag. Thus, an accurate allowed noise level can be provided without increasing auxiliary information.
38 Citations
68 Claims
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1. An apparatus for compressing a digital input signal, the apparatus comprising:
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band division filter means for dividing the digital input signal in frequency into plural signals, each of the plural signals being in a respective one of plural frequency ranges, the plural signals including a frequency range signal in one of the plural frequency ranges; block length decision means, operating in response to an index, for determining a division of the frequency range signal into blocks to provide a block length decision signal indicating a block length for each of the blocks; block floating processing means, operating in response to the block length decision signal from the block length decision means and in response to the index, for applying block floating processing to the blocks of the frequency range signal, each of the blocks having the block length indicated by the block length decision signal, the block floating processing circuit providing a block of a block floating processed frequency range signal from each of the blocks of the frequency range signal; orthogonal transform means for orthogonally transforming the block of the block floating processed frequency range signal to produce plural spectral coefficients; and adaptive bit allocation means for dividing the plural spectral coefficients from the orthogonal transform means into bands and for adaptively allocating a number of quantizing bits to quantize the spectral coefficients in each of the bands in response to an allowable noise level in each of the bands. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus for compressing a digital input signal, the apparatus comprising:
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band division filter means for dividing the digital input signal into plural signals, each of the plural signals being in a respective one of plural frequency ranges, the plural signals including a frequency range signal in one of the plural frequency ranges; block floating processing means for applying block floating processing to blocks of the frequency range signal to provide a block floating processed frequency range signal; orthogonal transform means for orthogonally transforming blocks of the block floating processed frequency range signal to provide plural spectral coefficients; and adaptive bit allocation means for dividing the spectral coefficients from the orthogonal transform means into bands and for adaptively allocating a number of quantizing bits for quantizing the spectral coefficients in each of the bands in response to an allowable noise level in each of the bands, the adaptive bit allocation means including; allowable noise level calculation means for calculating the allowable noise level for each of the bands, comparison means for comparing, in each of the bands, the allowable noise level with a minimum audible level and, for each of the bands in which the minimum audible level is higher than the allowable noise level, for setting a flag, and means for selecting, in each of the bands in which the flag is set, the minimum audible level as the allowable noise level. - View Dependent Claims (10, 11, 12, 13, 14)
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15. An apparatus for compressing a digital input signal, the apparatus comprising:
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index generating means for generating an index in response to the digital input signal; block length decision means for determining a division of the digital input signal into blocks in response to the index; block floating processing means for applying block floating processing to the blocks of the digital input signal in response to the index to provide block floating processed blocks of the digital input signal; orthogonal transform means for orthogonally transforming each of the block floating processed blocks of the digital input signal to produce plural spectral coefficients; and adaptive bit allocation means for dividing the plural spectral coefficients from the orthogonal transform means into bands, and for adaptively allocating a number of quantizing bits to quantize the spectral coefficients in each of the bands. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. An apparatus for compressing a digital input signal, the apparatus comprising:
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block length decision means for determining a division of the digital input signal into blocks in response to an index; block floating means for applying block floating processing to each of the blocks of the digital input signal using the index as a block floating coefficient; and means for deriving spectral coefficients from the block floating processed blocks of the digital input signal; and adaptive bit allocation means for dividing the spectral coefficients by frequency into bands and for adaptively allocating a number of quantizing bits for quantizing the spectral coefficients in each of the bands in response to an allowable noise level for each of the bands, the adaptive bit allocation means including; allowable noise level calculation means for calculating an allowable noise level for each of the bands, comparing means for comparing, in each of the bands, the allowable noise level with a minimum audible level, and selecting means for selecting the minimum audible level as the allowable noise level in each of the bands for which the comparing means determines that the minimum audible level is higher than the allowable noise level. - View Dependent Claims (26, 27, 28, 29, 30)
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31. A method for compressing a digital input signal, the method comprising the steps of:
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generating an index in response to the digital input signal; determining a division of the digital input signal into blocks in response to the index; applying block floating processing to the blocks of the digital input signal in response to the index to provide block floating processed blocks of the digital input signal; orthogonally transforming each of the block floating processed blocks of the digital input signal to produce plural spectral coefficients; and dividing the plural spectral coefficients into bands, and adaptively allocating a number of quantizing bits to quantize the spectral coefficients in each of the bands. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39, 40, 41)
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42. A method for compressing a digital input signal, the method comprising steps of:
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determining a division of the digital input signal into blocks in response to an index; applying block floating processing to each of the blocks of the digital input signal using the index as a block floating coefficient; deriving spectral coefficients from the block floating processed blocks of the digital input signal; dividing the spectral coefficients by frequency into bands; and adaptively allocating a number of quantizing bits for quantizing the spectral coefficients in each of the bands in response to an allowable noise level for each of the bands, the step of adaptively allocating a number of quantizing bits including steps of; calculating an allowable noise level for each of the bands, comparing, in each of the bands, the allowable noise level with a minimum audible level, and selecting the minimum audible level as the allowable noise level in each of the bands for which the step of comparing determines that the minimum audible level is higher than the allowable noise level. - View Dependent Claims (43, 44, 45, 46, 47, 48)
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49. An apparatus for expanding a compressed digital signal including plural quantized spectral coefficients and auxiliary information, the apparatus comprising:
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adaptive bit allocation decoding means, operating in response to the auxiliary information, for inversely quantizing the quantized spectral coefficients to provide plural spectral coefficients; block floating means for applying inverse block floating to the spectral coefficients to provide inverse block floating processed spectral coefficients; inverse orthogonal transform means for inversely orthogonally transforming the inverse block floating processed spectral coefficients to provide plural frequency range signals; and inverse filter means for synthesizing the frequency range signals to provide an output signal. - View Dependent Claims (50, 51)
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52. A method for expanding a compressed digital signal to provide a digital output signal, the compressed digital signal including:
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(a) plural quantized spectral coefficients divided by frequency into bands, the bands including a divided band in which the spectral coefficients therein are further divided by frequency into sub bands, the quantized spectral coefficients in each of the bands and each of the sub bands being quantized using an adaptively-allocated number of quantizing bits, (b) an allowable noise level for each band, and (c) a flag signal for the divided band, the method comprising the steps of; setting the allowable noise level of the divided band as the allowable noise level for the divided band when the flag signal for the divided band is in a first state, and setting the allowable noise level of the divided band as the allowable noise level for one of the sub bands constituting the divided band when the flag signal for the divided band is in a second state; determining, when the flag signal for the divided band is second state, from the allowable noise level of the divided band, an allowable noise level for each of the other ones of the sub bands constituting the divided band; using the allowable noise level for each of the bands and for each of the sub bands constituting the divided band to inversely quantize the respective quantized spectral coefficients in each of the bands and in each of the sub bands constituting the divided band to provide spectral coefficients; and deriving the digital output signal from the spectral coefficients. - View Dependent Claims (53, 54, 55, 56)
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57. An apparatus for compressing a digital input signal, the apparatus comprising:
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means for deriving spectral coefficients from the digital input signal; frequency dividing means for dividing the spectral coefficients by frequency into bands, the bands including a band corresponding to a critical band, and additionally for subdividing the spectral coefficients in the band by frequency into sub bands, the sub bands including a lowest-frequency sub band; allowable noise level calculation means for calculating a allowable noise level for each of the bands; supplying means for supplying a minimum audible level for each of the bands except the band, and for each of the sub bands in the band; comparing means for determining, in each of the bands except the band, when the minimum audible level supplied by the supplying means is greater than the allowable noise level calculated by the allowable noise level calculation means, and for determining, in the band, when the minimum audible level supplied by the supplying means for only the lowest-frequency sub band is greater than the allowable noise level calculated by the allowable noise level calculation means for the band; substituting means for substituting, in each one of the bands in which the comparing means determines that the minimum audible level is greater than the allowable noise level, the minimum audible level supplied by the supplying means for the allowable noise level calculated by the allowable noise level calculating means as the allowable noise level for the one of the bands, and for substituting, in each one of the sub bands in the band when the comparing means determines that the minimum audible level for the lowest-frequency sub band is greater than the allowable noise level for the band, the minimum audible level supplied for the one of the sub bands by the supplying means for the allowable noise level calculated for the band by the allowable noise level calculation means as the allowable noise level for the one of the sub bands; and adaptive bit allocation means for adaptively allocating a number of quantizing bits among the bands and the sub bands for quantizing the spectral coefficients therein, the bit allocation means allocating quantizing bits among the bands and the sub bands in response to the allowable noise level for each of the bands and sub bands. - View Dependent Claims (58, 59, 60, 61, 62)
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63. A method for compressing a digital input signal, the method comprising steps of:
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deriving spectral coefficients from the digital input signal; dividing the spectral coefficients by frequency into bands, the bands including a band corresponding to a critical band; subdividing the spectral coefficients in the band by frequency into sub bands, the sub bands including a lowest-frequency sub band; calculating an allowable noise level for each of the bands; supplying a minimum audible level for each of the bands except the band, and for each of the sub bands in the band; determining, in each of the bands except the band, when the minimum audible level supplied in the supplying step is greater than the allowable noise level calculated in the allowable noise level calculating step, and determining, in the band, when the minimum audible level supplied in the supplying step for only the lowest-frequency sub band is greater than the allowable noise level calculated for the band in the allowable noise level calculating step; substituting, in each one of the bands in which determining step determines that the minimum audible level is greater than the allowable noise level, the minimum audible level supplied in the supplying step for the allowable noise level calculated in the allowable noise level calculating step as the allowable noise level for the one of the bands, and substituting, in each one of the sub bands in the band when the determining step determines that the minimum audible level for the lowest-frequency sub band is greater than the allowable noise level for the band, the minimum audible level supplied for the one of the sub bands in the supplying step for the allowable noise level calculated for the band in the allowable noise level calculating step as the allowable noise level for the one of the sub bands; and adaptively allocating a number of quantizing bits among the bands and the sub bands for quantizing the spectral coefficients therein, the quantizing bits being adaptively allocated to each of the bands and the sub bands in response to the allowable noise level for each of the bands and sub bands. - View Dependent Claims (64, 65, 66, 67, 68)
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Specification