Android - 改變PCM數據音量大小

 

int db = 6; // 範圍：+30(最大聲) ~ 0(原始音量) ~ -96(最小聲)，Step：2
private double factor = Math.pow(10, (double)db/20); // 分貝公式 y = 20 * log10(x)

// 取得 16bit 採樣率的完整數據
private short getShort(byte[] data, int start) {
    return (short)((data[start] & 0xFF) | ((data[start+1] << 8) & 0xFF00));
}

/* 調整 PCM 數據音量
 * pData：原始音頻數據
 * nLen：原始音頻數據長度
 * data2：轉換後新音頻數據
 * nBitsPerSample：採樣率
 * multiple：表示增益值 (需代入公式計算結果，在這裡即是 factor)
 */
public int amplifyPCMData(byte[] pData, int nLen, byte[] data2, int nBitsPerSample, float multiple)
{
    int nCur = 0;
    float pcmval;
    if (nBitsPerSample == 16) {
        short volum;
        while (nCur < nLen) {
            volum = getShort(pData, nCur);
            // volum <<= 1;
            // volum = (short)(volum * multiple);
            pcmval = (volum * multiple);
            if(volum < -32768)
                volum = -32768;
            else if(volum > 32767)
                volum = 32767;
            else
                volum = (short)pcmval;
            data2[nCur]   = (byte)( volum       & 0xFF);
            data2[nCur+1] = (byte)((volum >> 8) & 0xFF);
            nCur += 2;
        }
    } else if(nBitsPerSample == 8) {
        byte volum;
        while (nCur < nLen) {
            volum = pData[nCur] & 0xFF;
            pcmval = (volum * multiple);
            if(volum < -127)
                volum = -127;
            else if(volum > 128)
                volum = 128;
            else
                volum = (byte)(pcmval);
            data2[nCur]   = (byte)(volum & 0xFF);
            nCur++;
        }
    }
    return 0;
}

參考：

[1] https://blog.csdn.net/mai763727999/article/details/106048905

[2] https://www.jianshu.com/p/50c697bec409

[3] http://blog.jianchihu.net/pcm-vol-control-advance.html