diff --git a/include/boo/audiodev/IAudioVoice.hpp b/include/boo/audiodev/IAudioVoice.hpp
index ded59b8..f0e5b5e 100644
--- a/include/boo/audiodev/IAudioVoice.hpp
+++ b/include/boo/audiodev/IAudioVoice.hpp
@@ -63,10 +63,10 @@ struct IAudioVoice
     virtual void setDefaultMatrixCoefficients()=0;
 
     /** Set channel-gains for mono audio source (AudioChannel enum for array index) */
-    virtual void setMonoMatrixCoefficients(const float coefs[8])=0;
+    virtual void setMonoMatrixCoefficients(const float coefs[8], bool slew)=0;
 
     /** Set channel-gains for stereo audio source (AudioChannel enum for array index) */
-    virtual void setStereoMatrixCoefficients(const float coefs[8][2])=0;
+    virtual void setStereoMatrixCoefficients(const float coefs[8][2], bool slew)=0;
 
     /** Called by client to dynamically adjust the pitch of voices with dynamic pitch enabled */
     virtual void setPitchRatio(double ratio, bool slew)=0;
diff --git a/lib/audiodev/AudioMatrix.cpp b/lib/audiodev/AudioMatrix.cpp
index 995ae49..e5a1598 100644
--- a/lib/audiodev/AudioMatrix.cpp
+++ b/lib/audiodev/AudioMatrix.cpp
@@ -7,6 +7,8 @@ namespace boo
 
 void AudioMatrixMono::setDefaultMatrixCoefficients(AudioChannelSet acSet)
 {
+    m_curSlewFrame = 0;
+    m_slewFrames = 0;
     memset(m_coefs, 0, sizeof(m_coefs));
     switch (acSet)
     {
@@ -24,58 +26,126 @@ void AudioMatrixMono::setDefaultMatrixCoefficients(AudioChannelSet acSet)
 }
 
 int16_t* AudioMatrixMono::mixMonoSampleData(const AudioVoiceEngineMixInfo& info,
-                                            const int16_t* dataIn, int16_t* dataOut, size_t samples) const
+                                            const int16_t* dataIn, int16_t* dataOut, size_t samples)
 {
     const ChannelMap& chmap = info.m_channelMap;
     for (size_t s=0 ; s<samples ; ++s, ++dataIn)
-        for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+    {
+        if (m_slewFrames && m_curSlewFrame < m_slewFrames)
         {
-            AudioChannel ch = chmap.m_channels[c];
-            if (ch != AudioChannel::Unknown)
+            double t = m_curSlewFrame / double(m_slewFrames);
+            double omt = 1.0 - t;
+
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
             {
-                *dataOut = Clamp16(*dataOut + *dataIn * m_coefs[int(ch)]);
-                ++dataOut;
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp16(*dataOut + *dataIn * (m_coefs[int(ch)] * t + m_oldCoefs[int(ch)] * omt));
+                    ++dataOut;
+                }
+            }
+
+            ++m_curSlewFrame;
+        }
+        else
+        {
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+            {
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp16(*dataOut + *dataIn * m_coefs[int(ch)]);
+                    ++dataOut;
+                }
             }
         }
+    }
     return dataOut;
 }
 
 int32_t* AudioMatrixMono::mixMonoSampleData(const AudioVoiceEngineMixInfo& info,
-                                            const int32_t* dataIn, int32_t* dataOut, size_t samples) const
+                                            const int32_t* dataIn, int32_t* dataOut, size_t samples)
 {
     const ChannelMap& chmap = info.m_channelMap;
     for (size_t s=0 ; s<samples ; ++s, ++dataIn)
-        for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+    {
+        if (m_slewFrames && m_curSlewFrame < m_slewFrames)
         {
-            AudioChannel ch = chmap.m_channels[c];
-            if (ch != AudioChannel::Unknown)
+            double t = m_curSlewFrame / double(m_slewFrames);
+            double omt = 1.0 - t;
+
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
             {
-                *dataOut = Clamp32(*dataOut + *dataIn * m_coefs[int(ch)]);
-                ++dataOut;
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp32(*dataOut + *dataIn * (m_coefs[int(ch)] * t + m_oldCoefs[int(ch)] * omt));
+                    ++dataOut;
+                }
+            }
+
+            ++m_curSlewFrame;
+        }
+        else
+        {
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+            {
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp32(*dataOut + *dataIn * m_coefs[int(ch)]);
+                    ++dataOut;
+                }
             }
         }
+    }
     return dataOut;
 }
 
 float* AudioMatrixMono::mixMonoSampleData(const AudioVoiceEngineMixInfo& info,
-                                          const float* dataIn, float* dataOut, size_t samples) const
+                                          const float* dataIn, float* dataOut, size_t samples)
 {
     const ChannelMap& chmap = info.m_channelMap;
     for (size_t s=0 ; s<samples ; ++s, ++dataIn)
-        for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+    {
+        if (m_slewFrames && m_curSlewFrame < m_slewFrames)
         {
-            AudioChannel ch = chmap.m_channels[c];
-            if (ch != AudioChannel::Unknown)
+            double t = m_curSlewFrame / double(m_slewFrames);
+            double omt = 1.0 - t;
+
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
             {
-                *dataOut = ClampFlt(*dataOut + *dataIn * m_coefs[int(ch)]);
-                ++dataOut;
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = ClampFlt(*dataOut + *dataIn * (m_coefs[int(ch)] * t + m_oldCoefs[int(ch)] * omt));
+                    ++dataOut;
+                }
+            }
+
+            ++m_curSlewFrame;
+        }
+        else
+        {
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+            {
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = ClampFlt(*dataOut + *dataIn * m_coefs[int(ch)]);
+                    ++dataOut;
+                }
             }
         }
+    }
     return dataOut;
 }
 
 void AudioMatrixStereo::setDefaultMatrixCoefficients(AudioChannelSet acSet)
 {
+    m_curSlewFrame = 0;
+    m_slewFrames = 0;
     memset(m_coefs, 0, sizeof(m_coefs));
     switch (acSet)
     {
@@ -94,59 +164,131 @@ void AudioMatrixStereo::setDefaultMatrixCoefficients(AudioChannelSet acSet)
 }
 
 int16_t* AudioMatrixStereo::mixStereoSampleData(const AudioVoiceEngineMixInfo& info,
-                                                const int16_t* dataIn, int16_t* dataOut, size_t frames) const
+                                                const int16_t* dataIn, int16_t* dataOut, size_t frames)
 {
     const ChannelMap& chmap = info.m_channelMap;
     for (size_t f=0 ; f<frames ; ++f, dataIn += 2)
-        for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+    {
+        if (m_slewFrames && m_curSlewFrame < m_slewFrames)
         {
-            AudioChannel ch = chmap.m_channels[c];
-            if (ch != AudioChannel::Unknown)
+            double t = m_curSlewFrame / double(m_slewFrames);
+            double omt = 1.0 - t;
+
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
             {
-                *dataOut = Clamp16(*dataOut +
-                                   dataIn[0] * m_coefs[int(ch)][0] +
-                                   dataIn[1] * m_coefs[int(ch)][1]);
-                ++dataOut;
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp16(*dataOut +
+                                       *dataIn * (m_coefs[int(ch)][0] * t + m_oldCoefs[int(ch)][0] * omt) +
+                                       *dataIn * (m_coefs[int(ch)][1] * t + m_oldCoefs[int(ch)][1] * omt));
+                    ++dataOut;
+                }
+            }
+
+            ++m_curSlewFrame;
+        }
+        else
+        {
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+            {
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp16(*dataOut +
+                                       dataIn[0] * m_coefs[int(ch)][0] +
+                                       dataIn[1] * m_coefs[int(ch)][1]);
+                    ++dataOut;
+                }
             }
         }
+    }
     return dataOut;
 }
 
 int32_t* AudioMatrixStereo::mixStereoSampleData(const AudioVoiceEngineMixInfo& info,
-                                                const int32_t* dataIn, int32_t* dataOut, size_t frames) const
+                                                const int32_t* dataIn, int32_t* dataOut, size_t frames)
 {
     const ChannelMap& chmap = info.m_channelMap;
     for (size_t f=0 ; f<frames ; ++f, dataIn += 2)
-        for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+    {
+        if (m_slewFrames && m_curSlewFrame < m_slewFrames)
         {
-            AudioChannel ch = chmap.m_channels[c];
-            if (ch != AudioChannel::Unknown)
+            double t = m_curSlewFrame / double(m_slewFrames);
+            double omt = 1.0 - t;
+
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
             {
-                *dataOut = Clamp32(*dataOut +
-                                   dataIn[0] * m_coefs[int(ch)][0] +
-                                   dataIn[1] * m_coefs[int(ch)][1]);
-                ++dataOut;
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp32(*dataOut +
+                                       *dataIn * (m_coefs[int(ch)][0] * t + m_oldCoefs[int(ch)][0] * omt) +
+                                       *dataIn * (m_coefs[int(ch)][1] * t + m_oldCoefs[int(ch)][1] * omt));
+                    ++dataOut;
+                }
+            }
+
+            ++m_curSlewFrame;
+        }
+        else
+        {
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+            {
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = Clamp32(*dataOut +
+                                       dataIn[0] * m_coefs[int(ch)][0] +
+                                       dataIn[1] * m_coefs[int(ch)][1]);
+                    ++dataOut;
+                }
             }
         }
+    }
     return dataOut;
 }
 
 float* AudioMatrixStereo::mixStereoSampleData(const AudioVoiceEngineMixInfo& info,
-                                              const float* dataIn, float* dataOut, size_t frames) const
+                                              const float* dataIn, float* dataOut, size_t frames)
 {
     const ChannelMap& chmap = info.m_channelMap;
     for (size_t f=0 ; f<frames ; ++f, dataIn += 2)
-        for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+    {
+        if (m_slewFrames && m_curSlewFrame < m_slewFrames)
         {
-            AudioChannel ch = chmap.m_channels[c];
-            if (ch != AudioChannel::Unknown)
+            double t = m_curSlewFrame / double(m_slewFrames);
+            double omt = 1.0 - t;
+
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
             {
-                *dataOut = ClampFlt(*dataOut +
-                                    dataIn[0] * m_coefs[int(ch)][0] +
-                                    dataIn[1] * m_coefs[int(ch)][1]);
-                ++dataOut;
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = ClampFlt(*dataOut +
+                                        *dataIn * (m_coefs[int(ch)][0] * t + m_oldCoefs[int(ch)][0] * omt) +
+                                        *dataIn * (m_coefs[int(ch)][1] * t + m_oldCoefs[int(ch)][1] * omt));
+                    ++dataOut;
+                }
+            }
+
+            ++m_curSlewFrame;
+        }
+        else
+        {
+            for (unsigned c=0 ; c<chmap.m_channelCount ; ++c)
+            {
+                AudioChannel ch = chmap.m_channels[c];
+                if (ch != AudioChannel::Unknown)
+                {
+                    *dataOut = ClampFlt(*dataOut +
+                                        dataIn[0] * m_coefs[int(ch)][0] +
+                                        dataIn[1] * m_coefs[int(ch)][1]);
+                    ++dataOut;
+                }
             }
         }
+    }
     return dataOut;
 }
 
diff --git a/lib/audiodev/AudioMatrix.hpp b/lib/audiodev/AudioMatrix.hpp
index 25f33d5..a057dc2 100644
--- a/lib/audiodev/AudioMatrix.hpp
+++ b/lib/audiodev/AudioMatrix.hpp
@@ -39,47 +39,66 @@ static inline float ClampFlt(float in)
 
 class AudioMatrixMono
 {
-    float m_coefs[8];
+    float m_coefs[8] = {};
+    float m_oldCoefs[8] = {};
+    size_t m_slewFrames = 0;
+    size_t m_curSlewFrame = 0;
 public:
     AudioMatrixMono() {setDefaultMatrixCoefficients(AudioChannelSet::Stereo);}
 
     void setDefaultMatrixCoefficients(AudioChannelSet acSet);
-    void setMatrixCoefficients(const float coefs[8])
+    void setMatrixCoefficients(const float coefs[8], size_t slewFrames=0)
     {
+        m_slewFrames = slewFrames;
+        m_curSlewFrame = 0;
         for (int i=0 ; i<8 ; ++i)
+        {
+            if (m_curSlewFrame == m_slewFrames)
+                m_oldCoefs[i] = m_coefs[i];
             m_coefs[i] = coefs[i];
+        }
     }
 
     int16_t* mixMonoSampleData(const AudioVoiceEngineMixInfo& info,
-                               const int16_t* dataIn, int16_t* dataOut, size_t samples) const;
+                               const int16_t* dataIn, int16_t* dataOut, size_t samples);
     int32_t* mixMonoSampleData(const AudioVoiceEngineMixInfo& info,
-                               const int32_t* dataIn, int32_t* dataOut, size_t samples) const;
+                               const int32_t* dataIn, int32_t* dataOut, size_t samples);
     float* mixMonoSampleData(const AudioVoiceEngineMixInfo& info,
-                             const float* dataIn, float* dataOut, size_t samples) const;
+                             const float* dataIn, float* dataOut, size_t samples);
 };
 
 class AudioMatrixStereo
 {
-    float m_coefs[8][2];
+    float m_coefs[8][2] = {};
+    float m_oldCoefs[8][2] = {};
+    size_t m_slewFrames = 0;
+    size_t m_curSlewFrame = 0;
 public:
     AudioMatrixStereo() {setDefaultMatrixCoefficients(AudioChannelSet::Stereo);}
 
     void setDefaultMatrixCoefficients(AudioChannelSet acSet);
-    void setMatrixCoefficients(const float coefs[8][2])
+    void setMatrixCoefficients(const float coefs[8][2], size_t slewFrames=0)
     {
+        m_slewFrames = slewFrames;
+        m_curSlewFrame = 0;
         for (int i=0 ; i<8 ; ++i)
         {
+            if (m_curSlewFrame == m_slewFrames)
+            {
+                m_oldCoefs[i][0] = m_coefs[i][0];
+                m_oldCoefs[i][1] = m_coefs[i][1];
+            }
             m_coefs[i][0] = coefs[i][0];
             m_coefs[i][1] = coefs[i][1];
         }
     }
 
     int16_t* mixStereoSampleData(const AudioVoiceEngineMixInfo& info,
-                                 const int16_t* dataIn, int16_t* dataOut, size_t frames) const;
+                                 const int16_t* dataIn, int16_t* dataOut, size_t frames);
     int32_t* mixStereoSampleData(const AudioVoiceEngineMixInfo& info,
-                                 const int32_t* dataIn, int32_t* dataOut, size_t frames) const;
+                                 const int32_t* dataIn, int32_t* dataOut, size_t frames);
     float* mixStereoSampleData(const AudioVoiceEngineMixInfo& info,
-                               const float* dataIn, float* dataOut, size_t frames) const;
+                               const float* dataIn, float* dataOut, size_t frames);
 };
 
 }
diff --git a/lib/audiodev/AudioVoice.cpp b/lib/audiodev/AudioVoice.cpp
index 9cc3311..0cde7f3 100644
--- a/lib/audiodev/AudioVoice.cpp
+++ b/lib/audiodev/AudioVoice.cpp
@@ -166,12 +166,12 @@ void AudioVoiceMono::setDefaultMatrixCoefficients()
     m_matrix.setDefaultMatrixCoefficients(m_parent.mixInfo().m_channels);
 }
 
-void AudioVoiceMono::setMonoMatrixCoefficients(const float coefs[8])
+void AudioVoiceMono::setMonoMatrixCoefficients(const float coefs[8], bool slew)
 {
-    m_matrix.setMatrixCoefficients(coefs);
+    m_matrix.setMatrixCoefficients(coefs, slew ? m_root.m_5msFrames : 0);
 }
 
-void AudioVoiceMono::setStereoMatrixCoefficients(const float coefs[8][2])
+void AudioVoiceMono::setStereoMatrixCoefficients(const float coefs[8][2], bool slew)
 {
     float newCoefs[8] =
     {
@@ -184,7 +184,7 @@ void AudioVoiceMono::setStereoMatrixCoefficients(const float coefs[8][2])
         coefs[6][0],
         coefs[7][0]
     };
-    m_matrix.setMatrixCoefficients(newCoefs);
+    m_matrix.setMatrixCoefficients(newCoefs, slew ? m_root.m_5msFrames : 0);
 }
 
 AudioVoiceStereo::AudioVoiceStereo(BaseAudioVoiceEngine& root, IAudioMix& parent, IAudioVoiceCallback* cb,
@@ -286,7 +286,7 @@ void AudioVoiceStereo::setDefaultMatrixCoefficients()
     m_matrix.setDefaultMatrixCoefficients(m_parent.mixInfo().m_channels);
 }
 
-void AudioVoiceStereo::setMonoMatrixCoefficients(const float coefs[8])
+void AudioVoiceStereo::setMonoMatrixCoefficients(const float coefs[8], bool slew)
 {
     float newCoefs[8][2] =
     {
@@ -299,12 +299,12 @@ void AudioVoiceStereo::setMonoMatrixCoefficients(const float coefs[8])
         {coefs[6], coefs[6]},
         {coefs[7], coefs[7]}
     };
-    m_matrix.setMatrixCoefficients(newCoefs);
+    m_matrix.setMatrixCoefficients(newCoefs, slew ? m_root.m_5msFrames : 0);
 }
 
-void AudioVoiceStereo::setStereoMatrixCoefficients(const float coefs[8][2])
+void AudioVoiceStereo::setStereoMatrixCoefficients(const float coefs[8][2], bool slew)
 {
-    m_matrix.setMatrixCoefficients(coefs);
+    m_matrix.setMatrixCoefficients(coefs, slew ? m_root.m_5msFrames : 0);
 }
 
 }
diff --git a/lib/audiodev/AudioVoice.hpp b/lib/audiodev/AudioVoice.hpp
index 5e62cb6..c9491b9 100644
--- a/lib/audiodev/AudioVoice.hpp
+++ b/lib/audiodev/AudioVoice.hpp
@@ -85,8 +85,8 @@ public:
     AudioVoiceMono(BaseAudioVoiceEngine& root, IAudioMix& parent, IAudioVoiceCallback* cb,
                    double sampleRate, bool dynamicRate);
     void setDefaultMatrixCoefficients();
-    void setMonoMatrixCoefficients(const float coefs[8]);
-    void setStereoMatrixCoefficients(const float coefs[8][2]);
+    void setMonoMatrixCoefficients(const float coefs[8], bool slew);
+    void setStereoMatrixCoefficients(const float coefs[8][2], bool slew);
 };
 
 class AudioVoiceStereo : public AudioVoice
@@ -105,8 +105,8 @@ public:
     AudioVoiceStereo(BaseAudioVoiceEngine& root, IAudioMix& parent, IAudioVoiceCallback* cb,
                      double sampleRate, bool dynamicRate);
     void setDefaultMatrixCoefficients();
-    void setMonoMatrixCoefficients(const float coefs[8]);
-    void setStereoMatrixCoefficients(const float coefs[8][2]);
+    void setMonoMatrixCoefficients(const float coefs[8], bool slew);
+    void setStereoMatrixCoefficients(const float coefs[8][2], bool slew);
 };
 
 }