Audio Decoder Zero-Input Response for Smooth CELP–MDCT Transitions
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Solution Overview
Problem
Existing switched audio codecs face challenges in achieving smooth transitions between CELP and MDCT coding schemes, leading to aliasing and discontinuities due to differences in coding domains, with existing solutions often introducing delays or requiring significant additional side-information.
Innovation Solution
An audio decoder utilizing a transition processor that obtains a zero-input response of a linear predictive filter, adjusting the initial state based on both decoded audio information frames to modify the second decoded audio information for a seamless transition, without altering the first decoded audio information, thereby avoiding delays and computational overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a transition from CELP codec to MDCT-based codec is implemented in switched audio coding, then coding quality and bitrate efficiency are improved, but discontinuities and aliasing artifacts are introduced at the border between frames
Solution Approach 1:
The patent applies preliminary action by computing the zero-input-response of the linear predictive filter in advance, based on the first decoded audio frame, before the actual mode switching occurs. This pre-computed response is then used to modify the second decoded audio frame, ensuring smooth transition without discontinuities when switching from CELP to MDCT coding mode.
Solution Approach 2:
The patent introduces an intermediary mechanism by using the zero-input-response as a bridge between the two different coding domains. This intermediary signal, derived from the CELP frame, is combined with the MDCT frame to eliminate discontinuities at the mode switching boundary, effectively mediating between the two different encoding schemes.
2Object-generated harmful factors
If existing solutions address CELP-to-MDCT transition problems, then aliasing and discontinuities are reduced, but processing delay is introduced
Solution Approach 1:
The patent eliminates processing delay by performing the zero-input-response computation in advance, before mode switching occurs. The response is pre-computed based on the first decoded frame and stored, so that when the second frame is decoded, the transition can be applied immediately without introducing additional delay to the audio stream.
3Object-generated harmful factors
If existing solutions address CELP-to-MDCT transition problems, then transition smoothness is improved, but additional side-information is required
Solution Approach 1:
The patent applies self-service by utilizing the already-decoded first audio frame and its associated linear predictive filter parameters to generate the zero-input-response. This eliminates the need for separate side-information transmission, as the system uses its own existing resources (the first frame and its filter coefficients) to create the transition smoothing signal.
Data Source
AI summary
An audio decoder is disclosed. In one example, the audio decoder is for providing a decoded audio information on the basis of an encoded audio information includes a linear-prediction-domain decoder configured to provide a first decoded audio information on the basis of an audio frame encoded in a linear prediction domain, a frequency domain decoder configured to provide a second decoded audio information on the basis of an audio frame encoded in a frequency domain, and a transition processor. The transition processor is configured to obtain a zero-input-response of a linear predictive filtering, wherein an initial state of the linear predictive filtering is defined depending on the first decoded audio information and the second decoded audio information, and modify the second decoded audio information depending on the zero-input-response, to obtain a smooth transition between the first and the modified second decoded audio information.