diff --git a/source/SoundTouch/FIRFilter.cpp b/source/SoundTouch/FIRFilter.cpp
index 5cc774f..54e2047 100644
--- a/source/SoundTouch/FIRFilter.cpp
+++ b/source/SoundTouch/FIRFilter.cpp
@@ -61,12 +61,15 @@ FIRFilter::FIRFilter()
     length = 0;
     lengthDiv8 = 0;
     filterCoeffs = NULL;
+    sum = NULL;
+    sumsize = 0;
 }
 
 
 FIRFilter::~FIRFilter()
 {
     delete[] filterCoeffs;
+    delete[] sum;
 }
 
 // Usual C-version of the filter routine for stereo sound
@@ -167,10 +170,18 @@ uint FIRFilter::evaluateFilterMono(SAMPLETYPE *dest, const SAMPLETYPE *src, uint
 }
 
 
-uint FIRFilter::evaluateFilterMulti(SAMPLETYPE *dest, const SAMPLETYPE *src, uint numSamples, uint numChannels) const
+uint FIRFilter::evaluateFilterMulti(SAMPLETYPE *dest, const SAMPLETYPE *src, uint numSamples, uint numChannels)
 {
     uint i, j, end, c;
-    LONG_SAMPLETYPE *sum=(LONG_SAMPLETYPE*)alloca(numChannels*sizeof(*sum));
+
+    if (sumsize < numChannels)
+    {
+        // allocate large enough array for keeping sums
+        sumsize = numChannels;
+        delete[] sum;
+        sum = new LONG_SAMPLETYPE[numChannels];
+    }
+
 #ifdef SOUNDTOUCH_FLOAT_SAMPLES
     // when using floating point samples, use a scaler instead of a divider
     // because division is much slower operation than multiplying.
@@ -253,7 +264,7 @@ uint FIRFilter::getLength() const
 //
 // Note : The amount of outputted samples is by value of 'filter_length' 
 // smaller than the amount of input samples.
-uint FIRFilter::evaluate(SAMPLETYPE *dest, const SAMPLETYPE *src, uint numSamples, uint numChannels) const
+uint FIRFilter::evaluate(SAMPLETYPE *dest, const SAMPLETYPE *src, uint numSamples, uint numChannels) 
 {
     assert(length > 0);
     assert(lengthDiv8 * 8 == length);
diff --git a/source/SoundTouch/FIRFilter.h b/source/SoundTouch/FIRFilter.h
index 622b9c4..6c213a6 100644
--- a/source/SoundTouch/FIRFilter.h
+++ b/source/SoundTouch/FIRFilter.h
@@ -65,13 +65,17 @@ protected:
     // Memory for filter coefficients
     SAMPLETYPE *filterCoeffs;
 
+    // Memory for keeping temporary sums in multichannel processing
+    LONG_SAMPLETYPE *sum;
+    uint sumsize;
+
     virtual uint evaluateFilterStereo(SAMPLETYPE *dest, 
                                       const SAMPLETYPE *src, 
                                       uint numSamples) const;
     virtual uint evaluateFilterMono(SAMPLETYPE *dest, 
                                     const SAMPLETYPE *src, 
                                     uint numSamples) const;
-    virtual uint evaluateFilterMulti(SAMPLETYPE *dest, const SAMPLETYPE *src, uint numSamples, uint numChannels) const;
+    virtual uint evaluateFilterMulti(SAMPLETYPE *dest, const SAMPLETYPE *src, uint numSamples, uint numChannels);
 
 public:
     FIRFilter();
@@ -91,7 +95,7 @@ public:
     uint evaluate(SAMPLETYPE *dest, 
                   const SAMPLETYPE *src, 
                   uint numSamples, 
-                  uint numChannels) const;
+                  uint numChannels);
 
     uint getLength() const;
 
diff --git a/source/SoundTouch/SoundTouch.cpp b/source/SoundTouch/SoundTouch.cpp
index ebca7ce..bbc46d7 100644
--- a/source/SoundTouch/SoundTouch.cpp
+++ b/source/SoundTouch/SoundTouch.cpp
@@ -348,8 +348,8 @@ void SoundTouch::flush()
     int i;
     int nUnprocessed;
     int nOut;
-    SAMPLETYPE *buff=(SAMPLETYPE*)alloca(64*channels*sizeof(SAMPLETYPE));
-
+    SAMPLETYPE *buff = new SAMPLETYPE[64 * channels];
+    
     // check how many samples still await processing, and scale
     // that by tempo & rate to get expected output sample count
     nUnprocessed = numUnprocessedSamples();
@@ -378,6 +378,8 @@ void SoundTouch::flush()
         }
     }
 
+    delete[] buff;
+
     // Clear working buffers
     pRateTransposer->clear();
     pTDStretch->clearInput();