Hybrid Audio Codec Block Switching for Transient Signal Coding
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Solution Overview
Problem
The low delay hybrid codec experiences sound quality deterioration due to aliasing when switching between different coding modes, and it lacks an effective method for coding transient signals, particularly with the AAC-ELD mode using a long window shape that impairs transient signal coding.
Innovation Solution
Implementing optimal block switching algorithms for seamless mode transitions between AAC-ELD, ACELP, and TCX modes, and using short windowing for transient signal encoding to improve sound quality by reducing bitrate and enhancing coding performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If AAC-ELD mode with long window shape is used for low delay coding, then algorithm delay is reduced to 20 ms or less, but transient signal coding performance deteriorates
Solution Approach 1:
The patent applies dynamics by making the window shape adaptive rather than fixed. The AAC-ELD mode can switch between long window shape (for low delay) and short window shape (for transient signals) based on the signal characteristics. This dynamic adaptation allows the system to maintain low algorithm delay while improving transient signal coding performance when needed.
Solution Approach 2:
The patent changes the window shape parameter from a fixed long window to a variable parameter that can be adjusted between long and short window shapes. This parameter change enables the system to optimize for transient signal coding by using short window shapes when transient signals are detected, while maintaining low delay operation with long window shapes for other signals.
2Adaptability or versatility
If block switching is performed between different coding modes (AAC-ELD, ACELP, TCX), then adaptability to different signal types is improved, but aliasing occurs causing sound quality deterioration
Solution Approach 1:
The patent applies preliminary action by performing preparation work before the actual mode switching occurs. When a mode transition is detected, the system pre-processes the boundary samples by applying appropriate windowing functions and performing overlap-add operations in advance. This preliminary action ensures that aliasing is prevented at the switching boundaries, maintaining sound quality while enabling adaptability between different coding modes.
Solution Approach 2:
The patent uses an intermediary approach by introducing transition frames that mediate between different coding modes. These transition frames contain specially processed samples that bridge the gap between modes, using overlap-add synthesis with appropriate windowing functions. This intermediary mechanism prevents direct discontinuities and aliasing that would occur with abrupt mode switching.
3Manufacturing precision
If speech codec (ACELP/TCX) is used for audio signal coding, then sound quality for wideband audio is improved, but bitrate requirement increases compared to speech codec
Solution Approach 1:
The patent applies universality by creating a hybrid codec system that can perform multiple functions - it can operate as a speech codec (ACELP/TCX) when speech signals are detected, and as an audio codec (AAC-ELD) when wideband audio signals are detected. This multi-functional approach allows the system to achieve high sound quality for both speech and audio while optimizing bitrate usage by selecting the appropriate coding mode for each signal type.
Data Source
AI summary
A new hybrid audio decoder and a new hybrid audio encoder having block switching for speech signals and audio signals are provided. Currently, very low bitrate audio coding methods for speech and audio signals are proposed. These audio coding methods cause very long delays. Generally, in coding an audio signal, an algorithm delay tends to be long to achieve higher frequency resolution. In coding a speech signal, the delay needs to be reduced because the speech signal is used for telecommunication. To balance fine coding quality for speech and audio input signals with very low bitrate, a combination of a low delay filter bank like AAC-ELD and a CELP coding method is provided.