Audio 的一些小笔记

1.在做项目的过程中，对于volume 我们有一个volume curve，就是 0~63 step，每个step对应一个dB值，例如0step对应-90dB, 63 step对应0dB。关于这个0dB，是由客户规定的，最大的输出是9V,20W,阻抗4Ω。dB一般是负值，dBa是由分贝仪测出来的，dBa有一套专门的标准来测

2.Balance(左右) 和 Fader(前后)是用来调节左右前后音量的， 调节Balance,对左边或者邮编的dB进行减少，Fader调前后，可以见下图

3.Loudness,对于当前音量，有一个低频/高频的音量补偿，直接上代码,

 ;
 /*take care of this value, volume table boost 18db for each step,
 so when calculate the volume table + LoudnessOffset, need
 attentuate 18db, so define the init value to -18*/
 ;
 static float OffsetPoints[CalNofPoints] = {0.0F, -10.0F, -20.0F, -30.0F, -40.0F, -50.0F, -60.0F, -70.0F,-80.0F, -90.0F, -90.0F};
 static float BassBoostValues[CalNofPoints] = {0.0F, 0.0F, 0.0F, 2.0F, 5.0F, 6.0F, 7.0F, 12.0F, 13.5F, 15.0F, 15.0F};
 static float BassFilterFrequence[CalNofPoints] = {80.0F, 80.0F, 80.0F, 80.0F, 100.0F, 200.0F, 250.0F, 350.0F, 400.0F, 400.0F, 400.0F};
 static float TrebleBoostValues[CalNofPoints] = {0.0F, 0.0F, 0.0F, 1.0F, 1.5F, 2.5F, 3.5F, 4.0F, 4.5F, 5.0F, 5.0F};
 static float TrebleFilterFrequence[CalNofPoints] = {12000.0F, 12000.0F, 12000.0F, 12000.0F, 12000.0F, 11000.0F, 10000.0F, 9000.0F, 8000.0F, 7000.0F, 7000.0F};

 float interpolate(float const x, uint_t const nof, float const xValues[], float const yValues[])//return y
 {
     float yRetval = 0.0F;
     //yValues are expected to be constant rising or falling
     //nof at least 2 otherwise there is nothing to interpolate
     <=nof)
     {
         uint_t ;
         ] < xValues[last];
         //check lower limit
         ]))
             || ((!rising) && (x > xValues[]))
             )
         {
             yRetval = yValues[];
         }
         //check upper limit
         else if (   ( (rising) && (x > xValues[last]))
             || ((!rising) && (x < xValues[last]))
             )
         {
             yRetval = yValues[last];
         }
         else//interpolate
         {
             //find index for x value
             uint_t index = ;
             ;i<last;i++)
             {
                 ]) )
                     ||( (!rising) && (xValues[i] >= x) &&(x >= xValues[i+]) )
                     )
                 {
                     index = i;
                     break;
                 }
             }
             //interpolate
             ];
             ];
             //check xDiff not 0
             if (fabs(xDiff) <= FLT_EPSILON)
             {
                 yRetval = yValues[index];
             }
             else//xDiff not 0 -> calculate y
             {
                 const float gradient = yDiff / xDiff;
                 const float yOffset = (x-xValues[index]) * gradient;
                 yRetval = yValues[index] + yOffset;
             }
         }
     }//check nof
     return yRetval;
 }

 bool_t CavDiranaRoutingCfg::getLoudnessCurveBoost(uint16_t filterID, uint16_t cfgID, float volume, float& loudnessBoost) const
 {
     bool_t retval = true;
     if(m_isLoudnessEnable == true)
     {
         ;
         EFilterID filtertype = static_cast<EFilterID>(filterID);
         loudnessBoost = ;

         //volume -> loudnessBoost
         OverallOffset = LoudnessOffset + volume;
         if (filtertype == FILTER_LOUDNESS_BASS)
         {
             loudnessBoost = interpolate(OverallOffset, CalNofPoints, OffsetPoints, BassBoostValues);
         }
         else if (filtertype == FILTER_LOUDNESS_TREBLE)
         {
             loudnessBoost = interpolate(OverallOffset, CalNofPoints, OffsetPoints, TrebleBoostValues);
         }
     }
     else
     {
         retval = false;
     }

     return retval;
 }

 bool_t CavDiranaRoutingCfg::getLoudnessCurveFilterPrm(uint16_t filterID, uint16_t cfgID, float volume, float& frequency, float& quality) const
 {
     bool_t retval = true;
     if(m_isLoudnessEnable == true)
     {
         ;
         EFilterID filtertype = static_cast<EFilterID>(filterID);
         quality = ;
         frequency = ;

         //volume -> bass filterprm
         OverallOffset = LoudnessOffset + volume;
         if (filtertype == FILTER_LOUDNESS_BASS)
         {
             frequency = interpolate(OverallOffset, CalNofPoints, OffsetPoints, BassFilterFrequence);
         }
         else if (filtertype == FILTER_LOUDNESS_TREBLE)
         {
             frequency = interpolate(OverallOffset, CalNofPoints, OffsetPoints, TrebleFilterFrequence);
         }
     }
     else
     {
         retval = false;
     }

     return retval;
 }

4.Adjustable Bass, Midrange, and Treble tone controls. 是对低频中频高频的一个调节

The bass tone control shall have the following characteristics: 
fcenter = 80Hz
Filter: Shelving type, 1st order

The midrange tone control shall have the following characteristics: 
fcenter = 775Hz
Filter: Peaking type, 2nd order, Q value calibratable with initial value of 1.1

The treble tone control shall have the following characteristics:
fcenter = 8kHz
Filter: Shelving type, 1st order

5.Source Offset
按照需求，对于不同的source，有不同的音量输出要求，在原来的音量上面进行一个dB值的调整