Digital signal encoding method and apparatus and recording medium
First Claim
1. A method for compressing digital signals comprising the steps of:
- dividing an input signal into at least two bands;
obtaining frequency-domain data of said at least two bands of the input signal; and
acting on at least one characteristic of said frequency domain data;
wherein said step of acting on at least one characteristic acts on frequency-domain characteristics and includes;
a multiplication coefficient calculating sub-step of calculating the size of frequency-domain spectral data, allocating the frequency characteristic operating information on said spectral data for normalization and outputting coefficients for multiplication;
an overflow check sub-step of checking whether or not a result of multiplication of said spectral data with the multiplication coefficient supplied from said multiplication coefficient calculating sub-step exceeds a pre-set upper limit;
a coefficient correcting step of normalizing the coefficients from said multiplication coefficient calculating sub-step in their entirety if, judging from an output of said overflow check sub-step, there are a large number of frequency domain spectral data for which occurs the overflow;
a storage step of correcting the coefficients so that an output of said coefficient correction sub-step will exhibit moderate changes;
an aliasing noise reducing sub-step of correcting an output of said coefficient correcting sub-step to characteristics maintaining symmetry with respect to a cut-off frequency as an axis of symmetry for canceling previous aliasing noise; and
a multiplication sub-step of multiplying the coefficients corrected by said aliasing noise reducing sub-step with the frequency-domain spectral data.
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Abstract
A digital signal compressing device includes a unit for dividing an input signal into plural bands duping information compression, a unit for producing frequency-domain data of the input signal divided into plural bands, and a unit for operating on frequency-domain characteristics. The unit for operating on frequency-domain characteristics operates on the frequency-domain characteristics so that the condition of canceling the aliasing noise by the frequency division and subsequent frequency synthesis performed by a synthesis filter in association with the division at the time of information expansion will be maintained. The frequency-domain characteristics of the input signal can be acted on easily without obstructing the condition of canceling the aliasing noise without requiring a new mechanism or device other than the information compressing mechanism or device.
63 Citations
22 Claims
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1. A method for compressing digital signals comprising the steps of:
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dividing an input signal into at least two bands; obtaining frequency-domain data of said at least two bands of the input signal; and acting on at least one characteristic of said frequency domain data; wherein said step of acting on at least one characteristic acts on frequency-domain characteristics and includes; a multiplication coefficient calculating sub-step of calculating the size of frequency-domain spectral data, allocating the frequency characteristic operating information on said spectral data for normalization and outputting coefficients for multiplication; an overflow check sub-step of checking whether or not a result of multiplication of said spectral data with the multiplication coefficient supplied from said multiplication coefficient calculating sub-step exceeds a pre-set upper limit; a coefficient correcting step of normalizing the coefficients from said multiplication coefficient calculating sub-step in their entirety if, judging from an output of said overflow check sub-step, there are a large number of frequency domain spectral data for which occurs the overflow; a storage step of correcting the coefficients so that an output of said coefficient correction sub-step will exhibit moderate changes; an aliasing noise reducing sub-step of correcting an output of said coefficient correcting sub-step to characteristics maintaining symmetry with respect to a cut-off frequency as an axis of symmetry for canceling previous aliasing noise; and a multiplication sub-step of multiplying the coefficients corrected by said aliasing noise reducing sub-step with the frequency-domain spectral data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for compressing digital signals comprising the steps of:
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dividing an input signal into at least two bands; obtaining frequency-domain data of said at least two bands of the input signal; and acting on at least one characteristic of said frequency domain data; wherein said step of acting on at least one characteristic acts on frequency-domain characteristics for maintaining the condition of canceling aliasing noise that results from the frequency division; wherein said step of acting on at least one characteristic includes; a multiplication coefficient calculating sub-step of calculating the size of frequency-domain spectral data, allocating the frequency characteristic operating information on said spectral data for normalization and outputting coefficients for multiplication; an overflow check sub-step of checking whether or not a result of multiplication of said spectral data with the multiplication coefficient supplied from said multiplication coefficient calculating sub-step exceeds a pre-set upper limit; a coefficient correcting step of normalizing the coefficients from said multiplication coefficient calculating sub-step in their entirety if, judging from an output of said overflow check sub-step, there are a large number of frequency domain spectral data for which occurs the overflow; a storage step of correcting the coefficients so that an output of said coefficient correction sub-step will exhibit moderate changes; an aliasing noise reducing sub-step of correcting an output of said coefficient correcting sub-step to characteristics maintaining symmetry with respect to a cut-off frequency fs/4 as an axis of symmetry for canceling previous aliasing noise; and a multiplication sub-step of multiplying the coefficients corrected by said aliasing noise reducing sub-step with the frequency-domain spectral data and wherein said step of dividing an input signal into at least two bands uses a QMF filter made up at least of a low-pass filter and a high-pass filter and said step of acting on at least one characteristic affords such characteristics that the equation ##EQU13## is satisfied, an impulse response of the high-pass filter will meet the equation;
##EQU14## and impulse responses g1, g2 of synthesis filters G1, G2 will meet the equation;
##EQU15## where f1 (n) is an impulse response of the low-pass filter and F1(n) its z-transform. - View Dependent Claims (10, 11, 12)
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13. A device for compressing digital signals comprising:
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means for dividing an input signal into at least two bands;
means for obtaining frequency-domain data of said at least two bands of the input signal; andmeans for acting on at least one characteristic of said frequency-domain data;
wherein said means for acting on at least one characteristic acts on frequency-domain characteristics for maintaining the condition of canceling the aliasing noise that results from the frequency divisionwherein said means for acting on at least one characteristic includes; a multiplication coefficient calculating circuit for calculating the size of frequency-domain spectral data, allocating the frequency characteristic operating information on said spectral data for normalization and outputting coefficients for multiplication; an overflow check circuit for checking whether or not a result of multiplication of said spectral data with the multiplication coefficient supplied from said multiplication coefficient calculating means exceeds a pre-set upper limit; a coefficient correcting circuit for normalizing the coefficients from said multiplication coefficient calculating means in their entirety if, judging from an output of said overflow check sub-step, there are a large number of frequency domain spectral data for which occurs the overflow; a memory for correcting the coefficients so that an output of said coefficient correction means will exhibit moderate changes;
an aliasing noise reducing circuit for correcting an output of said coefficient correcting means to characteristics maintaining symmetry with respect to a cut-off frequency as an axis of symmetry for canceling previous aliasing noise; anda multiplier for multiplying the coefficients corrected by said aliasing noise reducing means with the frequency-domain spectral data. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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20. A device for compressing digital signals comprising:
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means for dividing an input signal into at least two bands;
means for obtaining frequency-domain data of said at least two bands of the input signal; andmeans for acting on at least one characteristic of said frequency-domain data;
wherein said means for acting on at least one characteristic acts on frequency-domain characteristics for maintaining the condition of canceling aliasing noise by the frequency division,wherein said means for dividing an input signal into at least two bands uses a QMF filter made up at least of a low-pass filter and a high-pass filter and said means for acting on at least one characteristic affords such characteristics that the equation ##EQU19## is satisfied, an impulse response of the high-pass filter will meet the equation;
##EQU20## and impulse responses g1, g2 of synthesis filters G1, G2 will meet the equation;
##EQU21## where f1(n) is an impulse response of the low-pass filter and F1(n) its z-transform; andwherein said means for acting on at least one characteristic includes; a multiplication coefficient calculating circuit for calculating the size of frequency-domain spectral data, allocating the frequency characteristic operating information on said spectral data for normalization and outputting coefficients for multiplication; an overflow check circuit for checking whether or not a result of multiplication of said spectral data with the multiplication coefficient supplied from said multiplication coefficient calculating means exceeds a pre-set upper limit; a coefficient correcting circuit for normalizing the coefficients from said multiplication coefficient calculating means in their entirety if, judging from an output of said overflow check sub-step, there are a large number of frequency domain spectral data for which occurs the overflow; a memory for correcting the coefficients so that an output of said coefficient correction means will exhibit moderate changes;
an aliasing noise reducing circuit for correcting an output of said coefficient correcting means to characteristics maintaining symmetry with respect to a cut-off frequency as an axis of symmetry for canceling previous aliasing noise; anda multiplier for multiplying the coefficients corrected by said aliasing noise reducing means with the frequency-domain spectral data. - View Dependent Claims (21, 22)
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Specification