一.介紹
前段時間接到一個項目：偵聽調頻廣播，實現頻譜、瀑布圖顯示，話音播放、存儲及語音時域圖繪制。其中，話音播放時感覺其噪聲很大，必須對其降噪。在C#網上搜索了很多關于C#降噪的，沒搜到。利用MATLAB編寫降噪函數，并生成dll，但是發現調用Matlab的dll挺耗時的，所以不采用這種方式。于是我仿MATLAB降噪的函數，寫出了C#版降噪函數。播放的話音明顯實現了，但是其中有一個bug，就是降噪后會有噠噠噠的聲音，找了好久沒找到原因。如果能找出bug的兄弟，望告知一下。
二.代碼
1.低通濾波函數

// 說明：MATLAB轉C#函數 private double[,] Lowpass_T(Int16[] Indata, int Len) {//定義濾波結果的數組，為二位數組，Len行，1列double[,] Filterdata = new double[Len, 1];int LowpassLen = 67;//濾波器系數double[] LowpassBuf_1 = new double[] {-0.0002297245116924, -0.001272528501084, -0.003334224714919, -0.006360776347928,- 0.009289045067669, -0.01048313976472, -0.008492643648294, -0.003258372951239,0.003268094048695, 0.007734987474474, 0.007277665725254, 0.001653277578148,- 0.005926998028789, -0.01029359540466, -0.007644782129877, 0.001353382650881,0.01111257398261, 0.01429420479649, 0.007026067120628, -0.007359476125338,- 0.01926144120085, -0.01876047817833, -0.003187318370228, 0.01905162190054,0.03211612756329, 0.02284966783339, -0.008518122931876, -0.04454921689637,- 0.05771153561822, -0.02573624712695, 0.05336790092737, 0.1561693966912,0.2429077783893, 0.2767802107121, 0.2429077783893, 0.1561693966912,0.05336790092737, -0.02573624712695, -0.05771153561822, -0.04454921689637,- 0.008518122931876, 0.02284966783339, 0.03211612756329, 0.01905162190054,- 0.003187318370228, -0.01876047817833, -0.01926144120085, -0.007359476125338,0.007026067120628, 0.01429420479649, 0.01111257398261, 0.001353382650881,- 0.007644782129877, -0.01029359540466, -0.005926998028789, 0.001653277578148,0.007277665725254, 0.007734987474474, 0.003268094048695, -0.003258372951239,- 0.008492643648294, -0.01048313976472, -0.009289045067669, -0.006360776347928,- 0.003334224714919, -0.001272528501084, -0.0002297245116924};//將濾波系數LowpassBuf_1轉化為二位數組double[,] LowpassBuf = new double[LowpassBuf_1.Length, 1];for (int i = 0; i < LowpassBuf_1.Length; i++){LowpassBuf[i, 0] = LowpassBuf_1[i];}//創建緩存變量Int16[] m_pData = new Int16[Len];//計算濾波for (int k = 0; k < Len; k++){for (int i = LowpassLen - 1; i > 0; i--){m_pData[i] = m_pData[i - 1];}m_pData[0] = Indata[k];double Temp = 0;for (int i = 0; i < LowpassLen; i++){Temp = Temp + LowpassBuf[i, 0] * m_pData[i] * 2;}//保存為Len行1列的數組Filterdata[k, 0] = Temp;}return Filterdata; }

2.降噪函數

// 說明：MATLAB轉C#函數private double[] NoiseReduction_T(Int16[] Indata, int Len, int Thre){// 定義返回數組，和輸入數據長度等長double[] Outdata = new double[Len];// 濾波器double[,] Filterdata = Lowpass_T(Indata, Len);// 設置窗口長度int Win = 256;for (int i = 0; i < Len / Win; i++){//將數據按Win長度分段處理double[] Windata = new double[Win];for (int m = 0; m < Win; m++){Windata[m] = Filterdata[i * Win + m, 0];}int sum = 0;//判斷每個Win長度數據中小于閾值Thre的數據個數for (int j = 0; j < Win; j++){if (Windata[j] < Thre){sum = sum + 1;}}// 如果大于250個 則認定為噪聲 并對這段Win長度數據歸零 如果不是噪聲 往后延續15段保證聲音連續if (sum > 250){for (int m = 0; m < Win; m++){Filterdata[i * Win + m, 0] = 0;}}else{i = i + 15;}}for (int i = 0; i < Len; i++){Outdata[i] = Filterdata[i, 0];}return Outdata;}

3.降噪處理函數

// 自定義函數：降噪處理public byte[] DeNoise(byte[] sData, int nLen, int Fs, int Thre){// 長度：8192byte[] result = new byte[nLen];// 長度：4096Int16[] buffer_s = new Int16[nLen / 2];for (int i = 0; i < buffer_s.Length; i++){// 兩個字節轉為short（低位在前，高位在后）buffer_s[i] = BitConverter.ToInt16(new byte[] {sData[2 * i], sData[2 * i + 1] }, 0);}// 降噪處理：輸入（長度：4096）Int16[] array_In = buffer_s;// 降噪處理：輸出（長度：4096）double[] array_Out = NoiseReduction_T(array_In, buffer_s.Length, Thre);// 取出最后一個值（即索引為4096的值）for (int i = 0; i < array_Out.Length - 1; i++){sbyte[] tmp = TypeCast(array_Out[i]);result[i * 2] = (byte)tmp[0]; // 低位在前result[i * 2 + 1] = (byte)tmp[1]; // 高位在后}return result;}

4.調用降噪處理函數

//降噪byte[] bytesDst = bytesSrc; bytesDst = m_NoiseReduct.DeNoise(bytesSrc, bytesSrc.Length, 31500, m_nThresholdDeNoise);

總結

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