Selective bass post filter
First Claim
1. A decoder system for decoding a bit stream signal as an audio time signal, the decoder system including:
- a decoding section for decoding the bit stream signal as a preliminary audio time signal, wherein the decoding section comprises a code-excited linear prediction, CELP, decoding module and a transform-coded excitation, TCX, decoding module; and
an interharmonic noise attenuation post filter adapted to receive the preliminary audio time signal, and to supply the audio time signal, wherein the post filter comprises a control section for selectively operating the post filter in one of the following modes;
i) a filtering mode, wherein the post filter filters the preliminary audio time signal to obtain a filtered signal and supplies the filtered signal as the audio time signal; and
ii) a pass-through mode, wherein the post filter supplies the preliminary audio time signal as the audio time signal,wherein the decoder system selectively operates in one of the following modes;
a) the TCX module is enabled and the post filter is operated in the pass-through mode;
b) the CELP module is enabled and, in response to a post-filtering signal, the post filter is operated in the filtering mode; and
c) the CELP module is enabled and, in response to the post-filtering signal, the post filter is operated in the pass-through mode.
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Accused Products
Abstract
In one aspect, the invention provides an audio encoding method characterized by a decision being made as to whether the device which will decode the resulting bit stream should apply post filtering including attenuation of interharmonic noise. Hence, the decision whether to use the post filter, which is encoded in the bit stream, is taken separately from the decision as to the most suitable coding mode. In another aspect, there is provided an audio decoding method with a decoding step followed by a post-filtering step, including interharmonic noise attenuation, and being characterized in a step of disabling the post filter in accordance with post filtering information encoded in the bit stream signal. Such a method is well suited for mixed-origin audio signals by virtue of its capability to deactivate the post filter in dependence of the post filtering information only, hence independently of factors such as the current coding mode.
28 Citations
16 Claims
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1. A decoder system for decoding a bit stream signal as an audio time signal, the decoder system including:
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a decoding section for decoding the bit stream signal as a preliminary audio time signal, wherein the decoding section comprises a code-excited linear prediction, CELP, decoding module and a transform-coded excitation, TCX, decoding module; and an interharmonic noise attenuation post filter adapted to receive the preliminary audio time signal, and to supply the audio time signal, wherein the post filter comprises a control section for selectively operating the post filter in one of the following modes; i) a filtering mode, wherein the post filter filters the preliminary audio time signal to obtain a filtered signal and supplies the filtered signal as the audio time signal; and ii) a pass-through mode, wherein the post filter supplies the preliminary audio time signal as the audio time signal, wherein the decoder system selectively operates in one of the following modes; a) the TCX module is enabled and the post filter is operated in the pass-through mode; b) the CELP module is enabled and, in response to a post-filtering signal, the post filter is operated in the filtering mode; and c) the CELP module is enabled and, in response to the post-filtering signal, the post filter is operated in the pass-through mode. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of decoding a bit stream signal as an audio time signal, comprising:
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decoding the bit stream signal as a preliminary audio time signal in one of a plurality of decoding modes, the plurality of decoding modes comprising code-excited linear prediction, CELP, and transform-coded excitation, TCX, decoding modes; and filtering the preliminary audio time signal with an interharmonic noise attenuation post-filter to obtain the audio time signal, wherein the post-filter comprises a control section for selectively operating the post-filter in one of the following modes; i) a filtering mode, wherein the post filter filters the preliminary audio time signal to obtain a filtered signal and supplies the filtered signal as the audio time signal; and ii) a pass-through mode, wherein the post-filter supplies the preliminary audio time signal as the audio time signal, wherein decoding the bit stream signal as an audio time signal comprises selectively operating in one of the following modes; a) enabling the TCX decoding mode and operating the post-filter in the pass-through mode; b) enabling the CELP decoding mode and, in response to a post-filtering signal, operating the post-filter in the filtering mode; and c) enabling the CELP decoding mode and, in response to the post-filtering signal, operating the post-filter in the pass-through mode. - View Dependent Claims (8)
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9. An encoder system for encoding an audio time signal as a bit stream signal, including an encoding section operable in several coding modes, for encoding an audio time signal as a bit stream signal,
the encoder system comprising a decision section adapted to decide whether post filtering, which includes attenuation of interharmonic noise, is to be disabled at decoding of the bit stream signal separately from deciding on the coding mode and to encode this decision in the bit stream signal as post filtering information, the decision section being adapted to: -
detect a co-presence of a signal component with dominant fundamental frequency and a signal component located below the fundamental frequency and, optionally, between its harmonics; and responsive to a positive determination, to take a decision to disable. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A method of encoding an audio time signal as a bit stream signal, the method including the steps of:
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encoding an audio time signal as a bit stream signal in one of several coding modes, and deciding whether post filtering, which includes attenuation of interharmonic noise, is to be disabled at decoding of the bit stream signal separately from deciding on the coding mode and encoding this decision in the bit stream signal as post filtering information, wherein deciding whether post filtering is to be disabled comprises; detecting a co-presence of a signal component with dominant fundamental frequency and a signal component located below the fundamental frequency and, optionally, between its harmonics; and responsive to a positive determination, deciding to disable post-filtering. - View Dependent Claims (16)
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Specification