Acoustic Echo Cancellation Using Transducer Impedance
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Solution Overview
Problem
Existing acoustic echo cancelers in mobile devices are hindered by the nonlinearities of audio transducers, leading to reduced performance in echo cancellation, particularly at high volumes due to the mixture of linear and nonlinear components in echo signals.
Innovation Solution
An acoustic echo cancellation system that calculates impedance and generates an echo cancellation signal based on current and voltage inputs to predict coil velocity, allowing for the estimation and cancellation of nonlinear transducer responses without integrating coil position, thereby improving adaptive noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a typical acoustic echo canceler estimates only the linear acoustic impulse response, then the linear components are canceled, but the nonlinear components remain large and audible particularly at high volumes
Solution Approach 1:
The patent segments the echo signal into linear and nonlinear components, processing them separately. The linear impulse response is estimated through standard AEC, while nonlinear components are captured by recording the actual speaker output and microphone input, then combining both approaches to achieve complete echo cancellation including nonlinear distortions
Solution Approach 2:
The patent creates a copy of the speaker's actual nonlinear behavior by recording the relationship between speaker input signal and actual acoustic output. This copy is then used to generate compensation signals that replicate and cancel the nonlinear distortion components in real-time echo cancellation
2Ease of manufacture
If inexpensive low-quality loudspeakers are used in mobile devices, then device cost is reduced, but isolation from the audio device is poor leading to reduced echo cancellation performance
Solution Approach 1:
The system uses the inexpensive speaker's own characteristics to improve performance. By recording the actual nonlinear behavior of the specific speaker unit and using that recorded data to generate compensation signals, the system turns the speaker's inherent nonlinearities into known, compensatable factors rather than unknown errors
Solution Approach 2:
The patent implements feedback by continuously monitoring the relationship between speaker input and actual acoustic output, then using this feedback information to adjust and refine the nonlinear compensation signals, creating a closed-loop system that adapts to the specific speaker's characteristics
3Power
If the transducer is overdriven to achieve higher volume, then audio output is increased, but saturation effects distort sound in a nonlinear manner
Solution Approach 1:
The patent performs preliminary action by pre-characterizing the speaker's nonlinear behavior through recording the relationship between input and output signals before actual use. This pre-captured nonlinear profile is then applied in real-time to generate compensation signals that prevent saturation distortion from degrading audio quality at high volumes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the quality of echo cancellation by accurately predicting and canceling nonlinear responses, reducing processing complexity and improving the overall performance of echo cancellation in mobile devices.
Implementation Method 1
calculating an impedance of the audio speaker based, at least in part, on the current signal received at the current input node and the voltage signal received at the voltage input node
Implementation Method 2
predict a coil velocity of the transducer based on the transducer impedance
Data Source
AI summary
An acoustic echo cancellation (AEC) system within an audio playback system of an electronic device, such as a mobile phone, may calculate an estimation of an acoustic echo based on parameters describing the transducer reproducing the audio playback signals. Those parameters may include, for example, a resistance and/or inductance of the transducer and a current through and/or a voltage across the transducer. The acoustic echo cancellation system may predict, for example, a coil velocity of the transducer based on the transducer impedance. Then, an echo may be estimated using the predicted coil velocity. That estimated echo may be output to the transducer to cancel echo in the playback signal. Additionally, that estimated echo may be used to predict nonlinearities in the transducer output and an appropriate signal generated to cancel nonlinear behavior.