diff --git a/cwIoAudioMidiApp.cpp b/cwIoAudioMidiApp.cpp
index d299fea..46331bd 100644
--- a/cwIoAudioMidiApp.cpp
+++ b/cwIoAudioMidiApp.cpp
@@ -35,9 +35,11 @@ namespace cw
       kMidiThruCheckId,
       kCurMidiEvtCntId,
       kTotalMidiEvtCntId,
+      kMidiMuteCheckId,
       
       kCurAudioSecsId,
       kTotalAudioSecsId,
+      kAudioMuteCheckId,
                 
       kSaveBtnId,
       kOpenBtnId,
@@ -66,10 +68,11 @@ namespace cw
       { kPanelDivId,     kMidiThruCheckId,   "midiThruCheckId" },
       { kPanelDivId,     kCurMidiEvtCntId,   "curMidiEvtCntId" },      
       { kPanelDivId,     kTotalMidiEvtCntId, "totalMidiEvtCntId" },
+      { kPanelDivId,     kMidiMuteCheckId,   "midiMuteCheckId" },
       
       { kPanelDivId,     kCurAudioSecsId,    "curAudioSecsId" },
       { kPanelDivId,     kTotalAudioSecsId,  "totalAudioSecsId" },
-      
+      { kPanelDivId,     kAudioMuteCheckId,  "audioMuteCheckId" },
         
       { kPanelDivId,     kSaveBtnId,      "saveBtnId" },
       { kPanelDivId,     kOpenBtnId,      "openBtnId" },
@@ -388,6 +391,14 @@ namespace cw
           cwLogInfo("MIDI thru:%i",m.value->u.b);        
           _set_midi_thru_state(app, m.value->u.b);
           break;
+
+        case kMidiMuteCheckId:
+          midi_record_play::set_mute_state(app->mrpH,m.value->u.b);
+          break;
+
+        case kAudioMuteCheckId:
+          audio_record_play::set_mute_state(app->arpH,m.value->u.b);
+          break;
             
         case kStartBtnId:
           _on_ui_start(app);
diff --git a/cwIoAudioRecordPlay.cpp b/cwIoAudioRecordPlay.cpp
index b696d41..831ddb4 100644
--- a/cwIoAudioRecordPlay.cpp
+++ b/cwIoAudioRecordPlay.cpp
@@ -39,6 +39,8 @@ namespace cw
       unsigned       curFrameIdx;
       bool           recordFl;
       bool           startedFl;
+
+      bool           mute_fl;
       
       unsigned*      audioInChMapA;
       unsigned       audioInChMapN;
@@ -169,8 +171,11 @@ namespace cw
       for(unsigned chIdx=0; chIdx<chCnt; ++chIdx)
       {
         unsigned srcChIdx = p->audioInChMapA == nullptr ? chIdx : p->audioInChMapA[chIdx];
-        
-        memcpy(a->audioBuf + chIdx*asrc.dspFrameCnt, asrc.iBufArray[ srcChIdx ], asrc.dspFrameCnt * sizeof(sample_t));
+
+        if( srcChIdx >= asrc.iBufChCnt )
+          cwLogError(kInvalidArgRC,"Invalid input channel map index:%i >= %i.",srcChIdx,asrc.iBufChCnt);
+        else
+          memcpy(a->audioBuf + chIdx*asrc.dspFrameCnt, asrc.iBufArray[ srcChIdx ], asrc.dspFrameCnt * sizeof(sample_t));
       }
       
       a->chCnt        = chCnt;
@@ -197,31 +202,34 @@ namespace cw
     void _audio_play( audio_record_play_t* p, io::audio_msg_t& adst )
     {
       unsigned adst_idx = 0;
-      
-      while(adst_idx < adst.dspFrameCnt)
+
+      if( !p->mute_fl )
       {
-        am_audio_t* a;
-        unsigned sample_offs = 0;
-        if((a = _am_audio_from_sample_index(p, p->curFrameIdx, sample_offs )) == nullptr )
-          break;
-
-        unsigned n  = std::min(a->dspFrameCnt - sample_offs, adst.dspFrameCnt );
-
-
-        // TODO: Verify that this is correct - it looks like sample_offs should have to be incremented
-        
-        for(unsigned i=0; i<a->chCnt; ++i)
+        while(adst_idx < adst.dspFrameCnt)
         {
-          unsigned dstChIdx = p->audioOutChMapA != nullptr && i < p->audioOutChMapN ? p->audioOutChMapA[i] : i;
+          am_audio_t* a;
+          unsigned sample_offs = 0;
+          if((a = _am_audio_from_sample_index(p, p->curFrameIdx, sample_offs )) == nullptr )
+            break;
 
-          if( dstChIdx < adst.oBufChCnt )
-            memcpy( adst.oBufArray[ dstChIdx ] + adst_idx, a->audioBuf + sample_offs, n * sizeof(sample_t));
+          unsigned n  = std::min(a->dspFrameCnt - sample_offs, adst.dspFrameCnt );
+
+
+          // TODO: Verify that this is correct - it looks like sample_offs should have to be incremented
+        
+          for(unsigned i=0; i<a->chCnt; ++i)
+          {
+            unsigned dstChIdx = p->audioOutChMapA != nullptr && i < p->audioOutChMapN ? p->audioOutChMapA[i] : i;
+
+            if( dstChIdx < adst.oBufChCnt )
+              memcpy( adst.oBufArray[ dstChIdx ] + adst_idx, a->audioBuf + sample_offs, n * sizeof(sample_t));
+          }
+
+          p->curFrameIdx += n;
+          adst_idx       += n;
         }
-
-        p->curFrameIdx += n;
-        adst_idx       += n;
       }
-
+      
       // TODO: zero unused channels
 
       if( adst_idx < adst.dspFrameCnt )
@@ -415,9 +423,16 @@ namespace cw
         else
         {
           if( m.oBufChCnt > 0 )
+          {
             _audio_play(p,m);
+          }
         }
       }
+      else
+      {
+        for(unsigned i=0; i<m.oBufChCnt; ++i)
+          memset( m.oBufArray[i], 0, m.dspFrameCnt * sizeof(sample_t)); 
+      }
       
       return rc;
     }
@@ -522,6 +537,22 @@ bool cw::audio_record_play::record_state( handle_t h )
   return rc;
 }
 
+cw::rc_t cw::audio_record_play::set_mute_state( handle_t h, bool mute_fl )
+{
+  rc_t                 rc = kOkRC;
+  audio_record_play_t* p  = _handleToPtr(h);
+  p->mute_fl = true;
+  return rc;
+}
+
+bool cw::audio_record_play::mute_state( handle_t h )
+{
+  rc_t                 rc = kOkRC;
+  audio_record_play_t* p  = _handleToPtr(h);
+  return p->mute_fl;
+  return rc;
+}
+
 cw::rc_t cw::audio_record_play::save( handle_t h, const char* fn )
 {
   audio_record_play_t* p  = _handleToPtr(h);
diff --git a/cwIoAudioRecordPlay.h b/cwIoAudioRecordPlay.h
index 13273bb..c701b38 100644
--- a/cwIoAudioRecordPlay.h
+++ b/cwIoAudioRecordPlay.h
@@ -17,6 +17,8 @@ namespace cw
     rc_t clear( handle_t h );
     rc_t set_record_state( handle_t h, bool record_fl );
     bool record_state( handle_t h );
+    rc_t set_mute_state( handle_t h, bool mute_fl );
+    bool mute_state( handle_t h );
     rc_t save( handle_t h, const char* fn );
     rc_t open( handle_t h, const char* fn );
     double duration_seconds( handle_t h );
diff --git a/cwIoMidiRecordPlay.h b/cwIoMidiRecordPlay.h
index d785384..400bb66 100644
--- a/cwIoMidiRecordPlay.h
+++ b/cwIoMidiRecordPlay.h
@@ -41,6 +41,9 @@ namespace cw
     rc_t set_record_state( handle_t h, bool record_fl );
     bool record_state( handle_t h );
 
+    rc_t set_mute_state( handle_t h, bool record_fl );
+    bool mute_state( handle_t h );
+
     rc_t set_thru_state( handle_t h, bool record_thru );
     bool thru_state( handle_t h );