Alternating Predictive and Transform Audio Encoding
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Solution Overview
Problem
Existing coding techniques for alternating speech and music signals, such as AMR-WB+ and USAC RM0, suffer from insufficient music quality due to suboptimal transform coding and window energy concentration, and incur algorithmic delays incompatible with conversational applications.
Innovation Solution
A method that alternates between predictive and transform coding by reusing parameters from the preceding frame for restricted predictive coding of a part of the current frame, allowing for aliasing term recovery and reduced bit rate impact, with a transition frame that maintains a consistent weighting window size for transform coding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transform coding is used for music signals, then coding quality is improved, but algorithmic delay increases
Solution Approach 1:
The current frame is divided into two parts: a first part coded by restricted predictive coding and a second part coded by transform coding. This segmentation allows the system to apply transform coding only where necessary while maintaining lower delay for time-critical portions of the signal.
Solution Approach 2:
Different coding techniques are applied to different parts of the same frame based on local signal characteristics. The first part uses predictive coding suitable for speech-like segments, while the second part uses transform coding for music-like segments, optimizing quality where needed without incurring delay everywhere.
2Quantity of substance
If parameter reuse in restricted predictive coding is implemented, then bit rate is reduced, but coding flexibility decreases
Solution Approach 1:
Instead of reusing all predictive coding parameters, only selected parameters are reused in the restricted predictive coding of the first part. This partial action reduces bit rate while maintaining sufficient coding flexibility for speech-like segments where parameters change slowly.
Solution Approach 2:
The system selectively changes parameters between frames based on signal type. For speech-like segments, parameters are reused to reduce bit rate; for music-like segments, full parameter updates are performed to maintain flexibility and quality.
3Measurement precision
If alternating predictive and transform coding is used, then overall coding quality is improved, but system complexity increases
Solution Approach 1:
The frame is segmented into two parts with different coding methods, allowing the system to manage complexity by processing only portions of the signal with computationally intensive transform coding while using simpler predictive coding for other portions.
Solution Approach 2:
The system applies different coding complexities to different parts of the signal based on local requirements. Speech-like segments receive simpler predictive coding while music-like segments receive more complex transform coding, optimizing the balance between quality and computational complexity.
Data Source
AI summary
An encoder and a method for encoding a digital signal are provided. The method includes encoding a preceding frame of samples of the digital signal according to a predictive encoding process, and encoding a current frame of samples of the digital signal according to a transform encoding process. The method is implemented such that a first portion of the current frame is also encoded by predictive encoding that is limited relative to the predictive encoding of the preceding frame by reusing at least one parameter of the predictive encoding of the preceding frame and only encoding the parameters of said first portion of the current frame that are not reused. A decoder and a decoding method are also provided, which correspond to the described encoding method.