Voice Quality Enhancement via Low Bit-Rate Speech Coding Detection
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Solution Overview
Problem
Low bit-rate speech coders, such as Advanced MultiBand Excitation (AMBE) coding, degrade voice quality by introducing spectral imbalances that result in 'thinness' of lower frequency speech content and excessive high-frequency sibilance, without network signaling to indicate the type of coding used.
Innovation Solution
A method and apparatus that detect the presence of low bit-rate coding in speech signals and apply corrective measures, including bass boost and sibilance filtering, to enhance voice quality by dynamically mixing correction signals based on detected degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If low bit-rate speech coding (e.g., AMBE) is employed to increase channel capacity, then bit rate is reduced, but voice quality deteriorates due to spectral imbalance
Solution Approach 1:
The patent converts the harmful spectral imbalance introduced by low bit-rate coding into a beneficial correction opportunity. By detecting the specific spectral characteristics of AMBE-coded speech (excessive high-frequency content, deficient low-frequency content), the system applies targeted spectral shaping filters that restore natural speech quality. The harmful artifacts become identifiable markers that trigger automatic correction, turning a quality degradation problem into a solvable detection-and-correction workflow.
Solution Approach 2:
The patent dynamically adjusts spectral parameters by applying frequency-dependent gain adjustments. The spectral shaping filter modifies the amplitude spectrum by boosting low-frequency components and attenuating excessive high-frequency components based on detected coding type. This parameter change approach allows the system to adapt the spectral balance in real-time, compensating for the fixed spectral distortion introduced by the low bit-rate coder.
2Object-affected harmful factors
If spectral correction filters are applied to improve voice quality, then voice quality improves, but processing complexity increases
Solution Approach 1:
The patent implements a self-service mechanism where the speech signal itself provides the information needed for correction. The detection algorithm analyzes inherent spectral characteristics of the coded speech to automatically identify when AMBE coding is present and triggers appropriate correction. This self-service approach eliminates the need for external signaling or manual intervention, allowing the system to autonomously detect and correct quality issues without adding significant operational complexity.
Solution Approach 2:
The patent establishes a feedback loop where the output of spectral analysis feeds into the correction mechanism. The system continuously monitors spectral balance, detects deviations caused by low bit-rate coding, and dynamically adjusts filter parameters accordingly. This closed-loop feedback ensures that correction is applied only when and where needed, optimizing processing efficiency while maintaining voice quality.
Data Source
AI summary
To increase channel capacity, mobile phone carriers have deployed speech coders, such as Advanced MultiBand Excitation coding (AMBE), in networks to reduce the bit rate of each call. One undesired consequence of employing such speech coders is that the voice quality can be much worse as compared to higher bit-rate speech coders. A method or corresponding apparatus in an example embodiment of the present invention performs voice quality enhancement transparently within a network by detecting use of a coder applying rate reduction to a speech signal and known to have an adverse effect on a coded speech signal. Upon detection of the use of such coder, the coded speech signal is corrected based on components introduced into the coded speech signal due to the rate reduction. As a result of applying the voice quality enhancement, adverse effects of speech coders can be reduced, while maintaining high quality voice signals.