Audio Decoder Frame Recovery Using LSF Stabilization
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Solution Overview
Problem
Existing audio codecs face challenges in smoothly transitioning between concealed and received frames due to mismatches in Linear Prediction Coefficients (LPC) and excitation, particularly during frame loss, which can lead to noticeable artifacts in speech signals.
Innovation Solution
An audio decoder employs dual sets of LPC parameter decoding units to generate two synthesis signals, allowing for a selection based on energy-related measurements to ensure a seamless transition, using a first set derived from concealed frames and a second set from properly received frames, with optional energy compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single LPC parameter decoding unit is used for frame recovery, then device complexity is reduced, but manufacturing precision of frame transition quality deteriorates due to mismatch between concealed and received frames
Solution Approach 1:
The decoder is segmented into two distinct LPC parameter decoding units: a first decoding unit that processes LPC parameters from properly received frames, and a second decoding unit that processes LPC parameters from concealed frames. This segmentation allows independent optimization of each decoding path, enabling precise control over frame transitions while maintaining manageable device complexity through modular architecture.
2Manufacturing precision
If energy compensation is applied during frame recovery, then manufacturing precision of energy consistency is improved, but use of energy by the decoder increases due to additional computational operations
Solution Approach 1:
Energy compensation is applied partially rather than universally - specifically during frame recovery operations when transitioning from concealed to received frames. The compensation mechanism selectively adjusts energy parameters only when needed to maintain consistency, avoiding unnecessary computational overhead during normal decoding operations where energy consistency is already maintained.
3Manufacturing precision
If dual sets of LPC parameter decoding units are implemented, then manufacturing precision of frame recovery quality is improved through better energy matching, but device complexity increases due to additional decoding components
Solution Approach 1:
The decoder is segmented into two distinct LPC parameter decoding units: a first decoding unit that processes LPC parameters from properly received frames, and a second decoding unit that processes LPC parameters from concealed frames. This segmentation allows independent optimization of each decoding path, enabling precise control over frame transitions while maintaining manageable device complexity through modular architecture.
Solution Approach 2:
An energy compensation mechanism acts as an intermediary between the two decoding units and the synthesis stage. This intermediary component adjusts energy parameters to ensure smooth transitions during frame recovery, mediating the interaction between concealed and received frames while maintaining overall system coherence and reducing the impact of increased complexity.
4Loss of information
If blind recovery is used without transmitted side information, then loss of information is reduced, but measurement precision of recovery accuracy deteriorates due to lack of encoder-decoder synchronization
Solution Approach 1:
The decoder performs self-service during frame recovery by using its own internal concealed frame parameters and energy compensation mechanisms to achieve accurate reconstruction. Rather than relying on externally transmitted side information from the encoder, the system uses its own decoded parameters and applies energy matching to maintain recovery accuracy, enabling blind recovery without sacrificing precision.
Data Source
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AI summary
There is provided an Audio decoder (100) for synthesizing an audio signal from a bitstream which represents the audio signal, the audio decoder (100) including: a bitstream receiver (5), to receive the bitstream representative of the audio signal, the bitstream having, encoded therein, a set of encoded audio parameters (ΔLSFq) for each frame of the audio signal, a first audio parameter decoding unit (10), to decode, for a current properly received frame, a first set of decoded audio parameters (ai1) from at least the set of encoded audio parameters, a concealment unit (40) to conceal at least one non-properly received frame based on at least one previously properly received frame, so as to generate at least one set of concealment audio parameters; a second audio parameter decoding unit (20), to decode, for a current properly received frame which immediately follows the at least one previously non-properly received frame, a second set of decoded audio parameters (ai2) from at least the set of encoded audio parameters, the second set of decoded audio parameters (ai2) being different from the first set of decoded audio parameters (ai1); a synthesizing unit (50), to output, or derive, an output or derived version of the synthesized audio signal in such way that, if the current properly received frame immediately follows the at least one previously non-properly received frame, a selection (60) is made between: a first version (s1) of the synthesized audio signal, synthesized from at least the first set of decoded audio parameters; and a second version (s2) of the synthesized audio signal, synthesized from the second set of decoded audio parameters.