Hybrid Audio Volume Control for Fidelity and Instant Gain Response
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Solution Overview
Problem
Conventional digital audio systems face issues with audio signal fidelity at lower volumes due to loss of resolution in digital volume control and inaccurate instantaneous volume reduction in analog volume control, particularly noticeable in 'soft' audio passages and leading to heat generation in portable systems.
Innovation Solution
A volume control circuit and method that combines analog and digital controls, using a digital gain control circuit to monitor and adjust the output of a variable power supply, ensuring instantaneous volume control without losing signal fidelity and minimizing power consumption, applicable to various modulation techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If digital volume control is used to reduce output volume, then power consumption is reduced, but audio signal fidelity is lost due to resolution loss in digital multiplication
Solution Approach 1:
Instead of applying digital attenuation to reduce volume (which causes resolution loss), the patent inverts the approach by applying digital gain to the complement of the audio signal. This allows the system to achieve volume reduction while maintaining full digital resolution and audio fidelity, as the gain operation preserves all original signal bits.
Solution Approach 2:
The patent changes the operational parameter from digital attenuation (multiplication by a factor less than 1) to digital gain (multiplication by a factor greater than 1) applied to the complement signal. This parameter change enables volume control without the resolution loss inherent in traditional digital attenuation methods.
2Loss of information
If analog volume control is used to reduce output voltage, then audio signal fidelity is maintained, but instantaneous volume reduction is inaccurate due to bulk storage capacitance
Solution Approach 1:
The patent introduces a digital intermediary (the digital gain stage) that compensates for the analog capacitance effect. By detecting when the power supply voltage has not yet responded to a volume change command and applying appropriate digital gain to the complement signal, the system achieves instantaneous and accurate volume control without the lag caused by bulk storage capacitance.
3Speed
If shunt load is used to reduce power supply voltage quickly, then instantaneous volume control is improved, but heat generation increases
Solution Approach 1:
The patent converts the potentially harmful effect of needing rapid voltage reduction into a beneficial digital signal processing operation. Instead of using a shunt load that dissipates power as heat, the system uses digital gain on the complement signal to achieve immediate volume reduction, transforming the problem of slow analog response into an advantage of fast digital processing without thermal byproducts.
Data Source
AI summary
A digital audio system including a combination of analog and digital volume control is disclosed. A variable power supply voltage biases a power amplifier for each channel, and applies a bias voltage corresponding to an analog volume control signal. In one disclosed embodiment, digital gain control circuitry compares the bias voltage with the level expected for the analog volume control signal; if the bias voltage has not dropped in response to a reduction in the analog volume control signal, the digital gain control circuitry reduces the digital gain of the input digital audio signal, until the bias voltage responds to the reduced volume. In another disclosed embodiment, modeling or characterization of the audio system is used to derive a digital gain control signal based on the desired volume signal and the amplitude of the digital audio signal itself. In another disclosed embodiment, a slew rate limiter slows the rate of change of the control signal applied to the variable power supply, in which case the slowed control signal is used in the comparison or calculations of the reduced digital gain.