EP0446031A2
Expired / Lapsed
EP
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Apparatus for encoding digital signals
Assignee: Sony Corp
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Filing: 1991-03-06
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Granted: —
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Expires: 2011-03-06
Abstract
Abstract Apparatus for efficiently encoding a digital signal includes an arrangement (41, 42) for dividing the signal into a number of frequency band signals. The frequency band signals are segmented into blocks and the blocks are orthogonally transformed (43, 44, 45) to form coefficient data. The coefficient data is then quantized (58). A circuit (50) detects whether at least the lowest frequency one of the frequency band signals contains a transient. If so, a control circuit (57; 102; 100) controls processing of at least the lowest frequency band signal so as to reduce the perceptibility of noise in the processed signal. The control circuit may be operative, in the event of detection of a transient, to increase the number of bits used for quantizing at least the lowest frequency band signal, to reduce the block size of at least the lowest frequency band signal, and/or to reduce the level of at least the lowest frequency band signal.
Inventors
- 👤 Kenzo C/O Patents Division Akagiri
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 00:15
CPC Classifications
H; H03; H03K; H03K21/00; H03K21/40; H04; H04B; H04B1/00; H04B1/66; H04B1/665
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
170 words
Apparatus for encoding a digital signal, the apparatus comprising: frequency dividing means (41, 42) for dividing said digital signal into a plurality of frequency band signals; block segmentation means (43, 44, 45) for segmenting each of said frequency band signals into blocks comprising plural samples of said digital signal; orthogonal transformation means (43, 44, 45) for orthogonally transforming said blocks to form coefficient data; quantization means (58) for quantizing said coefficient data; transient detection means (50) connected to receive at least the lowest frequency one of said frequency band signals, said transient detection means being operative to detect a transient in said signal received thereby and to produce an output indicative of a transient having been detected; and control means (57; 102; 100) responsive to said output produced by the transient detection means (50) indicating that a transient has been detected to control processing of at least said lowest frequency band signal by said apparatus in such a manner as to reduce the perceptibility of noise in the processed signal.
Claim 2
Dependent Claim
80 words
Apparatus according to claim 1, wherein said control means comprises quantizing bit number control means (57) for controlling the number of bits used by the quantization means (58) for quantizing said coefficient data, the quantizing bit number control means (57) being operative to increase the number of bits used for quantizing at least said coefficient data formed from said lowest frequency band signal when said output produced by the transient detection means (50) indicates that a transient has been detected.
Claim 3
Dependent Claim
173 words
Apparatus according to claim 2, wherein said control means (57) comprises: a first memory (57b) storing data, calculated by the quantization means (58) in accordance with a spectral examination of said coefficient data, representative of the number of bits to be used by said quantization means (58); a second memory (57a) storing data that differs from said data stored in said first memory (57b) by an amount appropriate to bring about said increase in the number of bits to be used for quantizing at least said coefficient data formed from said lowest frequency band signal when said output produced by the transient detection means (50) indicates that a transient has been detected; and a switch (57c) normally operative to connect said first memory (57b) to a quantization circuit (24) of the quantization means (58), said switch (57c) being responsive to said output produced by the transient detection means (50) indicating that a transient has been detected to connect said second memory (57a), instead of said first memory (57b), to the quantization circuit (24).
Claim 4
Dependent Claim
128 words
Apparatus according to claim 2, wherein said control means comprises: a memory (72) storing different data, calculated by the quantization means (58) in accordance with a spectral examination of said coefficient data, representative of the number of bits to be used by the quantization means (58) for respective different degrees of transient change; and an address generator (71) capable of generating addresses for said different data, the address generator being connected to receive said output of the transient detection means (50) and being responsive thereto to generate addresses such as to cause the memory (72) to output, for use by a quantization circuit (24) of the quantization means (58), bit number data appropriate to a degree of transient change indicated by said output of the transient detection means.
Claim 5
Dependent Claim
94 words
Apparatus according to any one of the preceding claims, wherein said control means comprises block size control means (102) which forms part of the block segmentation means (43, 44, 45) and is operative to control the size of the blocks (number of samples per block) into which at least said lowest frequency band signal is segmented, the block size control means (102) being operative to decrease the block size of at least said lowest frequency band signal when said output produced by the transient detection means (50) indicates that a transient has been detected.
Claim 6
Dependent Claim
68 words
Apparatus according to any one of the preceding claims, wherein said control means comprises signal level control means (100) for controlling the level of at least said lowest frequency band signal, the signal level control means (100) being operative to decrease the level of at least said lowest frequency band signal when said output produced by the transient detection means (50) indicates that a transient has been detected.
Claim 7
Dependent Claim
112 words
Apparatus according to any one of the preceding claims, wherein the transient detection means (50) comprises: block forming means (46) for segmenting a plurality of samples of said lowest frequency band signal, which plurality is destined to be formed into a said block by the block segmentation means (43, 44, 45), into a plural number of smaller blocks; energy calculating means (47, 48, 49) for calculating the amount of energy in each of said smaller blocks and producing output signals representative thereof; and processing means (51, 52; 51 to 56) operative to form said output of the transient detection means from said output signals of the energy calculating means (47, 48, 49).
Claim 8
Dependent Claim
37 words
Apparatus according to claim 7, wherein said processing means comprises a plurality of dividers (51, 52) operative to divide respective pairs of said output signals of the energy calculating means (47, 48, 49) to produce divided outputs.
Claim 9
Dependent Claim
26 words
Apparatus according to claim 8, including a synthesizing circuit (70; 101) for combining said divided outputs to form said output of the transient detection means (50).
Claim 10
Dependent Claim
114 words
Apparatus according to claim 8, wherein said processing means further comprises: a plurality of comparators (53, 54) each connected to receive a respective one of said divided outputs and each operative to compare said divided output that it receives with a reference input and to generate a predetermined output if said divided output that it receives is equal to a predetermined multiple of said reference input; a logical addition gate (55) connected to receive said predetermined outputs of the comparators (53, 54); and a latch (56) connected to receive an output of said logical addition gate (55) and operative to produce a binary output which forms said output of the transient detection means (50).
Claim 11
Dependent Claim
41 words
Apparatus according to any one of the preceding claims, wherein the frequency dividing means (41, 42) is so operative that the highest frequency one of said frequency band signals has a greater bandwidth than the others of said frequency band signals.
Claim 12
Dependent Claim
48 words
Apparatus according to claim 11, wherein the frequency dividing means (41, 42) is operative to divide a said audio digital signal into three frequency band signals representing substantially 0 to 6 kHz, 6 to 12 kHz, and 12 to 24 kHz bands, respectively, of said audio digital signal.
Claim 13
Dependent Claim
63 words
Apparatus according to any one of the preceding claims, wherein the frequency dividing means comprises a plurality of quadrature mirror filters (41, 42) connected in cascade and each operative to divide an input digital signal applied thereto into a pair of output digital signals each having the frequency information content of a respective half of the frequency range of the input digital signal.
Claim 14
Dependent Claim
49 words
Apparatus according to any one of the preceding claims, wherein the block segmentation means and the orthogonal transformation means are both constituted by a plurality of orthogonal transformation circuits (43, 44, 45), there being a respective one of said orthogonal transformation circuits for each of said frequency band signals.
Claim 15
Dependent Claim
32 words
Apparatus according to any one of the preceding claims, wherein the orthogonal transformation means (43, 44, 45) is operative to orthogonally transform said blocks by subjecting the blocks to fast Fourier transformations.
References Cited (Backward Citations)
No citation records indexed.
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