Audio Gain Control for Dynamic Range Without Noise Floor Rise
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Solution Overview
Problem
Dynamic range enhancement techniques in audio devices often result in an overestimation of analogue gain, leading to a raised noise floor and reduced performance, particularly when the input signal is close to full scale, due to rounding errors in gain selection.
Innovation Solution
An apparatus and method that limit the analogue gain to the smaller of the calculated gain or the path gain, ensuring the analogue gain never exceeds the path gain, and dynamically adjust digital gains to maintain an optimal noise floor by using limiter circuitry and control circuitry to determine and apply gains based on volume parameters and input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ideal gain is always rounded up to the next quantized value to avoid clipping, then clipping is prevented, but the noise floor is raised when the input signal is close to full scale
Solution Approach 1:
The patent applies dynamic gain selection where the rounding direction (up or down) depends on the current signal level. When the input signal is close to full scale, the system rounds down to prevent noise floor elevation, while for lower signal levels it rounds up to prevent clipping. This dynamic adaptation resolves the contradiction by making the gain quantization strategy signal-dependent rather than fixed.
Solution Approach 2:
The system changes the gain parameter selection based on the input signal amplitude. By monitoring the signal level and adjusting the rounding behavior accordingly, the system optimizes both clipping prevention and noise floor management. The gain value is selected from quantized levels but the selection criterion changes dynamically based on signal conditions.
2Reliability
If high gain is applied to the power amplifier to increase dynamic range, then the dynamic range is increased, but signal noise increases and masks lower-intensity audio signals
Solution Approach 1:
The system performs preliminary digital gain adjustment before the signal reaches the power amplifier. By applying the necessary gain in the digital domain where it does not introduce additional noise, the system prepares the signal for optimal amplification. This preliminary action ensures that the power amplifier operates at its optimal gain level without having to compensate for low signal levels, thus avoiding noise amplification.
Solution Approach 2:
The patent replaces the mechanical/analog gain adjustment in the power amplifier with digital gain adjustment performed by the control circuitry. Digital gain application does not introduce the same noise floor elevation as analog amplifier gain adjustment. By substituting the analog gain mechanism with digital processing, the system achieves dynamic range enhancement without the associated noise penalties.
Data Source
AI summary
An apparatus for providing an output signal to an audio transducer comprises: one or more signal paths for receiving respective digital audio input signals, applying respective digital gains, and outputting respective amplified digital audio input signals; one or more inputs for receiving one or more volume parameters associated with the digital audio input signals; converter circuitry, coupled to the one or more signal paths, for converting the one or more amplified digital audio input signals into the analogue domain, and outputting an analogue audio input signal; an analogue gain element, for applying an analogue gain to the analogue audio input signal and outputting the output signal; and a control circuit, coupled to the one or more signal paths, operative to select the analogue gain based on a comparison of the volume parameters and the one or more digital audio input signals as multiplied by the volume parameters, and to select the respective digital gains for each digital audio input signal so that an overall gain in the respective signal path corresponds to a volume parameter associated with the respective digital audio input signal.