重庆大学硕士学位论文心音信号的第一心音幅值提取算法的研究姓名：吕佶申请学位级别：硕士专业：信号与信息处理指导教师：朱冰莲20060401摘要心音检测为评估心脏和血管的功能与状态提供了低廉的非介入性的方法。
第一心音的幅值是心脏收缩能力的标准度量，心音图(PCG)可以用于心力储备的研究。
为此，需要消除PCG信号中的噪声，并用分段算法定位第一心音。
心音信号采集过程中会引入多种噪声，而这些噪声在频域的分布并不总是与心音信号的分布分离的，故传统的频域滤波方法的使用就受到了限制。
本文先介绍了主要的几种小波去噪方法，然后详细讨论了小波阈值收缩去噪方法，探讨了最影响其性能的分解尺度、阈值方法和阈值函数等问题。
在对仿真信号和真实信号去噪实验的基础上，选择了适当的去噪方案。
心音信号是一种非平稳的信号，而时频分析是处理这一类信号的有效方法。
本文简要的介绍了常用的时频分析方法，重点介绍了S变换方法及其离散算法。
通过考查几种时频分析得到的心音信号谱图和包络的性能，说明S变换是心音分析的有效方法。
心音分段采用了包络阈值方法。
提取包络使用了S变换方法，首先需要确定S 变换的分析窗口长度。
通过对比不同窗长的S变换的谱图性能和包络性能，最终确定了这一长度。
然后应用心脏生理特征参数和阈值方法对第一心音进行了定位。
实验表明，该方法是准确而有效的。
算法部分用标准C++实现，结果的图形表示部分则用Java实现。
首先设计了处理声音文件的类，然后通过正向抽取和逆向插值滤波器实现了小波阈值收缩去噪方法，利用C++标准库的算法缩短了其中中位数查找过程的时间。
使用FFTW 库实现S变换中的FFT和IFFT运算，提高计算S变换的性能。
实现时还考虑了高精度计时和移植性等问题。
关键词：心音，小波去噪，时频分析，S变换，心音识别ABSTRACTExamination of heart sound provides people with a cheap and non-invasive method to evaluate the function and status of heart and blood vessel.The amplitude of first heart sound is a normal measurement of cardiac contractility,and phonocardiogram(PCG) can be used in the study of cardiac contractility reserve.To achieve this,noise in the PCG signal should be removed,and a segmentation method should be used to locate the first heart sound.Various kinds of noises are introduced in the acquisition of heart sound signal.The distribution of noises in the frequency domain,however,is not always separate from that of heart sound signal.Thus,the use of traditional frequency domain filtering methods is limited.Several wavelet denoise methods are introduced,the waveshrink denoise method is discussed in detail later.The problem of decomposition scale, thresholding method and thresholding function are discussed.Appropriate denoise solution is selected based on the denoising experiment on simulated and actual signal.Heart sound signal is non-stationary signal,and time-frequency analysis is effective method to process this kind of monly used time-frequency analyses are introduced,S Transform and its discrete algorithm are emphasized.The review on the performance of spectrogram and envelope from several time-frequency analyses shows S Transform is an efficient method in heart sound analysis.The envelop-threshold method is used to segment the heart sound.S Transform is used to extract the envelope,and the length of analyzing window of S Transform needs to be defined.The length is set after the performance comparison of spectrogram and envelope from various window lengths.Then,physiological parameters of heart feature and threshold method are used to locate the first heart sound.Experiments show that this method is efficient and accurate.The algorithm is implemented in standard C++,and the graphic result representation is implemented in Java.Firstly,the sound file processing class is implemented.Then,the waveshrink denoise method is implemented with the help of forward decimation and backward interpolation filter.The algorithm provided in C++ standard library is utilized to shorten the time of median finding process.The FFTW library is exploited to implement the FFT and IFFT operation in S Transform,as a result, the performance of S Transform is improved.Precise timing and portability are alsotaken into consideration in the implementation of this algorithm.Keywords:Heart Sound,Time-Frequency Analysis,Wavelet denoising,S Transform Phonocardiogram Recognition1绪论1.1心音生理心动周期中，心肌收缩、瓣膜启闭、血液加速度和减速度对心血管壁的加压和减压作用以及形成的涡流等因素引起的机械振动，可通过周围组织传递到胸壁；如果将听诊器放在胸壁某些部位，就可以听到声音，称为心音。
