echocancel.c

一个滤波器和一个音效处理程序 TI 的CCS 编译器编程。

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/***********************************************************************
**  File Name:    EchoCancel.c
**  Part Number:  TLV320AIC10/11EVM-SW-00004
************************************************************************
**  Copyright (c) Texas Instruments, Inc. 2000
************************************************************************
**
**  Release History:
**     Version      Date          Engr          Description
**      1.00     10-11-2000    Wendy X Fang   Original Release
**
************************************************************************
**
**  Function: 
**      This routine will run at KHz through main routine, that cancels
**      the echo from near end speaker to microphone.
**
**    far end microphone SIn(n)  --------> near end speaker Tonewave(n)
**                                    |
**                                    h(z)
**                                    |
**                              e^(n) |+  
**   far end speaker SOut(n) <--------+---- near end mic SL_ADC 
**                             r(n)     - e(n) 
**
**  (The following code need further testing -WXF).
***********************************************************************/
/***********************************************************************
** Include Statements
***********************************************************************/
#include   "EchoCancel.h"

/***********************************************************************
**  Function Routine
***********************************************************************/
void  EchoCancel(void)
{
      /******* FIR Filter Output: 
        e^(n) = h(0)*SIn(0)+h(1)*SIn(1)+...+h(N-1)*SIn(N-1)
      *******/
     EchoEst = 0;
     NCount  = 0;
     while (NCount < FilterLength)
     {
         EchoEst += h[NCount]*SIn[NCount];
         NCount++;
     }

      /******* Compute Echo Residual:
         r(n) =  e(n) - e^(n)
         where: e(n), Echo from Near End microphone
                X(n)+e(n) = SL_ADC = e(n) if X(n)=0
      *******/
         EchoResid = SL_ADC - (EchoEst >> 16);  
  
      /******* Get Far-End Input Power:
         P = P*(N-1)/N + SIn^2/N
      ********/
      PowerSIn =  ((PowerSIn*(FilterLength-1)) >> Alpha) + 
                  ((SIn[0]*SIn[0]) >> Alpha);

      /******* Update Adaptive Filter Parameter
      h(n) = h(n-1) + mu*r(n)*SIn(n)/P
      *******/
      NCount = FilterLength - 1;
      while (NCount > 0)
      {
          h[NCount]  += Mu*EchoResid*SIn[NCount]/PowerSIn;
          SIn[NCount] = SIn[NCount-1];
          NCount--;
      }
      h[0]  += Mu*EchoResid*SIn[0]/PowerSIn;
      SIn[0] = ToneWave;  
      
      /****** Output to Master Speaker
      SOut = EchoResid/2
      *******/
      SOut = (EchoResid >> 1 );   /* scaled output to far end speaker */
      SOut &= 0xFFFE;

}

/***********************************************************************
**  End of File -- EchoCancel.c
***********************************************************************/