Audio Distortion Estimation for Adaptive Loudspeaker Control
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Solution Overview
Problem
Audio systems, particularly those in vehicles and mobile devices, suffer from distortion due to non-linearities in loudspeakers and amplifiers, with existing methods either requiring accurate nonlinear models or failing to predict distortion in complex cases, such as when multiple sine waves are applied.
Innovation Solution
An audio system comprising an audio processor, amplifier, loudspeaker, distortion estimator, and controller that estimates the expected non-linear response of the loudspeaker and amplifier, generating a distortion prediction signal to vary operating parameters like gain and compression ratio, and applies perceptual weighting to reduce perceived distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a loudspeaker model is used to pre-distort an input signal to linearise the response, then distortion is reduced for moderate displacements, but the system cannot accurately predict distortion for large displacements
Solution Approach 1:
The system dynamically adapts the audio processing parameters based on the estimated distortion level. The controller adjusts the operating parameters of the audio processor in real-time according to the distortion prediction signal, allowing the system to maintain accuracy across varying displacement conditions rather than relying on a fixed model
Solution Approach 2:
The distortion estimator provides feedback about the expected non-linear response to the controller, which then adjusts the audio processor parameters accordingly. This closed-loop approach allows the system to compensate for distortion dynamically based on actual system behavior rather than relying solely on pre-established models
2Measurement precision
If the input voltage is limited to keep frequency magnitude components below a maximum voltage, then distortion is reduced to acceptable levels, but the system cannot accurately predict distortion in the general case with multiple sine waves
Solution Approach 1:
The distortion estimator acts as an intermediary that predicts distortion levels without requiring complex multi-frequency measurements. By using a simplified estimation approach based on the relationship between input signal characteristics and expected non-linear response, the system avoids the complexity of measuring and storing maximum voltages for multiple frequency combinations while still providing effective distortion control
Solution Approach 2:
The system changes the operating parameters of the audio processor based on the distortion prediction signal. Rather than fixing the input voltage limits based on worst-case scenarios, the system dynamically adjusts parameters like gain and compression ratio according to the predicted distortion level, achieving better overall performance with simpler control
3Measurement precision
If pre-distortion is applied using an accurate nonlinear model, then linear response is achieved, but the system requires very accurate model data and performs heavily dependent on model accuracy
Solution Approach 1:
The system uses simpler, less accurate distortion estimation models that do not require precise non-linear loudspeaker characteristics. Instead of investing in complex, accurate non-linear modeling, the system employs a more robust approach that estimates distortion based on general non-linear behavior patterns, reducing the burden of model accuracy while still achieving effective distortion control through dynamic parameter adjustment
Data Source
AI summary
An audio system is described including an audio processor, an amplifier and a speaker and a distortion estimator. The distortion estimator calculates at least one of an expected response of the amplifier to an audio signal and an expected response of the loudspeaker to an audio signal. The distortion estimator is operable to generate a distortion prediction signal determined by a difference between an expected non-linear response of at least one of the loudspeaker and the amplifier and an expected linear response of at least one of the loudspeaker and the amplifier. A controller coupled to the audio processor and a control input of the audio processor may vary the operating parameters of the audio processor depending on the estimated distortion.