EP0525809A2
Expired / Lapsed
EP
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Digital encoder with dynamic quantization bit allocation
Assignee: Sony Corp
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Filing: 1992-07-31
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Granted: —
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Expires: 2012-07-31
Abstract
Abstract A digital encoder for compressing a digital input signal derived from an analog signal to reduce the number of bits required to represent the analog signal with low quantizing noise. In the encoder, a digital input signal representing the analog signal is divided into three frequency ranges. The digital signal in each of the three frequency ranges is divided in time into frames, the time duration of which may be adaptively varied. The frames are orthogonally transformed into spectral coefficients, which are grouped into critical bands. The total number of bits available for quantizing the spectral coefficients is allocated among the critical bands. In a first embodiment and a second embodiment, fixed bits are allocated among the critical bands according to a selected one of a plurality of predetermined bit allocation patterns and variable bits are allocated among the critical bands according to the energy in the critical bands. In the first embodiment, the apportionment between fixed bits and variable bits is fixed. In a second embodiment, the apportionment between fixed bits and variable bits is varied according to the smoothness of the spectrum of the input signal. In a third embodiment, bits are allocated among the critical bands according to a noise shaping factor that is varied according to the smoothness of the spectrum of the input signal. All three embodiments give low quantizing noise with both broad spectrum signals and highly tonal signals.
Inventors
- 👤 Kenzo Akagiri
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-26 08:35
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/66; H04B1/665
Claims Analysis
Total Claims: 60
Claim 1
Independent Claim
187 words
A digital encoding apparatus for compressing a digital input signal to provide a compressed output signal, the apparatus comprising: first frequency dividing means for receiving the digital input signal and for dividing the digital input signal into a plurality of frequency ranges; time dividing means for dividing in time at least one of the frequency ranges of the digital input signal into a plurality of frames; second frequency dividing means for orthogonally transforming each frame to provide a plurality of spectral coefficients; means for grouping the plurality of spectral coefficients into critical bands; bit allocating means for allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands, and means for allocating the variable bits in response to signal energy in a data block derived by dividing the digital input signal in time and in frequency.
Claim 2
Dependent Claim
187 words
A digital encoding apparatus for compressing a digital input signal to provide a compressed output signal, the apparatus comprising: first frequency dividing means for receiving the digital input signal and for dividing the digital input signal into a plurality of frequency ranges; time dividing means for dividing in time at least one of the frequency ranges of the digital input signal into a plurality of frames; second frequency dividing means for orthogonally transforming each frame to provide a plurality of spectral coefficients; means for grouping the plurality of spectral coefficients into critical bands; bit allocating means for allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands, and means for allocating the variable bits in response to signal energy in a data block derived by dividing the digital input signal in time and in frequency.
Claim 3
Dependent Claim
23 words
The digital encoding apparatus of claim 1, wherein the number of fixed bits is constant and the number of variable bits is constant.
Claim 4
Dependent Claim
55 words
The digital encoding apparatus of claim 2, additionally comprising bit pattern selecting means for selecting one of a plurality of predetermined bit patterns, the bit pattern selecting means selecting a predetermined bit pattern having fewer bits allocated to high-frequency critical bands than to middle frequency critical bands when the digital input signal has low energy.
Claim 5
Dependent Claim
29 words
The digital encoding apparatus of claim 3, wherein the bit pattern selecting means selects one of the plurality of predetermined bit patterns in response to the digital input signal.
Claim 6
Dependent Claim
30 words
The digital encoding apparatus of claim 3, wherein the bit pattern selecting means selects one of the plurality of predetermined bit patterns in response to energy in a critical band.
Claim 7
Dependent Claim
47 words
The digital encoding apparatus of claim 3, wherein the bit pattern selecting means selects one of the plurality of predetermined bit patterns in response to a signal derived by further dividing in frequency but not in time one of the frequency ranges of the digital input signal.
Claim 8
Dependent Claim
37 words
The digital encoding apparatus of claim 2, wherein each frame has a duration in time, and the time dividing means is additionally for adaptively changing duration in time of the frames in each of the frequency ranges.
Claim 9
Dependent Claim
8 words
The digital encoding apparatus of claim 1, wherein
Claim 10
Dependent Claim
29 words
each frame has a duration in time, and the time dividing means is additionally for adaptively changing duration in time of the frames in each of the frequency ranges.
Claim 11
Dependent Claim
29 words
each frame has a duration in time, and the time dividing means is additionally for adaptively changing duration in time of the frames in each of the frequency ranges.
Claim 12
Dependent Claim
35 words
The digital encoding apparatus of claim 1, wherein the bit allocation means includes a means for apportioning the total number of quantizing bits available for quantizing the spectral coefficients between fixed bits and variable bits.
Claim 13
Dependent Claim
55 words
The digital encoding apparatus of claim 9, additionally comprising bit pattern selecting means for selecting one of a plurality of predetermined bit patterns, the bit pattern selecting means selecting a predetermined bit pattern having fewer bits allocated to high-frequency critical bands than to middle frequency critical bands when the digital input signal has low energy.
Claim 14
Dependent Claim
29 words
The digital encoding apparatus of claim 10, wherein the bit pattern selecting means selects one of the plurality of predetermined bit patterns in response to the digital input signal.
Claim 15
Dependent Claim
30 words
The digital encoding apparatus of claim 10, wherein the bit pattern selecting means selects one of the plurality of predetermined bit patterns in response to energy in a critical band.
Claim 16
Dependent Claim
47 words
The digital encoding apparatus of claim 10, wherein the bit pattern selecting means selects one of the plurality of predetermined bit patterns in response to a signal derived by further dividing in frequency, but not in time, one of the frequency ranges of the digital input signal.
Claim 17
Dependent Claim
100 words
The digital encoding apparatus of claim 9, wherein the digital input signal has a spectrum having a smoothness, the apparatus includes a spectral smoothness index generating means for generating a spectral smoothness index in response to the smoothness of the spectrum of the digital input signal, and the means for apportioning the total number of quantizing bits available for quantizing the spectral coefficients between fixed bits and variable bits increases the number of quantizing bits allocated to fixed bits and decreases the number of quantizing bits allocated to variable bits in response to an increase in the spectral smoothness index.
Claim 18
Dependent Claim
29 words
The apparatus of claim 14, wherein the spectral smoothness index generating means derives the spectral smoothness index in response to a measured difference in energy between adjacent critical bands.
Claim 19
Dependent Claim
57 words
The apparatus of claim 14, wherein the apparatus additionally comprises a floating point processing means for floating point processing the spectral components and for generating floating point data for each critical band, and the spectral smoothness index generating means derives the spectral smoothness index in response to a difference in floating point data between adjacent critical bands.
Claim 20
Dependent Claim
37 words
The digital encoding apparatus of claim 9, wherein each frame has a duration in time, and the time dividing means is additionally for adaptively changing duration in time of the frames in each of the frequency ranges.
Claim 21
Dependent Claim
181 words
A digital encoding apparatus for compressing a digital input signal to provide a compressed digital output signal, the digital input signal representing an audio information signal, the compressed digital output signal, after expansion, conversion to an analog signal, and reproduction of the analog signal, being for perception by the human ear, the apparatus comprising: first frequency dividing means for receiving the digital input signal and for dividing the digital input signal into a plurality of frequency ranges; time dividing means for dividing in time at least one of the frequency ranges of the digital input signal into a plurality of frames; second frequency dividing means for orthogonally transforming each frame to provide a plurality of spectral coefficients; means for grouping the plurality of spectral coefficients into critical bands; noise factor setting means for setting a noise shaping factor in response to the digital input signal; and bit allocating means for allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor.
Claim 22
Dependent Claim
181 words
A digital encoding apparatus for compressing a digital input signal to provide a compressed digital output signal, the digital input signal representing an audio information signal, the compressed digital output signal, after expansion, conversion to an analog signal, and reproduction of the analog signal, being for perception by the human ear, the apparatus comprising: first frequency dividing means for receiving the digital input signal and for dividing the digital input signal into a plurality of frequency ranges; time dividing means for dividing in time at least one of the frequency ranges of the digital input signal into a plurality of frames; second frequency dividing means for orthogonally transforming each frame to provide a plurality of spectral coefficients; means for grouping the plurality of spectral coefficients into critical bands; noise factor setting means for setting a noise shaping factor in response to the digital input signal; and bit allocating means for allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor.
Claim 23
Dependent Claim
36 words
The digital encoding apparatus of claim 18, wherein the digital input signal has an amplitude, and the noise factor setting means sets the noise shaping factor in response to the amplitude of the digital input signal.
Claim 24
Dependent Claim
80 words
The digital encoding apparatus of claim 19, wherein the compressed output signal, after expansion, conversion to an analog signal and reproduction of the analog signal, has quantizing noise, the quantizing noise having a spectrum, the quantizing noise being dependent on the allocation of the quantizing bits among the critical bands, and the noise factor setting means sets the noise shaping factor such that, as the amplitude of the digital input signal increases, the spectrum of the quantizing noise is flattened.
Claim 25
Dependent Claim
42 words
The digital encoding apparatus of claim 18, wherein the digital input signal has a spectrum having a smoothness, and the noise factor setting means sets the noise shaping factor in response to the smoothness of the spectrum of the digital input signal.
Claim 26
Dependent Claim
83 words
The digital encoding apparatus of claim 21, wherein the compressed output signal, after expansion, conversion to an analog signal and reproduction of the analog signal, has quantizing noise, the quantizing noise having a spectrum, the quantizing noise being dependent on the allocation of the quantizing bits among the critical bands, and the noise factor setting means sets the noise shaping factor such that, as the smoothness of the spectrum of the digital input signal increases, the spectrum of the quantizing noise is flattened.
Claim 27
Dependent Claim
61 words
The digital encoding apparatus of claim 22, wherein the apparatus additionally includes a spectral smoothness index generating means for generating a spectral smoothness index in response to the smoothness of the spectrum of the digital input signal, and the spectral smoothness index generating means derives the spectral smoothness index in response to a measured difference in energy between adjacent critical bands.
Claim 28
Dependent Claim
88 words
The digital encoding apparatus of claim 22, wherein the apparatus additionally includes a spectral smoothness index generating means for generating a spectral smoothness index in response to the smoothness of the spectrum of the digital input signal, the apparatus additionally comprises a floating point processing means for floating point processing the spectral components and for generating floating point data for each critical band, and the spectral smoothness index generating means derives the spectral smoothness index in response to a difference in floating point data between adjacent critical bands.
Claim 29
Dependent Claim
47 words
The apparatus of claim 21, wherein the digital input signal additionally has an amplitude, and the bit allocation means changes the allocation of quantization bits in response to a signal having diminished spectral levels at high frequencies when the amplitude of the digital input signal is small.
Claim 30
Dependent Claim
40 words
The apparatus of claim 25, wherein the digital input signal has a minimum audibility frequency, and the high frequency spectral levels are diminished for digital input signal amplitudes that are small at frequencies not lower than the minimum audibility frequency.
Claim 31
Independent Claim
274 words
An apparatus for decoding a compressed digital input signal to provide a digital output signal, the compressed digital input signal being derived from a non-compressed digital input signal by the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands, generating quantizing word length data indicating the number of bits used to quantize the spectral coefficients in each critical band; and multiplexing the quantized spectral coefficients and the word length data to provide the compressed digital input signal; the decoder comprising: demultiplexing means for extracting the quantizing word-length data from the compressed digital input signal and for extracting the spectral coefficients from the compressed digital input signal using the quantizing word-length data, means for grouping the extracted spectral coefficients into a plurality of frequency ranges; means for performing an inverse orthogonal transform on the spectral coefficients in each frequency range to generate frames of time-dependent data in each frequency range; and means for combining the frames of time-dependent data in each frequency range to provide the digital output signal.
Claim 32
Independent Claim
274 words
An apparatus for decoding a compressed digital input signal to provide a digital output signal, the compressed digital input signal being derived from a non-compressed digital input signal by the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands, generating quantizing word length data indicating the number of bits used to quantize the spectral coefficients in each critical band; and multiplexing the quantized spectral coefficients and the word length data to provide the compressed digital input signal; the decoder comprising: demultiplexing means for extracting the quantizing word-length data from the compressed digital input signal and for extracting the spectral coefficients from the compressed digital input signal using the quantizing word-length data, means for grouping the extracted spectral coefficients into a plurality of frequency ranges; means for performing an inverse orthogonal transform on the spectral coefficients in each frequency range to generate frames of time-dependent data in each frequency range; and means for combining the frames of time-dependent data in each frequency range to provide the digital output signal.
Claim 33
Independent Claim
304 words
An apparatus for decoding a compressed digital input signal to provide a digital output signal, the compressed digital input signal being derived from a non-compressed digital input signal, the non-compressed digital input signal representing an audio information signal, the compressed digital input signal, after decoding, conversion to an analog signal, and reproduction of the analog signal, being for perception by the human ear, the compressed digital input signal being derived from the non-compressed digital input signal by the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; setting a noise shaping factor in response to the non-compressed digital input signal; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor; generating quantizing word length data indicating the number of bits used to quantize the spectral coefficients in each critical band; and multiplexing the quantized spectral coefficients and the word length data to provide the compressed digital input signal; the decoder comprising: demultiplexing means for extracting the quantizing word-length data from the compressed digital input signal and for extracting the spectral coefficients from the compressed digital input signal using the quantizing word-length data, means for grouping the extracted spectral coefficients into a plurality of frequency ranges; means for performing an inverse orthogonal transform on the spectral coefficients in each frequency range to generate frames of time-dependent data in each frequency range; and means for combining the frames of time-dependent data in each frequency range to provide the digital output signal.
Claim 34
Independent Claim
304 words
An apparatus for decoding a compressed digital input signal to provide a digital output signal, the compressed digital input signal being derived from a non-compressed digital input signal, the non-compressed digital input signal representing an audio information signal, the compressed digital input signal, after decoding, conversion to an analog signal, and reproduction of the analog signal, being for perception by the human ear, the compressed digital input signal being derived from the non-compressed digital input signal by the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; setting a noise shaping factor in response to the non-compressed digital input signal; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor; generating quantizing word length data indicating the number of bits used to quantize the spectral coefficients in each critical band; and multiplexing the quantized spectral coefficients and the word length data to provide the compressed digital input signal; the decoder comprising: demultiplexing means for extracting the quantizing word-length data from the compressed digital input signal and for extracting the spectral coefficients from the compressed digital input signal using the quantizing word-length data, means for grouping the extracted spectral coefficients into a plurality of frequency ranges; means for performing an inverse orthogonal transform on the spectral coefficients in each frequency range to generate frames of time-dependent data in each frequency range; and means for combining the frames of time-dependent data in each frequency range to provide the digital output signal.
Claim 35
Independent Claim
151 words
A medium for recording compressed digital data derived from a non-compressed digital input signal by a process including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 36
Independent Claim
151 words
A medium for recording compressed digital data derived from a non-compressed digital input signal by a process including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 37
Dependent Claim
12 words
The medium of claim 29, wherein the medium is an optical disc.
Claim 38
Dependent Claim
12 words
The medium of claim 29, wherein the medium includes a semiconductor memory.
Claim 39
Dependent Claim
21 words
The medium of claim 29, wherein the number of fixed bits is constant and the number of variable bits is constant.
Claim 40
Dependent Claim
43 words
The medium of claim 32, wherein, in the process, each frame has a duration in time, and the step of dividing each frequency range by time includes the step of adaptively changing the duration in time of the frames in each frequency range.
Claim 41
Dependent Claim
32 words
The medium of claim 29, wherein the process includes the additional step of allocating the total number of quantizing bits available for quantizing the spectral coefficients between fixed bits and variable bits.
Claim 42
Dependent Claim
103 words
The medium of claim 34, wherein, in the process, the non-compressed digital input signal has a spectrum having a smoothness, the process includes the additional step of generating a spectral smoothness index in response to the smoothness of the spectrum of the non-compressed digital input signal, and in the step of allocating the total number of quantizing bits available for quantizing the spectral coefficients between fixed bits and variable bits, the number of quantizing bits allocated to fixed bits is increased and the number of quantizing bits allocated to variable bits is decreased in response to an increase in the spectral smoothness index.
Claim 43
Dependent Claim
43 words
The medium of claim 34, wherein, in the process, each frame has a duration in time, and the step of dividing each frequency range by time includes the step of adaptively changing the duration in time of the frames in each frequency range.
Claim 44
Independent Claim
133 words
A medium for recording compressed digital data derived from a non-compressed digital input signal by a process including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; setting a noise shaping factor in response to the non-compressed digital input signal; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 45
Independent Claim
133 words
A medium for recording compressed digital data derived from a non-compressed digital input signal by a process including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; setting a noise shaping factor in response to the non-compressed digital input signal; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 46
Dependent Claim
42 words
The medium of claim 37, wherein, in the process, the non-compressed digital input signal has an amplitude, and the step of setting a noise factor includes setting the noise shaping factor in response to the amplitude of the non-compressed digital input signal.
Claim 47
Dependent Claim
48 words
The medium of claim 37, wherein, in the process: the non-compressed digital input signal has a spectrum having a smoothness, and the step of setting a noise factor includes setting the noise shaping factor in response to the smoothness of the spectrum of the non-compressed digital input signal.
Claim 48
Independent Claim
150 words
A method for deriving compressed digital data from a non-compressed digital input signal, the method including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; and allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 49
Independent Claim
150 words
A method for deriving compressed digital data from a non-compressed digital input signal, the method including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; and allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the total number of bits including: fixed bits to be allocated among the critical bands according to a selected one of a plurality predetermined bit allocation patterns, and variable bits to be allocated among the critical bands according to signal energy in the critical bands; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 50
Dependent Claim
21 words
The method of claim 40, wherein the number of fixed bits is constant and the number of variable bits is constant.
Claim 51
Dependent Claim
40 words
The method of claim 41, wherein: each frame has a duration in time, and the step of dividing each frequency range by time includes the step of adaptively changing the duration in time of the frames in each frequency range.
Claim 52
Dependent Claim
8 words
The method of claim 40, wherein the method
Claim 53
Dependent Claim
24 words
includes the additional step of allocating the total number of quantizing bits available for quantizing the spectral coefficients between fixed bits and variable bits.
Claim 54
Dependent Claim
24 words
includes the additional step of allocating the total number of quantizing bits available for quantizing the spectral coefficients between fixed bits and variable bits.
Claim 55
Dependent Claim
100 words
The method of claim 43, wherein: the non-compressed digital input signal has a spectrum having a smoothness, the method includes the additional step of generating a spectral smoothness index in response to the smoothness of the spectrum of the non-compressed digital input signal, and in the step of allocating the total number of quantizing bits available for quantizing the spectral coefficients between fixed bits and variable bits, the number of quantizing bits allocated to fixed bits is increased and the number of quantizing bits allocated to variable bits is decreased in response to an increase in the spectral smoothness index.
Claim 56
Dependent Claim
40 words
The method of claim 43, wherein: each frame has a duration in time, and the step of dividing each frequency range by time includes the step of adaptively changing the duration in time of the frames in each frequency range.
Claim 57
Independent Claim
131 words
A method for deriving compressed digital data from a non-compressed digital input signal, the method including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; setting a noise shaping factor in response to the non-compressed digital input signal; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 58
Independent Claim
131 words
A method for deriving compressed digital data from a non-compressed digital input signal, the method including the steps of: dividing the non-compressed digital input signal into a plurality of frequency ranges; dividing in time each of the frequency ranges of the non-compressed digital input signal into a plurality of frames; orthogonally transforming each frame to provide a plurality of spectral coefficients; grouping the plurality of spectral coefficients into critical bands; setting a noise shaping factor in response to the non-compressed digital input signal; allocating among the critical bands a total number of quantizing bits available for quantizing the spectral coefficients, the quantizing bits being allocated among the critical bands according to the noise-shaping factor; and multiplexing the quantized spectral coefficients and quantizing word length data to provide the compressed digital data.
Claim 59
Dependent Claim
39 words
The method of claim 46, wherein: the non-compressed digital input signal has an amplitude, and the step of setting a noise factor includes setting the noise shaping factor in response to the amplitude of the non-compressed digital input signal.
Claim 60
Dependent Claim
45 words
The method of claim 46, wherein: the non-compressed digital input signal has a spectrum having a smoothness, and the step of setting a noise factor includes setting the noise shaping factor in response to the smoothness of the spectrum of the non-compressed digital input signal.
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