Noise Shaper Gain Ramping to Prevent Audio Pop on Mute
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Solution Overview
Problem
Existing digital audio playback circuits experience an unpleasant transient audio phenomenon known as 'pop' when noise shaping abruptly ceases, leading to inband noise, which is not deterministic in terms of timing.
Innovation Solution
A digital audio playback circuit that includes a noise shaping circuit, a digital-to-analog converter, a muting circuit, and an analog gain control ramp circuit to gradually ramp down the gain when muting, ensuring a predetermined turn-off time for noise shaping to minimize pop occurrence, using a comparator and switches to control current sources and sinks for smooth transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If noise shaping is abruptly ceased when muting, then the turn-off time is reduced, but pop noise and inband noise increase
Solution Approach 1:
The patent applies preliminary action by ramping down the gain of the noise shaper gradually before completely disabling it. The gain control circuit reduces the gain to a predetermined low level over a predetermined time period before turning off the noise shaper, ensuring that the rounding error amplitude is minimized in advance, thus preventing pop noise while maintaining deterministic turn-off timing.
2Object-generated harmful factors
If noise shaping is gradually ramped down, then pop noise is reduced, but the turn-off time becomes non-deterministic
Solution Approach 1:
The patent applies dynamics by implementing a two-stage gain control process. First, the gain is ramped down gradually over a predetermined time period to minimize pop noise. Second, after the gain reaches a predetermined low level, the noise shaper is completely disabled in a deterministic manner. This dynamic approach ensures both pop noise reduction and deterministic turn-off timing.
3Device complexity
If digital turn-off of noise shaper is used, then the circuit complexity is reduced, but the pop noise cannot be controlled
Solution Approach 1:
The patent introduces an intermediary gain control circuit between the digital audio signal and the noise shaper output. This gain control circuit gradually reduces the gain before the noise shaper is turned off, serving as a mediator that prevents abrupt changes in the rounding error amplitude. This intermediary approach effectively controls pop noise while maintaining reasonable circuit complexity.
Data Source
AI summary
A digital audio playback circuit includes a noise shaping circuit configured to receive an input digital audio signal, and a digital to analog converter (DAC) configured to convert the input digital audio signal to a pre-amplified output analog audio signal according to a gain ramp defined by a gain control signal. A muting circuit is configured to compare input digital audio signal to a threshold and assert a mute control signal when the input digital audio signal is below the threshold. An analog gain control ramp circuit is configured to generate the gain control signal in response to the mute control signal to cause the gain ramp to ramp down. An amplifier is configured to amplify the pre-amplified output analog audio signal for playback by an audio playback device.