Patent US4900501A successfully refreshed from Google Patents.
EP0143584A2
Expired / Lapsed
EP
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Sub-band coders, decoders and filters
Assignee: British Telecommunications PLC
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Filing: 1984-11-15
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Granted: —
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Expires: 2004-11-15
Abstract
Abstract A pair of filters (H 1 H 2 ) split an input signal into two fre- dency sub-bands (defined by a transition frequency) which de down-sampled and coded: after sample rate restoration the gnals are filtered (K 1 K 2 ) and combined. To reduce signal elays, the delay response of each filter is non-constant, aving a maximum at or beyond the transition frequency. referably non-quadrature filter pairs are used. Filters may e cascaded for more than two sub-bands.
Inventors
- 👤 Paul Christopher Millar
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 07:25
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/66; H04B1/667; G; G10; G10L; G10L19/00; G10L19/02; G10L19/0204
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
60 words
1 A filter arrangement comprising a pair of first and second filters for passing respectively frequencies above and below a transition frequency, in which the amplitude responses and the delay responses of the filters are mirror images about the transition frequency, the filters are not quadrature filters and the delay response with respect to frequency of each filter is non-constant.
Claim 2
Dependent Claim
60 words
1 A filter arrangement comprising a pair of first and second filters for passing respectively frequencies above and below a transition frequency, in which the amplitude responses and the delay responses of the filters are mirror images about the transition frequency, the filters are not quadrature filters and the delay response with respect to frequency of each filter is non-constant.
Claim 3
Dependent Claim
17 words
2 A filter arrangement according to claim 1 in which the filters are minimum phase response filters.
Claim 4
Dependent Claim
30 words
3 A filter arrangement according to claim 1 or 2, in which the delay responses of the first and second filters have maxima respectively above and below the transition frequency.
Claim 5
Dependent Claim
18 words
4 A filter arrangement according to any one of the preceding claims in which the filters are recursive.
Claim 6
Dependent Claim
35 words
5 A filter arrangement according to any one of claims 1 to 4 for splitting an input signal into two or more frequency sub-bands, the first and second filters being supplied from a common input.
Claim 7
Dependent Claim
45 words
6 A filter arrangement for splitting an input signal into four or more frequency sub-bands, comprising a first pair of filters according to claim 5, the outputs of the first and second filters thereof being connected to the inputs of respective further such filter pairs.
Claim 8
Dependent Claim
32 words
7 A filter arrangement according to any one of claims 1 to 4 in which the two filters have separate inputs, and including means for combining the outputs of the two filters.
Claim 9
Dependent Claim
41 words
8 A filter arrangement for combining four or more frequency sub-bands into a single output, comprising at least one pair of filter arrangements according to claim 7, the outputs of which are connected to the inputs of a further such arrangement.
Claim 10
Dependent Claim
34 words
9 A sub-band coding apparatus having an input for a sampled input signal, a filter arrangement according to claim 5 or 6 for filtering the sampled signal, and means for down-sampling the filtered outputs.
Claim 11
Dependent Claim
35 words
10 A decoding apparatus comprising means for restoring the sample rate of down-sampled sub-band input signals, and a filter arrangement according to claim 7 or 8 for combining the signals to produce a decoded output.
Claim 12
Dependent Claim
104 words
11 A transmission system comprising: a coder having an input for a sampled signal, a filter arrangement according to claim 6 for filtering the sampled signal, and means for down-sampling the filter outputs; and a decoder comprising means for restoring the sample rate of the down-sampled signals, and a filter arrangement according to claim 8 for combining the signals to produce a decoded output; in which the filter parameters are selected such that the overall delay response of the system is, over a substantial portion of the system bandwidth, substantially equi-ripple and the spacing of the peaks of the delay response is substantially uniform.
Claim 13
Dependent Claim
25 words
12 A transmission system according to claim 11 in which the decoder includes a polyphase all-pass filter for equalising the delay response of the system.
References Cited (Backward Citations)
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