Audio Decoder Zero-Input Response for CELP–MDCT Transitions
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Solution Overview
Problem
Existing audio decoders face challenges in achieving smooth transitions between CELP and MDCT coding schemes, leading to issues like aliasing and discontinuities due to differences in coding domains, which existing solutions often introduce delays or require significant additional bitrates.
Innovation Solution
An audio decoder that utilizes a transition processor to obtain 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 frame, thereby avoiding delays and maintaining computational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a transition from CELP to MDCT coding scheme is implemented, then coding quality and bitrate efficiency are improved, but discontinuities and aliasing artifacts are introduced at the mode switch boundary
Solution Approach 1:
The patent applies preliminary action by computing the zero-input response of the CELP synthesis filter in advance, before the actual mode transition occurs. This pre-computed response is then used to modify the MDCT decoded signal at the transition boundary, ensuring smooth continuity without requiring complex real-time adjustments during the switch from CELP to MDCT coding mode.
Solution Approach 2:
The patent introduces an intermediary approach by using the zero-input response as a bridge between the CELP and MDCT coding domains. This intermediary signal component is generated from the CELP side and applied to the MDCT side, mediating the transition and eliminating discontinuities that would otherwise occur at the mode switch boundary.
2Reliability
If existing transition solutions are used to avoid discontinuities, then transition smoothness is improved, but processing delay is introduced
Solution Approach 1:
The patent eliminates processing delay by performing the zero-input response computation in advance, before the mode transition point. This pre-computation allows the transition smoothing to be applied immediately at the boundary without requiring additional processing time during or after the actual signal decoding, thus avoiding the delays inherent in conventional transition methods.
3Reliability
If existing transition solutions are used to eliminate aliasing, then transition smoothness is improved, but additional bitrate is required
Solution Approach 1:
The patent applies self-service by utilizing the existing CELP decoded signal and its filter coefficients to generate the zero-input response. This approach leverages resources already available in the CELP decoding process, eliminating the need for additional bitrate allocation. The transition smoothing is achieved by processing existing signal components rather than requiring new data transmission.
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.