Single-Loudspeaker Otoacoustic Measurement Without Intermodulation Distortion
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Solution Overview
Problem
Conventional otoacoustic emission (OAE) measurement devices with two loudspeakers suffer from intermodulation distortions (IMDs) due to the non-linearity of the loudspeakers, which interfere with accurate OAE measurements, especially in compact devices like earbuds, requiring complex signal processing and calibration.
Innovation Solution
Using a single loudspeaker to alternately output two audio frequencies with minimal temporal overlap or gaps, allowing the cochlear hairs to oscillate at both frequencies simultaneously, thereby eliminating IMDs and enabling accurate otoacoustic emission measurement without additional signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two loudspeakers are used simultaneously to output two audio frequencies for OAE measurement, then the measurement can be performed according to conventional DPOAE method, but intermodulation distortions (IMDs) occur due to non-linearity of the loudspeakers, interfering with accurate measurements
Solution Approach 1:
The patent divides the simultaneous output of two audio frequencies into alternating sequential output. Instead of playing both frequencies at the same time through two loudspeakers, the system outputs the first audio frequency during a first time interval and the second audio frequency during a second time interval, thereby eliminating intermodulation distortions while still enabling DPOAE measurement through the cochlear non-linearity.
Solution Approach 2:
The patent employs periodic alternating output of two audio frequencies with specific timing intervals. The first audio frequency is output during a first time interval, followed by the second audio frequency during a second time interval, creating a periodic stimulation pattern that allows the cochlear hairs to oscillate at both frequencies and generate distortion products without loudspeaker-induced IMDs.
2Device complexity
If a single loudspeaker is used to output two audio frequencies simultaneously, then device complexity is reduced and form factor is smaller, but intermodulation distortions occur due to loudspeaker non-linearity
Solution Approach 1:
The patent segments the audio output in time rather than using multiple spatial channels. A single loudspeaker alternates between outputting the first audio frequency and the second audio frequency in different time intervals, eliminating the need for two simultaneous loudspeaker outputs while avoiding intermodulation distortions that would occur with simultaneous playback.
Solution Approach 2:
The single loudspeaker is driven with a periodic alternating signal pattern, outputting the first audio frequency during a first time interval and the second audio frequency during a second time interval. This periodic action allows the cochlear system to process both frequencies and generate distortion products without the loudspeaker itself producing intermodulation distortions.
3Measurement precision
If complex signal processing and calibration are applied to compensate for loudspeaker non-linearity, then measurement accuracy can be maintained, but device operation becomes more complex and time-consuming
Solution Approach 1:
The patent extracts and eliminates the source of intermodulation distortions by removing the need for simultaneous multi-frequency output through a single non-linear loudspeaker. By using alternating sequential output, the system eliminates the harmful non-linear interactions that would require complex signal processing and calibration to compensate, achieving accurate measurements with simpler operation.
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 method allows for more efficient, accurate, and faster OAE measurements in devices with a single loudspeaker, reducing the need for calibration and enabling a wider range of devices, including earphones and headphones, while maintaining a smaller form factor.
Implementation Method 1
causing alternating output of a first audio content and a second audio content, the first audio content comprising a first frequency and the second audio content comprising a different second frequency
Implementation Method 2
allowing the cochlear hairs to oscillate at both frequencies simultaneously
Implementation Method 3
Otoacoustic emissions (OAEs) are weak acoustic signals that are emitted from within the inner ear, from hairs of the cochlear such as the outer hair cells
Data Source
AI summary
According to various, but not necessarily all, examples there is provided an apparatus comprising: means for causing alternating output of a first audio content and a second audio content, the first audio content comprising a first frequency and the second audio content comprising a different second frequency; and means for receiving, responsive to output of the first audio content and the second audio content, an audio signal indicative of otoacoustic emissions.