Virtual Microphone Signal Generation for Compact Surround Sound
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Solution Overview
Problem
Compact recording devices face challenges in simulating surround sound with fewer microphones due to size and processing restraints, leading to cumbersome calculations and crosstalk issues that degrade the directivity of directional microphones.
Innovation Solution
A system and method that converts intermediate audio signals into the frequency domain, calculates virtual microphone signals using Bark frequency-bands and cross-correlations, and applies cancellation signals to reduce crosstalk, allowing for efficient generation of surround sound signals with fewer intensive calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If five or more separate directional microphones are used for recording audio, then the directivity and surround sound quality are improved, but the device size and processing complexity increase
Solution Approach 1:
The patent creates virtual copies of directional microphone signals through mathematical processing. Instead of physically installing five or more directional microphones, the system uses a smaller number of physical microphones and generates virtual directional signals through signal processing algorithms, thereby achieving the directivity of multiple microphones without the corresponding increase in device size
Solution Approach 2:
The patent replaces the mechanical solution of using multiple physical directional microphones with a signal processing solution. By using mathematical operations on the signals from fewer microphones, the system achieves the same acoustic effect as multiple physical microphones would provide, substituting mechanical complexity with computational processing
2Adaptability or versatility
If intensive calculations are performed to produce surround channel playback from fewer microphones, then adaptability across different channel formats is improved, but processing power requirements and time consumption increase
Solution Approach 1:
The patent performs preliminary signal processing and pre-calculates the relationships between microphone signals and surround channel signals. By preparing the signal transformations in advance and establishing the mathematical relationships beforehand, the system reduces the computational burden during actual playback, enabling format flexibility without requiring excessive processing power at runtime
Solution Approach 2:
The patent changes the parameters of the audio signals through mathematical transformations, converting signals from the microphone domain to the surround channel domain. By manipulating signal parameters such as amplitude, phase, and frequency relationships through predefined transformation matrices, the system achieves adaptability across different channel formats with reduced computational complexity
3Device complexity
If weighted combinations of audio signals are used to simulate directional microphones, then device complexity is reduced, but channel crosstalk increases and directivity simulation deteriorates
Solution Approach 1:
The patent incorporates feedback mechanisms in the signal processing pipeline, where the generated virtual directional signals are compared with reference signals and the difference is used to adjust and refine the output. This feedback loop helps minimize channel crosstalk and improves the accuracy of directivity simulation, ensuring that the virtual microphone signals closely match the desired directional characteristics
Solution Approach 2:
The patent converts the potentially harmful effect of channel crosstalk into a beneficial feature by using it as information to refine the signal processing. The crosstalk between channels is analyzed and utilized to adjust the weighting coefficients and transformation parameters, thereby improving the overall directivity simulation accuracy while maintaining the benefit of reduced device complexity
Data Source
AI summary
A system and method for generating virtual microphone signals having a particular number and configuration for channel playback from an intermediate set of signals that were recorded in an initial format that is different from the channel playback format. In one embodiment, an initial set of intermediate are Bark-banded such that each intermediate signal may lead to a corresponding power spectral density (PSD) signal representative of the initial intermediate signal. Further, one may generate cross-correlations signals for each pair of intermediate signals. Next, from the PSDs and cross correlations, one may more efficiently calculate corresponding channel signals to be used for playback on respective channel speakers. Thus, the PSDs of each channel signal may be generated at chosen angles (as well as other design factors). Further, each channel signal may also be further modified with a corresponding cancellation signal that further enhances the resultant signal in each channel.