Audio Gain Adjustment for Noisy High-Band Speech Coding
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Solution Overview
Problem
In super wideband telephony, the correlation between the low-band and high-band signals can be weak in noisy conditions, leading to inaccurate signal modeling and artifacts such as distorted speech due to inadequate encoding of the high-band signal.
Innovation Solution
Noise modulation and gain adjustment techniques are employed to improve signal reconstruction by adaptively smoothing the mixing ratio of low-band excitation to modulated noise for high-band synthesis and determining gain parameters to compensate for quantization distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-band signal is not fully encoded and transmitted to improve coding efficiency, then bandwidth usage is reduced, but signal reconstruction accuracy deteriorates due to weak correlation between low-band and high-band in noisy conditions
Solution Approach 1:
The patent performs preliminary noise detection and characterization on the low-band signal before high-band synthesis. By pre-calculating noise parameters and adjusting the mixing factor accordingly, the system prepares the excitation signal in advance to better represent the actual high-band signal characteristics under noisy conditions, improving reconstruction accuracy without full encoding
Solution Approach 2:
The patent dynamically adjusts the mixing factor between transformed low-band excitation signal and modulated noise based on real-time noise conditions. The mixing factor is adapted frame-by-frame or sub-frame-by-sub-frame according to the detected correlation strength between low-band and high-band, allowing the system to optimize the balance between coding efficiency and reconstruction accuracy under varying noise levels
2Loss of substance
If transformed low-band excitation signal is used for high-band synthesis to reduce data transmission, then transmission bandwidth is reduced, but audible artifacts increase due to inadequate representation of high-band signal in noisy conditions
Solution Approach 1:
The patent introduces modulated noise as an intermediary component in the high-band excitation signal. This modulated noise, shaped by the adjusted mixing factor and noise characteristics, acts as a mediator that fills in the gaps where the transformed low-band excitation signal is inadequate, particularly under noisy conditions, thereby reducing audible artifacts while maintaining reduced data transmission
Solution Approach 2:
The patent changes the parameters of the excitation signal by adjusting the mixing factor between the transformed low-band excitation signal and modulated noise. This parameter adjustment allows the system to adapt the composition of the high-band excitation signal based on noise conditions, improving the representation accuracy and reducing artifacts without increasing the transmitted data volume
3Device complexity
If mixing ratio of low-band excitation to modulated noise is not adaptively adjusted in noisy conditions, then system complexity is reduced, but signal reconstruction quality deteriorates due to fluctuations in mixing parameters
Solution Approach 1:
The patent implements a feedback mechanism where the system detects noise characteristics and correlation strength between low-band and high-band signals, then uses this information to adjust the mixing factor accordingly. This closed-loop feedback ensures that the mixing ratio is adaptively optimized based on actual signal conditions, improving reconstruction reliability while maintaining reasonable system complexity through efficient noise estimation algorithms
Data Source
AI summary
A method of performing gain adjustment in an electronic device includes determining a first set of spectral frequency values and determining a second set of spectral frequency values. The first set of spectral frequency values corresponds to a high-band portion of an audio signal received at the electronic device. The second set of spectral frequency values approximates the first set of spectral frequency values in the high band portion of the audio signal. The method includes estimating a spectral distortion corresponding to a difference between the first set of spectral frequency values and the second set of spectral frequency values and adjusting, based on the spectral distortion, a gain value corresponding to at least a portion of the audio signal. The method also includes transmitting an encoded bitstream that includes information corresponding to the adjusted gain value and the second set of spectral frequency values.