ΔΣ Modulator Feedback Coefficient Control for Audio Noise Suppression
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Solution Overview
Problem
Conventional ΔΣ modulators generate noise and degrade the signal-to-noise ratio (S/N ratio) when no audio signal is input or when the signal input state alternates with a no-signal state, particularly due to the circulation of data as feedback in accumulators.
Innovation Solution
An audio output device with a ΔΣ modulator that includes a multiplier coefficient control circuit to reduce the multiplier coefficient to 0 stepwise when no digital audio signal is input, thereby eliminating residual data in the accumulator and preventing noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If accumulators are used in the ΔΣ modulator to improve sound quality, then the sound quality is improved, but noise is generated when no audio signal is input which worsens the S/N ratio
Solution Approach 1:
The feedback coefficient is made dynamic rather than fixed. When an audio signal is detected, the feedback coefficient is set to 1 for normal operation. When no audio signal is detected, the feedback coefficient is changed to 0 to prevent noise circulation. This dynamic adjustment resolves the contradiction by adapting the system behavior to the presence or absence of input signals.
Solution Approach 2:
The invention changes the parameter of the feedback coefficient in the accumulator based on the detection of audio signal presence. By transitioning the feedback coefficient from 1 to 0 when no signal is detected, the system eliminates the harmful noise circulation while maintaining the beneficial accumulation function during normal operation, thus resolving the S/N ratio degradation issue.
2Measurement precision
If higher-order ΔΣ modulators with multiple cascaded accumulators are used to improve sound quality, then the sound quality is improved, but the influence of noise is increased when no signal is input
Solution Approach 1:
Each accumulator in the cascaded structure employs dynamic feedback coefficient control. When no audio signal is detected, all feedback coefficients are simultaneously changed to 0, preventing noise circulation through any of the accumulators. This maintains the advantages of higher-order modulation while eliminating the compounding noise issue.
Solution Approach 2:
The invention introduces a feedback mechanism that monitors the presence of audio signals and adjusts the feedback coefficients accordingly. The feedback coefficient control section receives detection results and modifies the feedback paths in real-time, enabling the system to switch between normal operation mode and noise-prevention mode, thus resolving the contradiction between sound quality improvement and noise suppression.
3Reliability
If the feedback coefficient is maintained at 1 for normal operation, then the ΔΣ modulator functions correctly during audio signal input, but residual data circulate as feedback signals generating noise when no signal is input
Solution Approach 1:
The feedback coefficient is dynamically adjusted between two states: 1 during audio signal input for reliable modulator operation, and 0 when no audio signal is detected to prevent noise generation from residual data circulation. This dynamic switching resolves the contradiction by adapting the feedback strength to the operational context.
Solution Approach 2:
The invention takes preliminary action by detecting the absence of audio signals before noise can be generated by circulating residual data. When no signal is detected, the feedback coefficient is proactively changed to 0 to prevent the harmful effect of noise circulation, rather than attempting to eliminate noise after it has been generated.
Data Source
AI summary
Provided is an audio output device capable of preventing noises and improving the S/N ratio even if no audio signal is inputted in the middle of the input of audio signals, or even if an audio-signal input state and a no-signal state are alternately repeated. In the provided audio output device, a multiplier is provided on the input side of each of the delayers. Each multiplier multiplies the addition output of the corresponding one of adders by a multiplier coefficient supplied by the coefficient counter. If there is no input of digital audio signals into a ΔΣ modulator, the counter control circuit decreases the output of the coefficient counter down to 0 stepwise at predetermined intervals.