Analog active control of acoustic noise at a virtual location

In this brief, an analog virtual microphone control system in application to noise reduction for a phone is designed. It aims at generating a zone of quiet at a virtual microphone location corresponding to the eardrum. Such location is different than the real microphone location. The idea of the control system is based on the assumption that the primary acoustic noise is the same at these two locations. The first constraint is formulated to guarantee a sufficient stability margin. Another constraint protects against excessive noise reinforcement for any frequency. Controller parameters are found by solving the optimization problem. Due to its high nonlinearity the exhaustive search method is used. It follows a preliminary analysis of the solution space. Additionally, a feedforward filter compensating for influence of the control system on the transmitted speech is designed. The overall control system is implemented using chips with switched capacitors, what makes the tuning and maintenance easy. The system is verified by means of simulations and real-world experiments. It is shown that road noise is satisfactorily reduced. Both measurement results and subjective impressions confirm that the system meets the requirements.