diff --git a/services/audioflinger/AudioMixer.cpp b/services/audioflinger/AudioMixer.cpp
index 08325ad..529d1b5 100644
--- a/services/audioflinger/AudioMixer.cpp
+++ b/services/audioflinger/AudioMixer.cpp
@@ -98,7 +98,7 @@
 
 AudioMixer::AudioMixer(size_t frameCount, uint32_t sampleRate, uint32_t maxNumTracks)
     :   mTrackNames(0), mConfiguredNames((maxNumTracks >= 32 ? 0 : 1 << maxNumTracks) - 1),
-        mSampleRate(sampleRate)
+        mSampleRate(sampleRate), mLog(&mDummyLog)
 {
     // AudioMixer is not yet capable of multi-channel beyond stereo
     COMPILE_TIME_ASSERT_FUNCTION_SCOPE(2 == MAX_NUM_CHANNELS);
@@ -122,6 +122,7 @@
     mState.hook         = process__nop;
     mState.outputTemp   = NULL;
     mState.resampleTemp = NULL;
+    mState.mLog         = &mDummyLog;
     // mState.reserved
 
     // FIXME Most of the following initialization is probably redundant since
@@ -131,6 +132,7 @@
     for (unsigned i=0 ; i < MAX_NUM_TRACKS ; i++) {
         t->resampler = NULL;
         t->downmixerBufferProvider = NULL;
+        t->magic = track_t::kMagic;
         t++;
     }
 
@@ -169,6 +171,12 @@
     delete [] mState.resampleTemp;
 }
 
+void AudioMixer::setLog(NBLog::Writer *log)
+{
+    mLog = log;
+    mState.mLog = log;
+}
+
 int AudioMixer::getTrackName(audio_channel_mask_t channelMask, int sessionId)
 {
     uint32_t names = (~mTrackNames) & mConfiguredNames;
@@ -209,9 +217,12 @@
         t->mainBuffer = NULL;
         t->auxBuffer = NULL;
         t->downmixerBufferProvider = NULL;
+        t->fastIndex = -1;
+        // t->magic unchanged
 
         status_t status = initTrackDownmix(&mState.tracks[n], n, channelMask);
         if (status == OK) {
+            mLog->logf("getTrackName %d", n);
             return TRACK0 + n;
         }
         ALOGE("AudioMixer::getTrackName(0x%x) failed, error preparing track for downmix",
@@ -366,9 +377,11 @@
 {
     ALOGV("AudioMixer::deleteTrackName(%d)", name);
     name -= TRACK0;
+    mLog->logf("deleteTrackName %d", name);
     ALOG_ASSERT(uint32_t(name) < MAX_NUM_TRACKS, "bad track name %d", name);
     ALOGV("deleteTrackName(%d)", name);
     track_t& track(mState.tracks[ name ]);
+    track.checkMagic();
     if (track.enabled) {
         track.enabled = false;
         invalidateState(1<<name);
@@ -387,8 +400,10 @@
     name -= TRACK0;
     ALOG_ASSERT(uint32_t(name) < MAX_NUM_TRACKS, "bad track name %d", name);
     track_t& track = mState.tracks[name];
+    track.checkMagic();
 
     if (!track.enabled) {
+        mLog->logf("enable %d", name);
         track.enabled = true;
         ALOGV("enable(%d)", name);
         invalidateState(1 << name);
@@ -400,19 +415,32 @@
     name -= TRACK0;
     ALOG_ASSERT(uint32_t(name) < MAX_NUM_TRACKS, "bad track name %d", name);
     track_t& track = mState.tracks[name];
+    track.checkMagic();
 
     if (track.enabled) {
+        mLog->logf("disable %d", name);
         track.enabled = false;
         ALOGV("disable(%d)", name);
         invalidateState(1 << name);
     }
 }
 
+bool AudioMixer::enabled(int name)
+{
+    name -= TRACK0;
+    ALOG_ASSERT(uint32_t(name) < MAX_NUM_TRACKS, "bad track name %d", name);
+    track_t& track = mState.tracks[name];
+    track.checkMagic();
+
+    return track.enabled;
+}
+
 void AudioMixer::setParameter(int name, int target, int param, void *value)
 {
     name -= TRACK0;
     ALOG_ASSERT(uint32_t(name) < MAX_NUM_TRACKS, "bad track name %d", name);
     track_t& track = mState.tracks[name];
+    track.checkMagic();
 
     int valueInt = (int)value;
     int32_t *valueBuf = (int32_t *)value;
@@ -455,6 +483,9 @@
         //         for a specific track? or per mixer?
         /* case DOWNMIX_TYPE:
             break          */
+        case FAST_INDEX:
+            track.fastIndex = valueInt;
+            break;
         default:
             LOG_FATAL("bad param");
         }
@@ -540,6 +571,7 @@
 
 bool AudioMixer::track_t::setResampler(uint32_t value, uint32_t devSampleRate)
 {
+    checkMagic();
     if (value != devSampleRate || resampler != NULL) {
         if (sampleRate != value) {
             sampleRate = value;
@@ -572,6 +604,7 @@
 inline
 void AudioMixer::track_t::adjustVolumeRamp(bool aux)
 {
+    checkMagic();
     for (uint32_t i=0 ; i<MAX_NUM_CHANNELS ; i++) {
         if (((volumeInc[i]>0) && (((prevVolume[i]+volumeInc[i])>>16) >= volume[i])) ||
             ((volumeInc[i]<0) && (((prevVolume[i]+volumeInc[i])>>16) <= volume[i]))) {
@@ -600,8 +633,10 @@
 void AudioMixer::setBufferProvider(int name, AudioBufferProvider* bufferProvider)
 {
     name -= TRACK0;
+    mLog->logf("bp %d-%p", name, bufferProvider);
     ALOG_ASSERT(uint32_t(name) < MAX_NUM_TRACKS, "bad track name %d", name);
 
+    mState.tracks[name].checkMagic();
     if (mState.tracks[name].downmixerBufferProvider != NULL) {
         // update required?
         if (mState.tracks[name].downmixerBufferProvider->mTrackBufferProvider != bufferProvider) {
@@ -623,6 +658,9 @@
 
 void AudioMixer::process(int64_t pts)
 {
+    if (mState.needsChanged) {
+        mLog->logf("process needs=%#x", mState.needsChanged);
+    }
     mState.hook(&mState, pts);
 }
 
@@ -647,6 +685,7 @@
     }
     state->enabledTracks &= ~disabled;
     state->enabledTracks |=  enabled;
+    state->mLog->logf("process_validate ena=%#x", state->enabledTracks);
 
     // compute everything we need...
     int countActiveTracks = 0;
@@ -1103,6 +1142,7 @@
 
     // acquire each track's buffer
     uint32_t enabledTracks = state->enabledTracks;
+    state->mLog->logf("process_gNR ena=%#x", enabledTracks);
     uint32_t e0 = enabledTracks;
     while (e0) {
         const int i = 31 - __builtin_clz(e0);
@@ -1111,8 +1151,8 @@
         t.buffer.frameCount = state->frameCount;
         int valid = t.bufferProvider->getValid();
         if (valid != AudioBufferProvider::kValid) {
-            ALOGE("invalid bufferProvider=%p name=%d frameCount=%d valid=%#x enabledTracks=%#x",
-                    t.bufferProvider, i, t.buffer.frameCount, valid, enabledTracks);
+            ALOGE("invalid bufferProvider=%p name=%d fastIndex=%d frameCount=%d valid=%#x enabledTracks=%#x",
+                    t.bufferProvider, i, t.fastIndex, t.buffer.frameCount, valid, enabledTracks);
             // expect to crash
         }
         t.bufferProvider->getNextBuffer(&t.buffer, pts);