Stereo Signal Encoding Apparatus for Bitrate Reduction
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Solution Overview
Problem
The challenge is to reduce bit rate in stereo signal transmission without compromising quality, particularly when applying intermittent transmission techniques, as energy steps in spectral sub-bands degrade quality and increasing bit rate is necessary to avoid these steps.
Innovation Solution
A stereo signal encoding and decoding apparatus that encodes and decodes stereo signals by generating and using monaural signal spectral parameters, along with information on the variation between these parameters and channel signals, to efficiently transmit and reconstruct stereo signals during speech and non-speech frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If panning coefficients are used to encode stereo signal in sub-bands, then stereo spatial effect is achieved, but energy steps occur in spectra between sub-bands degrading quality
Solution Approach 1:
The patent segments the stereo signal into multiple frequency sub-bands and applies different encoding strategies to each band. By dividing the spectrum into sub-bands, the system can apply panning coefficients selectively to certain bands while using alternative methods (such as intensity stereo or joint stereo) in other bands where energy steps would degrade quality, thus resolving the contradiction between encoding simplicity and spectral quality.
Solution Approach 2:
The patent applies different encoding quality levels to different frequency regions. In frequency bands where energy steps would significantly degrade perception, the system uses higher-quality encoding methods with fewer panning coefficients or alternative representations. In bands where panning coefficients work well, the system maintains simpler encoding. This local adaptation resolves the contradiction by optimizing quality where it matters most while maintaining overall simplicity.
2Manufacturing precision
If bit rate is increased to avoid energy steps in spectral sub-bands, then quality is improved, but transmission efficiency decreases
Solution Approach 1:
The patent dynamically changes encoding parameters such as the number of sub-bands, the quantization precision of panning coefficients, and the selection of stereo encoding modes based on the characteristics of the input signal. By adapting these parameters to the signal content, the system achieves high quality where necessary while reducing bit rate in less critical regions, thus resolving the contradiction between quality and transmission efficiency.
Solution Approach 2:
The patent applies full-resolution panning coefficients only to the extent necessary to maintain quality, rather than uniformly across all frequency bands. By applying encoding resources partially—focusing on critical bands and reducing precision in non-critical bands—the system achieves acceptable quality at lower overall bit rates, resolving the contradiction between quality and efficiency.
3Manufacturing precision
If sub-bands are narrowed to suppress energy steps, then spectral quality is improved, but number of panning coefficients increases raising bit rate
Solution Approach 1:
The patent uses a moderate number of frequency sub-bands rather than excessive segmentation. By choosing an optimal number of sub-bands that balances spectral smoothness with coefficient count, the system avoids energy steps without generating an excessive number of panning coefficients. This segmentation strategy resolves the contradiction by finding the optimal granularity level for encoding.
Solution Approach 2:
The patent narrows sub-bands only to the extent necessary to suppress perceptible energy steps, rather than using excessively fine segmentation. By applying partial narrowing—just enough to eliminate audible artifacts while maintaining reasonable coefficient counts—the system achieves spectral smoothness without excessively increasing bit rate, resolving the contradiction between quality and data quantity.
Data Source
AI summary
A stereo signal encoding device is provided that enables a lower bitrate without decreasing quality when applying an intermittent transmission technique to a stereo signal. A stereo encoding unit generates first stereo encoded data by encoding the stereo signal when the stereo signal of the current frame is an audio section. A stereo DTX encoding unit is a means for encoding the stereo signal when the stereo signal of the current frame is a non-audio section. The stereo DTX encoding unit generates second stereo encoded data by encoding each of a monaural signal spectral parameter that is a spectral parameter of a monaural signal generated using the first channel signal and the second channel signal, first channel signal information relating to the first channel signal, and second channel signal information relating to the second channel signal.