Microphone Array Using Semi-Blind Source Separation
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Solution Overview
Problem
Microphone arrays in portable devices face limitations in sound resolution due to the practical lower limit of microphone spacing, which restricts the ability to accurately determine sound source direction and location, especially with inexpensive microphones that can only respond to frequencies up to 16 kHz, requiring microphones to be at least 4 cm apart, making them too large for many devices.
Innovation Solution
The implementation of semi-blind source separation and fractional delays in microphone arrays allows for optimized signal processing, enabling better sound source separation and noise reduction by determining a listening direction and applying fractional delays to improve the signal-to-noise ratio, effectively overcoming the limitations of microphone spacing and frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If microphone spacing is increased to improve sound resolution and direction detection, then measurement precision is improved, but device volume increases making it unsuitable for portable devices
Solution Approach 1:
The patent changes the frequency parameter by using ultrasonic frequencies (above 20 kHz) instead of audible frequencies. This allows the microphone spacing to be reduced to less than 1 cm while maintaining adequate time delay for direction detection, as the shorter wavelength of ultrasonic frequencies enables smaller spacing while still providing measurable time differences of arrival.
2Volume of moving object
If microphone spacing is reduced to decrease device volume, then device volume is reduced, but measurement precision deteriorates due to insufficient time delay between microphone signals
Solution Approach 1:
The patent applies ultrasonic frequencies to change the wavelength parameter, allowing smaller microphone spacing while maintaining sufficient time delay for accurate direction detection. The high frequency enables the system to achieve both compact size and measurement precision.
3Volume of moving object
If ultrasonic frequencies are used to enable smaller microphone spacing, then device volume is reduced, but manufacturing precision requirements increase due to tighter spacing tolerances
Solution Approach 1:
The patent replaces mechanical positioning with electronic signal processing. A virtual microphone is created through digital signal manipulation, where the position of the virtual microphone can be adjusted electronically without physical constraints. This eliminates the need for precise mechanical spacing while maintaining the benefits of ultrasonic frequency operation.
Data Source
AI summary
Methods and apparatus for signal processing are disclosed. A discrete time domain input signal xm(t) may be produced from an array of microphones M0 . . . MM. A listening direction may be determined for the microphone array. The listening direction is used in a semi-blind source separation to select the finite impulse response filter coefficients b0, b1 . . . , bN to separate out different sound sources from input signal xm(t). One or more fractional delays may optionally be applied to selected input signals xm(t) other than an input signal x0(t) from a reference microphone M0. Each fractional delay may be selected to optimize a signal to noise ratio of a discrete time domain output signal y(t) from the microphone array. The fractional delays may be selected to such that a signal from the reference microphone M0 is first in time relative to signals from the other microphone(s) of the array. A fractional time delay Δ may optionally be introduced into an output signal y(t) so that: y(t+Δ)=x(t+Δ)*b0+x(t−1+Δ)*b1+x(t−2+Δ)*b2+ . . . +x(t−N+Δ)bN, where Δ is between zero and ±1.