fixpoint_double_talk.c

电话通信中我们常会遇到回音,如何消除?本程序用自适应滤波器消除回音的方法来处理.(使用于音频信号处理)

// 
//  Project: Experiment 10.7.3 AEC using C55x Intrinsics - Chapter 10
//  File name: fixPoint_double_talk.c   
//
//  Description: This AEC uses the fixed-point leaky LMS algorithm
//
//  For the book "Real Time Digital Signal Processing: 
//                Implementation and Application, 2nd Ed"
//                By Sen M. Kuo, Bob H. Lee, and Wenshun Tian
//                Publisher: John Wiley and Sons, Ltd
//  Tools used:   CCS v.2.12.07
//                TMS320VC5510 DSK Rev-C
//

#include "fixPoint_leaky_lms.h"
#include "gsm.h"

void fixPoint_double_talk(DTALK *dtObj, LMS *lmsObj)
{ 
  long temp32a,temp32b;
  DTALK  *dt=(DTALK *)dtObj;
  LMS    *lms=(LMS *)lmsObj;

// Update far-end noise floor estimate of receiving far-end signal

  // temp = |farEndIn|, Estimate far end input power
  temp32a  = L_deposit_h(lms->in);
  // Estimate farEndIn power by short window
  dt->farInPowS = aec_power_estimate(dt->farInPowS,
                                     temp32a,ALPHA_SHIFT_SHORT);
  // Estimate farEndIn power by medium window
  dt->farInPowM = aec_power_estimate(dt->farInPowM,
                                     temp32a,ALPHA_SHIFT_MEDIUM);
                                     
  if (dt->nfFar < dt->farInPowS) 
  { // Onset of speech, slow update using long window
    dt->nfFar = aec_power_estimate(dt->nfFar,
                                   temp32a,ALPHA_SHIFT_MEDIUM);
  }              
  else 
  { // Offset of speech, fast decay using medium window
    dt->nfFar = aec_power_estimate(dt->nfFar,
                                   temp32a,ALPHA_SHIFT_SHORT);
  }              

  // Update near-end noise floor estimate of signal pickup by microphone 
  // temp = |microphoneIn|
  temp32a = L_deposit_h(lms->des);
  // Estimate microphone signal power by short window
  dt->micInPowS = aec_power_estimate(dt->micInPowS,
                                     temp32a,ALPHA_SHIFT_SHORT);
                                     
  if (dt->nfNear < dt->micInPowS) 
  { // Onset of speech, slow update using long window
    dt->nfNear = aec_power_estimate(dt->nfNear,
                                    temp32a,ALPHA_SHIFT_MEDIUM);
  }              
  else 
  { // Offset of speech, fast decay using medium window
    dt->nfNear = aec_power_estimate(dt->nfNear,
                                    temp32a,ALPHA_SHIFT_SHORT);
  }   

  // Error power  
  // Estimate power of AEC error by short window
  temp32a = L_deposit_h(lms->err);

  dt->errorAECpowS = aec_power_estimate(dt->errorAECpowS,
                                        temp32a,ALPHA_SHIFT_SHORT);
  // Estimate power of AEC error by medium window
  dt->errorAECpowM = aec_power_estimate(dt->errorAECpowM,
                                        temp32a,ALPHA_SHIFT_MEDIUM);

  // Threshold for far-end detector
  temp32b = dt->nfFar;   
  temp32b = L_add(temp32b,(SAFE_MARGIN>>1));                 

  // Threshold for near-end detector
  temp32a = dt->nfNear<<2;
  temp32a = L_add(temp32a,SAFE_MARGIN);

  if(temp32b <= (200<<15))
  {
    temp32b = (200<<15);
  }

  //  Detect speach activity at far end
  if(dt->farInPowS > temp32b)			// temp32b = thresFar
  { // Declare far-end speech 
    dt->farFlag = 1;					    
    // Set hangover time counter
    dt->farHangCount = HANGOVER_TIME; 
  }
  else
  {
    if (dt->farHangCount-- < 0)// Decrement hangover counter
    {
      dt->farFlag = 0;
      dt->farHangCount = 0;    // Hangover counter expired
    }
  }
                          
  if(temp32a <= (400<<15))
  {
    temp32a= (400<<15);
  }	
  if( (dt->micInPowS > temp32a) &&     // temp32a = thresNear
      (dt->errorAECpowS > temp32a) ) 
  {
    dt->nearFlag = 1;                  // Declare speech
    dt->nearHangCount = HANGOVER_TIME; // Set hangover counter
  }
  else
  {
    if (dt->nearHangCount-- < 0)       // Decrement hangover counter
    {
      dt->nearFlag = 0;
      dt->nearHangCount = 0;           // Hangover counter expired
    }
  }

  if(dt->trainTime-- <= 1 )
  {
    if(dt->nearFlag == 0 && dt->farFlag ==1)
    {
      lms->freez =0;
    }
    else 
    {
      lms->freez =1;
    }
		
    dt->trainTime =0;
  }
  else
  {
    lms->freez =0;
  }
}

/**************************************************************************
*  POWER_ESTIMATE - function to estimate power using a losy accumulator   *
***************************************************************************
*  Algorithm:
*    p(n) = p(n-1) + alpha * (abs(x(n) - p(n-1))
*
*************************************************************************/

long aec_power_estimate(long pn, long xn, short n)
{
  long p;

  p = L_abs(xn);
  p = L_sub(p,pn);
  p = L_shr_r(p,n);
  pn = L_add(pn,p);

  return(pn);
}