Abstract: More and more researchers have focused on analyzing the heart sound signals in computers. However, noise often appears in parts of heart sounds when they are recorded, therefore how to evaluate the noise level of the heart sound becomes an important problem. This paper suggests a noise evaluation index—quality index, which is defined on the cyclostationary property of the heart sounds. It can estimate the noise level accurately. If the heart sound signal acquired is too long, selecting the signal segments with larger quality index can pick out those which are less noisy, which can greatly reduce time of preprocessing, such as denoising. The quality index defined in this paper is suitable to all normal and abnormal heart sound signals, and no manual intervention is needed in the process of subsequence selection, therefore making this scheme useful in automatic analysis of heart sound signals.

Key words: heart sound signal, cyclostationary, noise evaluation index

摘要： 采用计算机来分析心音信号引起了越来越多的研究人员的关注，但是，心音信号在采集过程中常常会受到各种噪声的干扰，如何评价心音信号受噪声影响的程度就成为一个重要的问题。提出了一种基于循环平稳特性的心音信号噪声评价指标——质量因子，它能够准确地、定量地评估心音信号的噪声情况，即质量因子越大，信号受噪声的影响越小。如果实际采集的心音信号比较长，那么计算整个信号的质量因子，把质量因子最大的那一段心音信号取出来进行处理，这样可以大大减少去除噪声等预处理过程，节省了计算量和时间。所提出来的质量因子，对于正常和异常心音信号都适用，计算机完全可以自动计算，无需人工干预。

关键词: 心音信号, 循环平稳, 噪声评价指标