WINCE音量調節的實現

wince音量調節的實現

劉啟明 2010-5-8

pulong pdwgain = (pulong)dwparam1;

if (pstreamcontext)

*pdwgain = pstreamcontext->getgain();

else

// handle device gain in hardware

//*pdwgain = g_phwcontext->getoutputgain();//沒有硬體音量調節支援

// handle device gain in software

devicecontext *pdevicecontext = g_phwcontext->getoutputdevicecontext(udeviceid);//軟音量獲取

*pdwgain = pdevicecontext->getgain();

dwret = mmsyserr_noerror;

break;

case wodm_setvolume://音量設定.

long dwgain = dwparam1;

if (pstreamcontext)//如果存在音訊流，則這裡調節音訊流音量

break;

m_fxpgain = mapgain(m_dwgain);//m_fxpgain儲存音訊流的音量大小

}dword totalgain = gain & 0xffff;

dword secondarygain = m_pdevicecontext->getsecondarygainlimit(m_secondarygainclass) & 0xffff;

//retailmsg(1,(_t("mapgain volume set gain = 0x%x/n"),gain));//lqm test.

if (m_secondarygainclass < secondarydevicegainclassmax)

dword devicegain = m_pdevicecontext->getgain() & 0xffff;

retailmsg(1,(_t("gain=0x%x,devicegain=0x%x/n"),gain,devicegain));//lqm test.

totalgain *= devicegain;

totalgain += 0xffff; // round up

totalgain >>= 16; // shift to lowest 16 bits

totalgain *= secondarygain;

totalgain += 0xffff; // round up

totalgain >>= 16; // shift to lowest 16 bits

retailmsg(1,(_t("mapgain volume set totalgain = 0x%x/n"),totalgain));//lqm test.

// special case 0 as totally muted

if (totalgain==0)

return 0;

// convert to index into table

dword index = 63 - (totalgain>>10);

retailmsg(1,(_t("mapgain index = 0x%x/n"),index));//lqm test.

//index = 50;//lqm added for test.10-05-06

return gainmap[index];

傳入引數gain即上面提到的m_dwgain，該引數為32位暫存器，高16位和低16位分別存放左右聲道。由於一般情況下左右聲道的音量都是一樣的，故程式中只取了低16位。

totalgain是devicegain和m_dwgain的乘積，然後右移16位得到的。其實就是totalgain=devicegain*m_dwgain/最高音量，如果把devicegain/最高音量，用百分比來算的話，就很更容易理解了，那麼最後的公式就變成totalgain=devicegain*系統音量百分比。那麼這裡就解釋了系統音量是如何限制流音量的疑問。

最終通過乙個索引求出對應音量的權值，再通過音量表設定音量。可以看到index = 63 - (totalgain>>10);index在0到63的範圍內。返回的gainmap表如下：

const dword gainmap =

0x10000, // 0: 0.000000 db

0xec77, // 1: -1.587302 db

0xda6d, // 2: -3.174603 db

0xc9c2, // 3: -4.761905 db

0xba5d, // 4: -6.349206 db

0xac25, // 5: -7.936508 db

0x9f03, // 6: -9.523810 db

0x92e1, // 7: -11.111111 db

0x87ac, // 8: -12.698413 db

0x7d52, // 9: -14.285714 db

0x73c2, // 10: -15.873016 db

0x6aed, // 11: -17.460317 db

0x62c5, // 12: -19.047619 db

0x5b3b, // 13: -20.634921 db

0x5445, // 14: -22.222222 db

0x4dd7, // 15: -23.809524 db

0x47e7, // 16: -25.396825 db

0x426b, // 17: -26.984127 db

0x3d59, // 18: -28.571429 db

0x38ab, // 19: -30.158730 db

0x3458, // 20: -31.746032 db

0x305a, // 21: -33.333333 db

0x2ca9, // 22: -34.920635 db

0x2941, // 23: -36.507937 db

0x261b, // 24: -38.095238 db

0x2333, // 25: -39.682540 db

0x2083, // 26: -41.269841 db

0x1e08, // 27: -42.857143 db

0x1bbe, // 28: -44.444444 db

0x19a0, // 29: -46.031746 db

0x17ab, // 30: -47.619048 db

0x15dd, // 31: -49.206349 db

0x1432, // 32: -50.793651 db

0x12a7, // 33: -52.380952 db

0x113b, // 34: -53.968254 db

0x0fea, // 35: -55.555556 db

0x0eb3, // 36: -57.142857 db

0x0d94, // 37: -58.730159 db

0x0c8b, // 38: -60.317460 db

0x0b96, // 39: -61.904762 db

0x0ab4, // 40: -63.492063 db

0x09e3, // 41: -65.079365 db

0x0921, // 42: -66.666667 db

0x086f, // 43: -68.253968 db

0x07ca, // 44: -69.841270 db

0x0732, // 45: -71.428571 db

0x06a6, // 46: -73.015873 db

0x0624, // 47: -74.603175 db

0x05ac, // 48: -76.190476 db

0x053d, // 49: -77.777778 db

0x04d7, // 50: -79.365079 db

0x0478, // 51: -80.952381 db

0x0421, // 52: -82.539683 db

0x03d0, // 53: -84.126984 db

0x0386, // 54: -85.714286 db

0x0341, // 55: -87.301587 db

0x0301, // 56: -88.888889 db

0x02c6, // 57: -90.476190 db

0x0290, // 58: -92.063492 db

0x025e, // 59: -93.650794 db

0x0230, // 60: -95.238095 db

0x0205, // 61: -96.825397 db

0x01de, // 62: -98.412698 db

0x01b9, // 63: -100.000000 db

這就是軟音量設定最終呼叫的音量配置表。具體它是如何通過這個表來實現軟音量設定的，還需要認真研究，難道通過i2s送到音訊晶元的數碼訊號裡面已經帶有音量資料？不過到這裡，軟的音量調節功能已經實現了，詳細的原理有空再仔細研究

WINCE音量調節的實現

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WINCE音量調節的實現

WINCE音量調節（適用於智慧型裝置）

C 調節PCM音量

音量調節流程

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