Wideband Audio Encoding with Selective High-Band Gain Interpolation
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Solution Overview
Problem
Conventional methods for coding wideband signals struggle to maintain similarity between the high frequency band spectrum of an original signal and a newly generated spectrum while achieving a low bit rate, often resulting in discontinuities and degraded sound quality.
Innovation Solution
A coding apparatus that divides the wideband signal into a low frequency band and a high frequency band, codes the low frequency band spectrum, shapes the high frequency band spectrum, and selectively codes the gain of specific locations within the high frequency band, allowing for improved similarity and reduced bit rate through efficient quantization and interpolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If the high frequency band spectrum is replaced with a duplicate of the low frequency band spectrum and uniform gain adjustment is applied, then the bit rate is reduced, but discontinuities occur at the juncture between low and high frequency bands causing degraded sound quality
Solution Approach 1:
The patent applies different gain values to different subbands within the high frequency band instead of using a uniform gain. Specifically, it divides the high frequency band into multiple subbands and calculates separate gain values for each subband based on the spectral characteristics. This local differentiation maintains continuity at band junctures while achieving bit rate reduction through selective quantization.
Solution Approach 2:
The patent segments the high frequency band into multiple subbands and performs independent gain calculation and quantization for each subband. This segmentation allows for more precise control of spectral characteristics and avoids the discontinuities that occur with uniform gain adjustment across the entire high frequency band.
2Measurement precision
If the entire high frequency band spectrum is multiplied uniformly by the same gain, then the energy matches the original signal, but continuity is not maintained between low and high frequency bands
Solution Approach 1:
The patent calculates and applies different gain values to different subbands within the high frequency band. Each subband's gain is determined based on its specific spectral characteristics and its relationship with adjacent bands, ensuring both energy matching and continuity. This local differentiation prevents the discontinuities that occur with uniform gain adjustment.
Solution Approach 2:
The patent dynamically adjusts gains on a subband-by-subband basis rather than applying a static uniform gain across the entire high frequency band. This dynamic approach allows the system to adapt to local spectral variations and maintain continuity while achieving accurate energy matching.
3Reliability
If gain is adjusted on a subband-by-subband basis, then continuity is improved, but the bit rate increases due to the need to code more gain parameters
Solution Approach 1:
The patent applies partial action by performing full gain quantization only for specific subbands (e.g., boundary subbands or subbands with significant spectral characteristics) while using interpolation or duplication for other subbands. This selective approach maintains spectrum continuity where it matters most while reducing the total number of gain parameters that need to be coded, thereby controlling bit rate.
Solution Approach 2:
The patent segments the high frequency band into multiple subbands and applies different coding strategies to different segments. By identifying and prioritizing critical subbands for explicit coding while using interpolation for less critical subbands, the system achieves a balance between continuity and bit rate efficiency.
Data Source
AI summary
There is disclosed an encoding device capable of improving similarity between the high frequency band spectrum of the original signal and a new spectrum to be generated while realizing a low bit rate when encoding a wide-band signal spectrum. The encoding device has sub-band amplitude calculation units (122, 128) for calculating the amplitude of the respective sub-bands for the high frequency band spectrum obtained from the wide-band signal. A search unit (124) and a gain codebook (125) select some sub-bands from a plurality of sub-bands and only the gain of the selected sub-bands is subjected to encoding. An interpolation unit (126) expresses the gain of the sub-band not selected, by mutually interpolating the selected gains.