diff --git a/src/AudioIO.cpp b/src/AudioIO.cpp
index fc904d138..996269d00 100644
--- a/src/AudioIO.cpp
+++ b/src/AudioIO.cpp
@@ -2102,7 +2102,7 @@ bool AudioIoCallback::FillOutputBuffers(
          // Do realtime effects
          if( !dropQuickly && len > 0 ) {
             if (pScope)
-               pScope->Process(mTrackChannelsBuffer[0], mAudioScratchBuffers.data(), len);
+               pScope->Process(mTrackChannelsBuffer[0], mAudioScratchBuffers.data(), mScratchPointers.data(), len);
             // Mix the results with the existing output (software playthrough) and
             // apply panning.  If post panning effects are desired, the panning would
             // need to be be split out from the mixing and applied in a separate step.
diff --git a/src/effects/RealtimeEffectManager.cpp b/src/effects/RealtimeEffectManager.cpp
index 23ca98863..c785128b9 100644
--- a/src/effects/RealtimeEffectManager.cpp
+++ b/src/effects/RealtimeEffectManager.cpp
@@ -173,8 +173,8 @@ void RealtimeEffectManager::ProcessStart()
 // This will be called in a different thread than the main GUI thread.
 //
 size_t RealtimeEffectManager::Process(Track *track,
-                                      float **buffers,
-                                      size_t numSamples)
+   float *const *buffers, float *const *scratch,
+   size_t numSamples)
 {
    using namespace std::chrono;
 
@@ -197,15 +197,13 @@ size_t RealtimeEffectManager::Process(Track *track,
       static_cast<float **>(alloca(chans * sizeof(float *)));
    const auto obuf =
       static_cast<float **>(alloca(chans * sizeof(float *)));
-   const auto scratch =
-      static_cast<float*>(alloca(numSamples * sizeof(float)));
 
    // And populate the input with the buffers we've been given while allocating
    // NEW output buffers
    for (unsigned int i = 0; i < chans; i++)
    {
       ibuf[i] = buffers[i];
-      obuf[i] = static_cast<float*>(alloca(numSamples * sizeof(float)));
+      obuf[i] = scratch[i];
    }
 
    // Now call each effect in the chain while swapping buffer pointers to feed the
@@ -218,8 +216,7 @@ size_t RealtimeEffectManager::Process(Track *track,
          if (bypassed)
             return;
 
-         state.Process(track, chans, ibuf, obuf, scratch, numSamples);
-
+         state.Process(track, chans, ibuf, obuf, scratch[chans], numSamples);
          for (auto i = 0; i < chans; ++i)
             std::swap(ibuf[i], obuf[i]);
          called++;
diff --git a/src/effects/RealtimeEffectManager.h b/src/effects/RealtimeEffectManager.h
index 6d679f409..aa81bd86c 100644
--- a/src/effects/RealtimeEffectManager.h
+++ b/src/effects/RealtimeEffectManager.h
@@ -86,7 +86,9 @@ class TENACITY_DLL_API RealtimeEffectManager final
 
    friend RealtimeEffects::ProcessingScope;
    void ProcessStart();
-   size_t Process(Track *track, float **buffers, size_t numSamples);
+   /*! @copydoc ProcessScope::Process */
+   size_t Process(Track *track,
+      float *const *buffers, float *const *scratch, size_t numSamples);
    void ProcessEnd() noexcept;
 
    RealtimeEffectManager(const RealtimeEffectManager&) = delete;
@@ -196,11 +198,17 @@ class ProcessingScope {
          RealtimeEffectManager::Get(*pProject).ProcessEnd();
    }
 
-   size_t Process(Track *track, float **buffers, size_t numSamples)
+   size_t Process(Track *track,
+      float *const *buffers, /*!< Assume as many buffers, as channels were
+         specified in the AddTrack call */
+      float *const *scratch, /*!< As many temporary buffers as in buffers,
+         plus one more */
+      size_t numSamples //!< length of each buffer
+   )
    {
       if (auto pProject = mwProject.lock())
          return RealtimeEffectManager::Get(*pProject)
-            .Process(track, buffers, numSamples);
+            .Process(track, buffers, scratch, numSamples);
       else
          return numSamples; // consider them trivially processed
    }