java调用巴赫沃兹高通，低通滤波

在安卓开发的时候有时间要对音频，振动等信号进行滤波，下面是一段音频信号经过高通滤波后和低通滤波后的效果

可以看到滤波效果是只过滤出需要频率的信号，将噪音去掉

下面是java代码

public class Filter {
    private static double rate = 0.000000001;
    private static Double[] audha = {1.0, -1.98388104166084, 0.984009917549517};
    private static Double[] audhb = {0.991972739802589, -1.98394547960518, 0.991972739802589};
    private static Double[] audla = {1.0,-7.12374475999005,22.2456381652698,-39.7699187284106,44.5164561572107,-31.9455283104170,14.3513710384153,-3.68998752786006,0.415714445797744};
    private static Double[] audlb = {1.87506157822703*rate,1.50004926258163*rate*10,5.25017241903569*rate*10,
            1.05003448380714*rate*100,1.31254310475892*rate*100,1.05003448380714*rate*100,5.25017241903569*rate*10,
            1.50004926258163*rate*10,1.87506157822703*rate};

    private static Double[] in;
    private static Double[] out;
    private static Double[] outData;

    public static Double[] highpass(Double[] signal) {
        return filter(signal, audha, audhb);
    }

    public static Double[] lowpass(Double[] signal) {
        return filter(signal, audla, audlb);
    }

    private static Double[] filter(Double[] signal, Double[] a, Double[] b) {
        in = new Double[b.length];
        out = new Double[a.length - 1];
        outData = new Double[signal.length];
        for (int i = 0; i < signal.length; i++) {
            System.arraycopy(in, 0, in, 1, in.length - 1);  //in[1]=in[0],in[2]=in[1]...
            in[0] = signal[i];
            //calculate y based on a and b coefficients
            //and in and out.
            Double y = 0.0;
            for (int j = 0; j < b.length; j++) {
                if (in[j] != null) {
                    y += b[j] * in[j];
                }
            }


            for (int j = 0; j < a.length - 1; j++) {
                if (out[j] != null) {
                    y -= a[j + 1] * out[j];
                }
            }

            //shift the out array
            System.arraycopy(out, 0, out, 1, out.length - 1);
            out[0] = y;
            outData[i] = y;
        }
        return outData;
    }
}

这里的audha，audhb，audla，audlb四个参数是怎么来的呢

我是从matlab代码得来的，看一下matlab的高低通滤波

function [dataOut,a,b]=lowpass(data,fs,f)
%低通滤波：滤除 f HZ以上的信号
[b,a] = butter(8,f/fs*2);
dataOut = filter(b,a,data);

function [dataOut,a,b]=highpass(data,fs,f)
%高通滤波
[b,a] = butter(2,f/fs*2,'high');
dataOut = filter(b,a,data);

使用，就会得到高通的参数a，b和低通的参数a，b。这里我使用的是11025HZ的频率，过滤掉20HZ以下的

[traindata,a,b]=highpass(traindata,11025,20);

就得到a，b

低通滤波同理，把得到的四个参数复制到java代码里面即可。

java代码调用传入数组即可得到滤波后的数组