Linear-Prediction Audio Decoder for Smooth Frequency-Domain Switching
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Solution Overview
Problem
Existing audio codecs face challenges in achieving smooth transitions between CELP-based and MDCT-based coding schemes, leading to issues such as 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 modify decoded audio information using a zero-input response of a linear predictive filter, considering both initial states of the first and second decoded audio information, to achieve a smooth transition without additional delay or increased bitrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a CELP-to-MDCT transition is performed in switched audio coding, 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 linear predictive filter in advance, before the actual mode transition occurs. This pre-computed response is then used to modify the MDCT frame at the transition boundary, ensuring smooth continuity without requiring additional delay or increasing bitrate. The zero-input response captures the necessary transition characteristics beforehand, allowing the harmful discontinuity artifacts to be eliminated proactively.
2Reliability
If existing solutions are used to avoid CELP-to-MDCT discontinuities, then audio quality is improved, but decoding delay is introduced
Solution Approach 1:
The patent employs self-service by utilizing the zero-input response of the linear predictive filter, which is inherently available from the CELP decoding process itself. Instead of requiring external correction signals or additional processing stages that would introduce delay, the system leverages the filter's own response characteristics to achieve smooth transitions. The zero-input response is computed using the same filter coefficients and initial states already present in the decoder, making the transition process self-contained and delay-free.
3Reliability
If existing solutions are used to avoid CELP-to-MDCT discontinuities, then audio quality is improved, but additional bitrate is required
Solution Approach 1:
The patent applies the taking out principle by extracting only the essential information needed for smooth transition from the existing CELP decoding process. Specifically, it extracts the zero-input response, which can be computed from the linear predictive filter coefficients and initial states that are already being processed during normal CELP decoding. This extraction avoids the need to transmit additional side information or correction signals, as the necessary transition data is already implicitly available in the decoder's internal state, thereby maintaining bitrate efficiency while improving audio quality.
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.