Acoustic Head Tracking via Cross-Correlation
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Solution Overview
Problem
Existing headtracking systems are limited by their sensitivity to environmental noise, require complex circuitry, and are not suitable for applications requiring minimal computing power and unobtrusive, affordable, and comfortable wear, especially in automotive rear seat entertainment systems where they fail to provide accurate spatial audio localization due to 'in-head localization' issues with headphones.
Innovation Solution
A method using a minimal setup of two microphones and two loudspeakers emitting test signals at different frequencies, employing cross-correlation and autocorrelation functions to calculate propagation times and rotation angles, ensuring insensitivity to noise and reflections, and allowing for two-dimensional localization within the passenger cell constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional headtracking systems use multiple sensors and complex circuitry to achieve accurate head position tracking, then measurement precision is improved, but device complexity increases and computing power requirements increase
Solution Approach 1:
The patent divides the headtracking function into two separate systems: a simple sensor system worn by the user that only detects head position, and a separate processing system that contains all the complex correlation algorithms and computing resources. This segmentation allows the wearable device to remain simple while achieving accurate tracking through sophisticated processing.
Solution Approach 2:
The patent introduces test signals as an intermediary medium between the loudspeakers and the microphones. These test signals serve as reference markers that enable the system to calculate propagation times and determine head position without requiring complex direct measurement circuitry. The test signals act as a mediator that simplifies the measurement process.
2Measurement precision
If headtracking systems use complex sensors and processing circuits to achieve accurate tracking, then measurement precision is improved, but the system becomes more sensitive to environmental noise and reflections
Solution Approach 1:
The patent changes the temporal parameters of the test signals, using impulse-shaped signals with specific duration and repetition rates. By carefully selecting these parameters, the system can distinguish the direct test signal from reflected signals and noise, as the correlation algorithm looks for matches within specific time windows that correspond to direct path propagation times.
Solution Approach 2:
The patent converts the potential harm of environmental noise and reflections into a benefit by using cross-correlation analysis. The correlation algorithm can distinguish between direct signals and reflected signals based on their arrival times, effectively using the time-domain separation to filter out harmful reflections and noise while maintaining accurate position tracking.
3Measurement precision
If headphones are used to provide spatial audio localization, then audio focusing on individual persons is improved, but in-head localization occurs preventing natural spatial perception
Solution Approach 1:
The patent implements a feedback loop where the headtracking system continuously monitors the user's head position and provides real-time feedback to the audio processing system. This feedback enables dynamic adjustment of the audio signals based on actual head orientation, maintaining natural spatial perception even when the user moves their head while wearing headphones.
Solution Approach 2:
The patent makes the audio system dynamic by continuously updating the spatial audio parameters based on real-time head position data. Instead of static audio routing, the system dynamically adjusts the audio signal characteristics according to the user's current head orientation, thereby eliminating the fixed in-head localization effect and creating the perception of natural spatial audio.
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 provides accurate and reliable head tracking with minimal computing power, resistance to noise, and compatibility with existing automotive audio systems, eliminating 'in-head localization' and enabling natural spatial audio perception with headphones.
Implementation Method 1
an impulse-shaped sonic signal is integrated by a transmitting converter into the measurement medium, and detected after crossing the measurement path by a reception converter. The sonic propagation time is the difference in time between the transmission process and the reception of the sonic signal at the reception point.
Data Source
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AI summary
System and method for tracking of a head comprising generating and radiating at least one acoustical test signal; receiving the radiated acoustical test signal(s) at two locations at the head under investigation and generating electrical measurement signals therefrom; and evaluating the two measurement signals for determining the position and/or angle of rotation ϕ from the measurement signals; said evaluation step comprises a cross power spectrum operation of the test signal(s) and the signals from the receivers in the frequency domain.