Ambisonic Encoding with FIR Filter Directivity Optimization
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Solution Overview
Problem
Existing methods for recording 360° sound signals face challenges in accurately reproducing spatial sound due to diffraction phenomena caused by obstacles, especially when using arrays of microphones, which results in frequency-dependent delays and phase shifts, limiting faithful sound reproduction.
Innovation Solution
A method involving the synchronous acquisition of sound signals by omnidirectional microphones, followed by directivity optimization using FIR filters and correction with IIR filters to create an ambisonics format, allowing for the compensation of artefacts and accurate spatial sound reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a reduced number of omnidirectional microphones is used, then costs are reduced, but faithful reproduction of sound signals is compromised due to diffraction phenomena causing frequency-dependent delays
Solution Approach 1:
The patent applies frequency-dependent delay parameters that vary according to frequency, rather than using a single fixed delay. This allows the system to compensate for diffraction effects at different frequencies, maintaining accurate sound reproduction while using fewer microphones. The delay parameter is changed dynamically based on frequency analysis of the received signal.
Solution Approach 2:
The system performs preliminary analysis of the received sound signal to determine diffraction characteristics before applying the frequency-dependent delay compensation. By analyzing the signal first and then applying appropriate compensation parameters, the system pre-corrects for expected diffraction effects, enabling accurate reproduction with reduced microphone arrays.
2Device complexity
If a fixed delay is applied to compensate for obstacle diffraction, then processing is simplified, but frequency-dependent phase shifts cannot be corrected
Solution Approach 1:
The patent transitions from static fixed delay compensation to dynamic frequency-dependent delay compensation. The delay parameter becomes dynamic, varying with frequency based on the spectral content of the received signal. This dynamic approach maintains computational feasibility while significantly improving phase accuracy across different frequencies.
Solution Approach 2:
The system performs preliminary frequency analysis of the received signal to determine appropriate delay parameters for different frequency components. This preliminary action enables the system to select optimal delay values before applying compensation, balancing processing complexity with phase accuracy requirements.
Data Source
AI summary
A method for processing a sound signal including synchronously acquiring an input sound signal Sinput by means of at least two omnidirectional microphones, encoding the input sound signal Sentréeinput in a sound data D format of the ambisonics type of order R, R being a natural number greater than or equal to one, the encoding step including a directivity optimisation sub-step carried out by means of filters of the Finite Impulse Response filter type. Each of the signals acquired by the microphones is filtered during the directivity optimisation sub-step by a FIR filter, then subtracted from an unfiltered version of each of the other signals in order to obtain N enhanced signals. The present invention also relates to a system for processing the sound signal.