Microphone Analog Gain Control Using Digital Power Estimation
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Solution Overview
Problem
In telephony, the quality of audio signals transmitted between near-end and far-end is affected by varying gain settings due to changes in speech proximity to the microphone, leading to signal saturation or low signal-to-noise ratio, which degrades performance in modules like automatic speech recognition, echo cancellation, and noise cancellation.
Innovation Solution
A gain control system comprising a power estimator, digital gain estimator, and gain controller that adjusts analogue gain based on estimated signal power and voice detection to maintain a target power level, with variable adjustment rates and echo cancellation capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high gain is applied to the microphone signal, then the signal-to-noise ratio is improved, but signal saturation occurs leading to poor audio quality
Solution Approach 1:
The patent implements dynamic gain control by continuously monitoring the power level of the microphone signal and adjusting the gain accordingly. When the signal power exceeds a threshold, the gain is reduced to prevent saturation; when the signal power is low, the gain is increased to improve signal-to-noise ratio. This dynamic adaptation resolves the contradiction between needing high gain for noise reduction and avoiding saturation.
Solution Approach 2:
The system employs feedback mechanisms where the output signal power is monitored and fed back to control the gain adjustment. The power estimator continuously measures the signal power, and this information is used to adjust the gain in real-time, creating a closed-loop control system that prevents saturation while maintaining adequate signal levels.
2Object-affected harmful factors
If low gain is applied to the microphone signal, then signal saturation is avoided, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The gain control system dynamically adjusts the gain level based on real-time signal power measurements. When the input signal power is low, the system increases the gain to boost the signal level and improve signal-to-noise ratio. When the signal power is high, the gain is reduced to prevent saturation. This dynamic behavior resolves the contradiction between avoiding saturation and maintaining signal quality.
Solution Approach 2:
The system changes the gain parameter adaptively based on the signal power level. By monitoring the power of the microphone signal and adjusting the gain parameter in response to power variations, the system maintains optimal signal-to-noise ratio while preventing saturation across varying speech conditions.
3Object-affected harmful factors
If the gain is adjusted in real-time to follow speech power changes, then audio quality is maintained, but the performance of signal processing modules such as echo cancellation and noise cancellation deteriorates
Solution Approach 1:
The system performs preliminary gain adjustment before the signal enters other processing modules. By pre-adjusting the gain to an optimal level based on signal power estimation, the signal is normalized in a way that actually improves the performance of subsequent modules like echo cancellation and noise cancellation, rather than degrading it. The gain control prepares the signal in advance for optimal processing.
Solution Approach 2:
The patent implements dynamic gain control that adapts to speech conditions while maintaining compatibility with other signal processing modules. The gain adjustment is performed in a coordinated manner that considers the requirements of downstream processing modules, ensuring that echo cancellation, noise cancellation, and other modules maintain their effectiveness while audio quality is optimized.
Data Source
AI summary
A gain control system for controlling gain applied to an audio signal includes a power estimator configured to estimate the power of a digital signal derived from the audio signal, a digital gain estimator configured to determine, in dependence on the estimated power, a digital gain which would modify the power of the digital signal so as to reach a target power level, and a gain controller configured to adjust an analogue gain applied to the audio signal in dependence on the determined digital gain.