Noise threatens human’s health both physically and psychologically. On the basis of insulation and absorption of sound, traditional passive method sustains poor performance in low frequency. By comparison, active noise control (ANC) technology shows excellent low-frequency properties and is widely investigated. 

In the narrowband ANC system where the noise signal is a tonal one, it is very important to track the frequencies of the noise signal, especially when these frequencies change over time. However, conventional algorithms have some disadvantages, such as biased resultsand high computational burden.  

In order to track the noise tones, a research team led by Prof. YANG Jun from the Institute of Acoustics (IOA) of Chinese Academy of Sciences proposed a new frequency estimation algorithm based on a parallel notch filter structure. The study was published in Signal Processing. 

When combining the advantages of conventional algorithms and avoiding their weaknesses, the parallel notch filter structure presents high accuracy and low complexity. 

The researchers first conducted the theoretical performance in detail in both the tracking accuracy of the frequency estimation and the noise reduction value of the active noise control system. The results of the performance analysis were visual and accurate.  

Then they provided simulations to verify the performance analysis of the frequency estimation. Experiments were conducted in an air pipe active noise control system (Figure 1). 

Figure 1. Narrowband active noise control system. (Image by WANG Han) 

The simulations and experiment results revealed that the new algorithm had good performance. "Now, we can predict the noise reduction value accurately in a system with frequency mismatch or frequency estimation algorithm," said YANG.  

The research was supported by the national natural science foundation of China and Youth Innovation Promotion Association, Chinese Academy of Sciences.