A practical method to reduce a number of reference signals for the ANC system

We propose a practical method to reduce a number of reference signals for an active noise cancellation (ANC) system and the filter characteristics to generate the reduced number of reference signals, which maintain the original value of the coherence function. This method finds the number of independent noise sources and provides the filter characteristics based on SVD (singular value decomposition) of the power spectrum matrix of the reference signals. Then, we also use the multiple coherence function analysis to select dominant components in the reference signals. The method contributes greatly in reducing the number of reference signals for the ANC system that uses the large number of reference signals. We also discuss the characteristics of the filters that synthesizes the new set of reference signals. An experimental test is also performed to confirm the theory.