Audio Decoder Downmix Modification for Artifact Reduction
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Solution Overview
Problem
Audio object coding systems, such as MPEG SAOC, face challenges when downmix signals are manipulated post-processing, leading to mismatches between the transmitted side information and received downmix signals, resulting in artifacts in virtual object reconstructions and sub-optimal output quality.
Innovation Solution
An apparatus and method for decoding encoded audio signals that modifies the transmitted downmix signals to match the original encoder downmix signals using downmix modification functions and gain factors, and applies inverse output signal modification to restore the original mastering effects, ensuring closer alignment with the encoder-created downmix signals and reducing artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If downmix signals are manipulated post-processing to improve audio quality or adapt to different playback scenarios, then audio quality and adaptability are improved, but mismatches occur between transmitted side information and received downmix signals, resulting in artifacts in virtual object reconstructions
Solution Approach 1:
The patent applies inversion by reversing the downmix manipulation operation. Instead of accepting the manipulated downmix signal as-is, the system inverts the manipulation to recover the original encoder downmix signal, thereby eliminating artifacts caused by the mismatch between side information and downmix signal.
Solution Approach 2:
The system uses feedback by transmitting information about the downmix manipulation operation from the decoder back to the encoder side processing. This allows the encoder to be aware of the manipulation and adjust its processing accordingly, or allows the decoder to compensate for the manipulation effects.
2Reliability
If downmix manipulation operations are applied to alter the downmix signal, then beneficial mastering effects are lost, but retaining the original downmix signal causes mismatches with transmitted side information
Solution Approach 1:
The patent segments the processing into two distinct parts: first, the downmix manipulation is applied to preserve beneficial mastering effects; second, the inversion operation is applied specifically to the processed signal to recover the original encoder downmix signal for accurate object reconstruction. This segmentation allows both goals to be achieved separately.
Solution Approach 2:
The system introduces an intermediary processing step that handles the transition between the manipulated downmix signal and the original encoder downmix signal. This intermediary involves computing the inversion operation based on transmitted manipulation information, serving as a bridge between the two signal states.
3Manufacturing precision
If inversion of downmix manipulation is applied to recover original encoder downmix signal, then artifacts are reduced, but additional computational processing is required
Solution Approach 1:
The system applies partial action by selectively inverting only the specific downmix manipulation operations that cause mismatches with side information, rather than reprocessing the entire audio signal chain. This targeted approach reduces computational overhead while maintaining accuracy.
Solution Approach 2:
The inversion operation changes parameters of the downmix signal processing by applying inverse transformation matrices or operations. This parameter-based approach is computationally more efficient than signal-level processing, as it operates in the parameter domain rather than requiring full signal reconstruction and re-processing.
Data Source
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AI summary
An apparatus for decoding an encoded audio signal (100) to obtain modified output signals (160), comprises an input interface (110) for receiving a transmitted downmix signal (112) and parametric data (114) relating to audio objects included in the transmitted downmix signal (112), the downmix signal being different from an encoder downmix signal, to which the parametric data is related; a downmix modifier (116) for modifying the transmitted downmix signal using a downmix modification function, wherein the downmix modification is performed in such a way that a modified downmix signal is identical to the encoder downmix signal or is more similar to the encoder downmix signal compared to the transmitted downmix signal (112); an object renderer (118) for rendering the audio objects using the modified downmix signal and the parametric data to obtain output signals; and an output signal modifier (120) for modifying the output signals using an output signal modification function, wherein the output signal modification function is such that a manipulation operation applied to the encoded downmix signal to obtain the transmitted downmix signal (112) is at least partly applied to the output signals to obtain the modified output signals (160).