C++ 調節PCM音頻音量大小

在用解碼器解碼音頻數據得到PCM音頻數據塊之后，可以在將數據送給聲卡播放之前調節其音量大小，具體的實現函數如下：

 

void RaiseVolume(char* buf, UINT32 size, UINT32 uRepeat, double vol)//buf為需要調節音量的音頻數據塊首地址指針，size為長度，uRepeat為重復次數，通常設為1，vol為增益倍數,可以小於1
{
    if (!size)
    {
        return;
    }
    for (int i = 0; i < size;)
    {
        signed long minData = -0x8000; //如果是8bit編碼這里變成-0x80
        signed long maxData = 0x7FFF;//如果是8bit編碼這里變成0xFF

        signed short wData = buf[i + 1];
        wData = MAKEWORD(buf[i], buf[i + 1]);
        signed long dwData = wData;

        for (int j = 0; j < uRepeat; j++)
        {
            dwData = dwData * vol;
            if (dwData < -0x8000)
            {
                dwData = -0x8000;
            }
            else if (dwData > 0x7FFF)
            {
                dwData = 0x7FFF;
            }
        }
        wData = LOWORD(dwData);
        buf[i] = LOBYTE(wData);
        buf[i + 1] = HIBYTE(wData);
        i += 2;
    }
}