Using buffered signal to calculate the level of echo cancellation.

webrtc/modules/audio_processing/aec/aec_core.c

Index: webrtc/modules/audio_processing/aec/aec_core.c
diff --git a/webrtc/modules/audio_processing/aec/aec_core.c b/webrtc/modules/audio_processing/aec/aec_core.c
index 26e13bc2c2dac54529e129c62ab964e3befd282d..112758c4cde7deaf543a0f00e0b827650d038f2e 100644
--- a/webrtc/modules/audio_processing/aec/aec_core.c
+++ b/webrtc/modules/audio_processing/aec/aec_core.c
@@ -667,12 +667,11 @@ static void UpdateMetrics(AecCore* aec) {
 
       // A_NLP
       dtmp = 10 * (float)log10(aec->nearlevel.averagelevel /
-                                   (2 * aec->linoutlevel.averagelevel) +
-                               1e-10f);
+          aec->linoutlevel.averagelevel + 1e-10f);
 
       // subtract noise power
-      suppressedEcho = 2 * (aec->linoutlevel.averagelevel -
-                            safety * aec->linoutlevel.minlevel);
+      suppressedEcho = aec->linoutlevel.averagelevel -
+          safety * aec->linoutlevel.minlevel;
 
       dtmp2 = 10 * (float)log10(echo / suppressedEcho + 1e-10f);
 
@@ -903,7 +902,6 @@ static void EchoSubtraction(
     AecCore* aec,
     int num_partitions,
     int x_fft_buf_block_pos,
-    int metrics_mode,
     int extended_filter_enabled,
     float normal_mu,
     float normal_error_threshold,
@@ -911,7 +909,6 @@ static void EchoSubtraction(
     float* const y,
     float x_pow[PART_LEN1],
     float h_fft_buf[2][kExtendedNumPartitions * PART_LEN1],
-    PowerLevel* linout_level,
     float echo_subtractor_output[PART_LEN]) {
   float s_fft[2][PART_LEN1];
   float e_extended[PART_LEN2];
@@ -955,13 +952,6 @@ static void EchoSubtraction(
                           &e_fft[0][0],
                           sizeof(e_fft[0][0]) * PART_LEN1 * 2);
 
-  if (metrics_mode == 1) {
-    // Note that the first PART_LEN samples in fft (before transformation) are
-    // zero. Hence, the scaling by two in UpdateLevel() should not be
-    // performed. That scaling is taken care of in UpdateMetrics() instead.
-    UpdateLevel(linout_level, CalculatePower(e, PART_LEN) / 2.0f);
-  }
-
   // Scale error signal inversely with far power.
   WebRtcAec_ScaleErrorSignal(extended_filter_enabled,
                              normal_mu,
@@ -976,7 +966,6 @@ static void EchoSubtraction(
   memcpy(echo_subtractor_output, e, sizeof(float) * PART_LEN);
 }
 
-
 static void EchoSuppression(AecCore* aec,
                             float farend[PART_LEN2],
                             float* echo_subtractor_output,
@@ -1010,11 +999,6 @@ static void EchoSuppression(AecCore* aec,
 
   float* xfw_ptr = NULL;
 
-  // Update eBuf with echo subtractor output.
-  memcpy(aec->eBuf + PART_LEN,
-         echo_subtractor_output,
-         sizeof(float) * PART_LEN);
-
   // Analysis filter banks for the echo suppressor.
   // Windowed near-end ffts.
   WindowData(fft, aec->dBuf);
@@ -1374,7 +1358,6 @@ static void ProcessBlock(AecCore* aec) {
   EchoSubtraction(aec,
                   aec->num_partitions,
                   aec->xfBufBlockPos,
-                  aec->metricsMode,
                   aec->extended_filter_enabled,
                   aec->normal_mu,
                   aec->normal_error_threshold,
@@ -1382,11 +1365,19 @@ static void ProcessBlock(AecCore* aec) {
                   nearend_ptr,
                   aec->xPow,
                   aec->wfBuf,
-                  &aec->linoutlevel,
                   echo_subtractor_output);
 
   RTC_AEC_DEBUG_WAV_WRITE(aec->outLinearFile, echo_subtractor_output, PART_LEN);
 
+  // Update eBuf with echo subtractor output.

[peah-webrtc, 2016/01/25 12:23:02]

This may be affected by changes in the future. As it is now, linoutLevel is
always the level of the linear filter output. Currently, that is equivalent to
echo_subtractor_output but that will change. For instance, during filter
divergence, echo_subtractor_output should be equal to the microphone signal
rather than the linear filter output.

That change may be fine though, depending upon how the metric should be used. If
it is a metric over the ERLE achieved by the EchoSubtraction function call, that
is fine, but if it is a metric of the ERLE currently achieved by the adaptive
filter, that will in that case no longer be correct.

 Just wanted to give a hea

[minyue-webrtc, 2016/01/25 14:26:55]

Good point. It is true that when the linear filter diverges, we bypass it and
the performance of the linear filter does not correspond to any echo
cancellation performance. However, the divergence status can still be used since
1. it works as a double-talk detector
2. it should not toggle too often

Regarding ERLE, this change does not affect it. It affects only A_NLP.

+  memcpy(aec->eBuf + PART_LEN,
+         echo_subtractor_output,
+         sizeof(float) * PART_LEN);
+
+  if (aec->metricsMode == 1) {
+    UpdateLevel(&aec->linoutlevel, CalculatePower(aec->eBuf, PART_LEN2));
+  }
+
   // Perform echo suppression.
   EchoSuppression(aec, farend_ptr, echo_subtractor_output, output, outputH_ptr);