diff --git a/src/sfizz/AtomicGuard.h b/src/sfizz/AtomicGuard.h
deleted file mode 100644
index 16d1f4dd..00000000
--- a/src/sfizz/AtomicGuard.h
+++ /dev/null
@@ -1,114 +0,0 @@
-// SPDX-License-Identifier: BSD-2-Clause
-
-// This code is part of the sfizz library and is licensed under a BSD 2-clause
-// license. You should have receive a LICENSE.md file along with the code.
-// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
-
-/**
- * @brief This file contains a pair of RAII helpers that handle some form
- * of lock-free mutex-type protection adapter to audio applications where you have 1 priority thread
- * that should never block and would rather return silence than wait, and another low-priority
- * thread that handles long computations.
- *
- * @code{.cpp}
- *
- * // Somewhere in a class...
- * std::atomic<bool> canEnterCallback;
- * std::atomic<bool> inCallback;
- *
- * void functionThatSuspendsCallback()
- * {
- *     AtomicDisabler callbackDisabler { canEnterCallback };
- *
- *     while (inCallback) {
- *         std::this_thread::sleep_for(1ms);
- *     }
- *
- * 	   // Do your thing.
- * }
- *
- * void callback(int samplesPerBlock) noexcept
- * {
- *     AtomicGuard callbackGuard { inCallback };
- *     if (!canEnterCallback)
- *         return;
- *
- * 	   // Do your thing.
- * }
- * @endcode
- * There are probably many ways to improve these and probably even debug them.
- * The spinlocking itself could be integrated in the constructor, although the
- * check for return in the callback could not.
- */
-#include <atomic>
-
-namespace sfz
-{
-/**
- * @brief Simple class to set an atomic to true and automatically set it back to false on
- * destruction.
- *
- * You call it like this assuming you need indicate that you are in e.g. a callback
- * @code{.cpp}
- * void functionToProtect()
- * {
- * 		AtomicGuard { guard };
- *
- * 		// Do stuff, the atomic will be set back to false as soon as you're back
- * }
- * @endcode
- * Note that this is not thread-safe at all, in the sense that it is only meant to be
- * used with 2 threads along with the AtomicDisabler. One thread uses AtomicGuards, the other
- * AtomicDisablers, and no other contending thread can share this pair of atomics.
- */
-class AtomicGuard
-{
-public:
-	AtomicGuard() = delete;
-	AtomicGuard(std::atomic<bool>& guard)
-	: guard(guard)
-	{
-		guard = true;
-	}
-	~AtomicGuard()
-	{
-		guard = false;
-	}
-private:
-	std::atomic<bool>& guard;
-};
-
-/**
- * @brief Simple class to set an atomic to false and automatically set it back to true on
- * destruction.
- *
- * You call it like this assuming you need to disable e.g. a callback
- * @code{.cpp}
- * void functionThatDisableAnotherFunction()
- * {
- * 		AtomicDisabler { disabler };
- *
- * 		// Do stuff, the atomic will be set back to true as soon as you're back
- * }
- * @endcode
- * Note that this is not thread-safe at all, in the sense that it is only meant to be
- * used with 2 threads along with the AtomicGuard. One thread uses AtomicGuards, the other
- * AtomicDisabler, and no other contending thread can share this pair of atomics.
- */
-class AtomicDisabler
-{
-public:
-	AtomicDisabler() = delete;
-	AtomicDisabler(std::atomic<bool>& allowed)
-	: allowed(allowed)
-	{
-		allowed = false;
-	}
-	~AtomicDisabler()
-	{
-		allowed = true;
-	}
-private:
-	std::atomic<bool>& allowed;
-};
-}
diff --git a/src/sfizz/EQPool.cpp b/src/sfizz/EQPool.cpp
index 515f26ef..65d5866c 100644
--- a/src/sfizz/EQPool.cpp
+++ b/src/sfizz/EQPool.cpp
@@ -1,5 +1,4 @@
 #include "EQPool.h"
-#include "AtomicGuard.h"
 #include <thread>
 #include "absl/algorithm/container.h"
 #include "SIMDHelpers.h"
@@ -108,8 +107,8 @@ sfz::EQPool::EQPool(const MidiState& state, int numEQs)
 
 sfz::EQHolderPtr sfz::EQPool::getEQ(const EQDescription& description, unsigned numChannels, float velocity)
 {
-    AtomicGuard guard { givingOutEQs };
-    if (!canGiveOutEQs)
+    const std::unique_lock<std::mutex> lock { eqGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return {};
 
     auto eq = absl::c_find_if(eqs, [](const EQHolderPtr& holder) {
@@ -132,10 +131,7 @@ size_t sfz::EQPool::getActiveEQs() const
 
 size_t sfz::EQPool::setnumEQs(size_t numEQs)
 {
-    AtomicDisabler disabler { canGiveOutEQs };
-
-    while(givingOutEQs)
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    const std::lock_guard<std::mutex> eqLock { eqGuard };
 
     auto eqIterator = eqs.begin();
     auto eqSentinel = eqs.rbegin();
diff --git a/src/sfizz/EQPool.h b/src/sfizz/EQPool.h
index 9890c10a..7c70af22 100644
--- a/src/sfizz/EQPool.h
+++ b/src/sfizz/EQPool.h
@@ -4,6 +4,7 @@
 #include "MidiState.h"
 #include <vector>
 #include <memory>
+#include <mutex>
 
 namespace sfz
 {
@@ -114,8 +115,7 @@ public:
      */
     void setSampleRate(float sampleRate);
 private:
-    std::atomic<bool> givingOutEQs { false };
-    std::atomic<bool> canGiveOutEQs { true };
+    std::mutex eqGuard;
     float sampleRate { config::defaultSampleRate };
     const MidiState& midiState;
     std::vector<EQHolderPtr> eqs;
diff --git a/src/sfizz/FilePool.cpp b/src/sfizz/FilePool.cpp
index 9b43a2be..c474b634 100644
--- a/src/sfizz/FilePool.cpp
+++ b/src/sfizz/FilePool.cpp
@@ -29,7 +29,6 @@
 #include "Config.h"
 #include "Debug.h"
 #include "Oversampler.h"
-#include "AtomicGuard.h"
 #include "absl/types/span.h"
 #include "absl/strings/match.h"
 #include "absl/memory/memory.h"
@@ -106,6 +105,12 @@ sfz::FilePool::FilePool(sfz::Logger& logger)
 sfz::FilePool::~FilePool()
 {
     quitThread = true;
+
+    for (unsigned i = 0; i < threadPool.size(); ++i) {
+        std::error_code ec;
+        workerBarrier.post(ec);
+    }
+
     for (auto& thread: threadPool)
         thread.join();
 }
@@ -282,7 +287,12 @@ sfz::FilePromisePtr sfz::FilePool::getFilePromise(const std::string& filename) n
         return {};
     }
 
+    std::error_code ec;
+    workerBarrier.post(ec);
+    ASSERT(!ec);
+
     emptyPromises.pop_back();
+
     return promise;
 }
 
@@ -301,10 +311,7 @@ void sfz::FilePool::setPreloadSize(uint32_t preloadSize) noexcept
 
 void sfz::FilePool::tryToClearPromises()
 {
-    AtomicDisabler disabler { canAddPromisesToClear };
-
-    while (addingPromisesToClear)
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    const std::lock_guard<std::mutex> promiseLock { promiseGuard };
 
     for (auto& promise: promisesToClear) {
         if (promise->dataStatus != FilePromise::DataStatus::Wait)
@@ -333,8 +340,11 @@ void sfz::FilePool::loadingThread() noexcept
             continue;
         }
 
+        std::error_code ec;
+        workerBarrier.wait(ec);
+        ASSERT(!ec);
+
         if (!promiseQueue.try_pop(promise)) {
-            std::this_thread::sleep_for(std::chrono::milliseconds(1));
             continue;
         }
 
@@ -376,9 +386,8 @@ void sfz::FilePool::clear()
 
 void sfz::FilePool::cleanupPromises() noexcept
 {
-    AtomicGuard guard { addingPromisesToClear };
-
-    if (!canAddPromisesToClear)
+    const std::unique_lock<std::mutex> lock { promiseGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return;
 
     // The garbage collection cleared the data from these so we can move them
@@ -444,6 +453,10 @@ uint32_t sfz::FilePool::getPreloadSize() const noexcept
 void sfz::FilePool::emptyFileLoadingQueues() noexcept
 {
     emptyQueue = true;
+    std::error_code ec;
+    workerBarrier.post(ec);
+    ASSERT(!ec);
+
     while (emptyQueue)
         std::this_thread::sleep_for(std::chrono::milliseconds(1));
 }
diff --git a/src/sfizz/FilePool.h b/src/sfizz/FilePool.h
index 450a4c24..c2600ece 100644
--- a/src/sfizz/FilePool.h
+++ b/src/sfizz/FilePool.h
@@ -27,6 +27,7 @@
 #include "Config.h"
 #include "Defaults.h"
 #include "LeakDetector.h"
+#include "RTSemaphore.h"
 #include "AudioBuffer.h"
 #include "AudioSpan.h"
 #include "SIMDHelpers.h"
@@ -38,6 +39,7 @@
 #include "Logger.h"
 #include <chrono>
 #include <thread>
+#include <mutex>
 
 namespace sfz {
 using AudioBufferPtr = std::shared_ptr<AudioBuffer<float>>;
@@ -256,16 +258,16 @@ private:
     uint32_t preloadSize { config::preloadSize };
     Oversampling oversamplingFactor { config::defaultOversamplingFactor };
     // Signals
-    bool quitThread { false };
-    bool emptyQueue { false };
+    volatile bool quitThread { false };
+    volatile bool emptyQueue { false };
     std::atomic<int> threadsLoading { 0 };
+    RTSemaphore workerBarrier;
 
     // File promises data structures along with their guards.
     std::vector<FilePromisePtr> emptyPromises;
     std::vector<FilePromisePtr> temporaryFilePromises;
     std::vector<FilePromisePtr> promisesToClear;
-    std::atomic<bool> addingPromisesToClear { false };
-    std::atomic<bool> canAddPromisesToClear { true };
+    std::mutex promiseGuard;
 
     // Preloaded data
     absl::flat_hash_map<absl::string_view, FileDataHandle> preloadedFiles;
diff --git a/src/sfizz/FilterPool.cpp b/src/sfizz/FilterPool.cpp
index 062e4e95..9e4f9091 100644
--- a/src/sfizz/FilterPool.cpp
+++ b/src/sfizz/FilterPool.cpp
@@ -1,7 +1,6 @@
 #include "FilterPool.h"
 #include "SIMDHelpers.h"
 #include "absl/algorithm/container.h"
-#include "AtomicGuard.h"
 #include <thread>
 #include <chrono>
 
@@ -109,8 +108,8 @@ sfz::FilterPool::FilterPool(const MidiState& state, int numFilters)
 
 sfz::FilterHolderPtr sfz::FilterPool::getFilter(const FilterDescription& description, unsigned numChannels, int noteNumber, float velocity)
 {
-    AtomicGuard guard { givingOutFilters };
-    if (!canGiveOutFilters)
+    const std::unique_lock<std::mutex> lock { filterGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return {};
 
     auto filter = absl::c_find_if(filters, [](const FilterHolderPtr& holder) {
@@ -133,10 +132,7 @@ size_t sfz::FilterPool::getActiveFilters() const
 
 size_t sfz::FilterPool::setNumFilters(size_t numFilters)
 {
-    AtomicDisabler disabler { canGiveOutFilters };
-
-    while(givingOutFilters)
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    const std::lock_guard<std::mutex> filterLock { filterGuard };
 
     auto filterIterator = filters.begin();
     auto filterSentinel = filters.rbegin();
diff --git a/src/sfizz/FilterPool.h b/src/sfizz/FilterPool.h
index fb1a8aac..25ba0215 100644
--- a/src/sfizz/FilterPool.h
+++ b/src/sfizz/FilterPool.h
@@ -4,6 +4,7 @@
 #include "MidiState.h"
 #include <vector>
 #include <memory>
+#include <mutex>
 
 namespace sfz
 {
@@ -118,8 +119,7 @@ public:
      */
     void setSampleRate(float sampleRate);
 private:
-    std::atomic<bool> givingOutFilters { false };
-    std::atomic<bool> canGiveOutFilters { true };
+    std::mutex filterGuard;
     float sampleRate { config::defaultSampleRate };
     const MidiState& midiState;
     std::vector<FilterHolderPtr> filters;
diff --git a/src/sfizz/RTSemaphore.cpp b/src/sfizz/RTSemaphore.cpp
index 7a3340d5..685166e4 100644
--- a/src/sfizz/RTSemaphore.cpp
+++ b/src/sfizz/RTSemaphore.cpp
@@ -18,7 +18,7 @@ RTSemaphore::RTSemaphore(unsigned value)
     good_ = true;
 }
 
-RTSemaphore::RTSemaphore(std::error_code &ec, unsigned value) noexcept
+RTSemaphore::RTSemaphore(std::error_code& ec, unsigned value) noexcept
 {
     init(ec, value);
     good_ = ec ? false : true;
@@ -58,7 +58,7 @@ bool RTSemaphore::try_wait()
 }
 
 #if defined(__APPLE__)
-void RTSemaphore::init(std::error_code &ec, unsigned value)
+void RTSemaphore::init(std::error_code& ec, unsigned value)
 {
     ec.clear();
     kern_return_t ret = semaphore_create(mach_task_self(), &sem_, SYNC_POLICY_FIFO, value);
@@ -66,7 +66,7 @@ void RTSemaphore::init(std::error_code &ec, unsigned value)
         ec = std::error_code(ret, mach_category());
 }
 
-void RTSemaphore::destroy(std::error_code &ec)
+void RTSemaphore::destroy(std::error_code& ec)
 {
     ec.clear();
     kern_return_t ret = semaphore_destroy(mach_task_self(), sem_);
@@ -74,7 +74,7 @@ void RTSemaphore::destroy(std::error_code &ec)
         ec = std::error_code(ret, mach_category());
 }
 
-void RTSemaphore::post(std::error_code &ec) noexcept
+void RTSemaphore::post(std::error_code& ec) noexcept
 {
     ec.clear();
     kern_return_t ret = semaphore_signal(sem_);
@@ -82,7 +82,7 @@ void RTSemaphore::post(std::error_code &ec) noexcept
         ec = std::error_code(ret, mach_category());
 }
 
-void RTSemaphore::wait(std::error_code &ec) noexcept
+void RTSemaphore::wait(std::error_code& ec) noexcept
 {
     ec.clear();
     do {
@@ -99,11 +99,11 @@ void RTSemaphore::wait(std::error_code &ec) noexcept
     } while (1);
 }
 
-bool RTSemaphore::try_wait(std::error_code &ec) noexcept
+bool RTSemaphore::try_wait(std::error_code& ec) noexcept
 {
     ec.clear();
     do {
-        const mach_timespec_t timeout = {0, 0};
+        const mach_timespec_t timeout = { 0, 0 };
         kern_return_t ret = semaphore_timedwait(sem_, timeout);
         switch (ret) {
         case KERN_SUCCESS:
@@ -119,18 +119,18 @@ bool RTSemaphore::try_wait(std::error_code &ec) noexcept
     } while (1);
 }
 
-const std::error_category &RTSemaphore::mach_category()
+const std::error_category& RTSemaphore::mach_category()
 {
     class mach_category : public std::error_category {
     public:
-        const char *name() const noexcept override
+        const char* name() const noexcept override
         {
             return "kern_return_t";
         }
 
         std::string message(int condition) const override
         {
-            const char *str = mach_error_string(condition);
+            const char* str = mach_error_string(condition);
             return str ? str : "";
         }
     };
@@ -139,7 +139,7 @@ const std::error_category &RTSemaphore::mach_category()
     return cat;
 }
 #elif defined(_WIN32)
-void RTSemaphore::init(std::error_code &ec, unsigned value)
+void RTSemaphore::init(std::error_code& ec, unsigned value)
 {
     ec.clear();
     sem_ = CreateSemaphore(nullptr, value, LONG_MAX, nullptr);
@@ -147,21 +147,21 @@ void RTSemaphore::init(std::error_code &ec, unsigned value)
         ec = std::error_code(GetLastError(), std::system_category());
 }
 
-void RTSemaphore::destroy(std::error_code &ec)
+void RTSemaphore::destroy(std::error_code& ec)
 {
     ec.clear();
     if (CloseHandle(sem_) == 0)
         ec = std::error_code(GetLastError(), std::system_category());
 }
 
-void RTSemaphore::post(std::error_code &ec) noexcept
+void RTSemaphore::post(std::error_code& ec) noexcept
 {
     ec.clear();
     if (ReleaseSemaphore(sem_, 1, nullptr) == 0)
         ec = std::error_code(GetLastError(), std::system_category());
 }
 
-void RTSemaphore::wait(std::error_code &ec) noexcept
+void RTSemaphore::wait(std::error_code& ec) noexcept
 {
     ec.clear();
     DWORD ret = WaitForSingleObject(sem_, INFINITE);
@@ -177,7 +177,7 @@ void RTSemaphore::wait(std::error_code &ec) noexcept
     }
 }
 
-bool RTSemaphore::try_wait(std::error_code &ec) noexcept
+bool RTSemaphore::try_wait(std::error_code& ec) noexcept
 {
     ec.clear();
     DWORD ret = WaitForSingleObject(sem_, 0);
@@ -195,21 +195,21 @@ bool RTSemaphore::try_wait(std::error_code &ec) noexcept
     }
 }
 #else
-void RTSemaphore::init(std::error_code &ec, unsigned value)
+void RTSemaphore::init(std::error_code& ec, unsigned value)
 {
     ec.clear();
     if (sem_init(&sem_, 0, value) != 0)
         ec = std::error_code(errno, std::generic_category());
 }
 
-void RTSemaphore::destroy(std::error_code &ec)
+void RTSemaphore::destroy(std::error_code& ec)
 {
     ec.clear();
     if (sem_destroy(&sem_) != 0)
         ec = std::error_code(errno, std::generic_category());
 }
 
-void RTSemaphore::post(std::error_code &ec) noexcept
+void RTSemaphore::post(std::error_code& ec) noexcept
 {
     ec.clear();
     while (sem_post(&sem_) != 0) {
@@ -221,7 +221,7 @@ void RTSemaphore::post(std::error_code &ec) noexcept
     }
 }
 
-void RTSemaphore::wait(std::error_code &ec) noexcept
+void RTSemaphore::wait(std::error_code& ec) noexcept
 {
     ec.clear();
     while (sem_wait(&sem_) != 0) {
@@ -233,7 +233,7 @@ void RTSemaphore::wait(std::error_code &ec) noexcept
     }
 }
 
-bool RTSemaphore::try_wait(std::error_code &ec) noexcept
+bool RTSemaphore::try_wait(std::error_code& ec) noexcept
 {
     ec.clear();
     do {
diff --git a/src/sfizz/RTSemaphore.h b/src/sfizz/RTSemaphore.h
index 4ce01112..c17e5c2a 100644
--- a/src/sfizz/RTSemaphore.h
+++ b/src/sfizz/RTSemaphore.h
@@ -17,11 +17,11 @@
 class RTSemaphore {
 public:
     explicit RTSemaphore(unsigned value = 0);
-    explicit RTSemaphore(std::error_code &ec, unsigned value = 0) noexcept;
+    explicit RTSemaphore(std::error_code& ec, unsigned value = 0) noexcept;
     ~RTSemaphore() noexcept;
 
-    RTSemaphore(const RTSemaphore &) = delete;
-    RTSemaphore &operator=(const RTSemaphore &) = delete;
+    RTSemaphore(const RTSemaphore&) = delete;
+    RTSemaphore& operator=(const RTSemaphore&) = delete;
 
     explicit operator bool() const noexcept { return good_; }
 
@@ -29,18 +29,18 @@ public:
     void wait();
     bool try_wait();
 
-    void post(std::error_code &ec) noexcept;
-    void wait(std::error_code &ec) noexcept;
-    bool try_wait(std::error_code &ec) noexcept;
+    void post(std::error_code& ec) noexcept;
+    void wait(std::error_code& ec) noexcept;
+    bool try_wait(std::error_code& ec) noexcept;
 
 private:
-    void init(std::error_code &ec, unsigned value);
-    void destroy(std::error_code &ec);
+    void init(std::error_code& ec, unsigned value);
+    void destroy(std::error_code& ec);
 
 private:
 #if defined(__APPLE__)
     semaphore_t sem_ {};
-    static const std::error_category &mach_category();
+    static const std::error_category& mach_category();
 #elif defined(_WIN32)
     HANDLE sem_ {};
 #else
diff --git a/src/sfizz/Synth.cpp b/src/sfizz/Synth.cpp
index 52dfba4c..1141624c 100644
--- a/src/sfizz/Synth.cpp
+++ b/src/sfizz/Synth.cpp
@@ -5,7 +5,6 @@
 // If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
 
 #include "Synth.h"
-#include "AtomicGuard.h"
 #include "Config.h"
 #include "Debug.h"
 #include "Macros.h"
@@ -28,21 +27,16 @@ sfz::Synth::Synth()
 
 sfz::Synth::Synth(int numVoices)
 {
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
     parser.setListener(this);
-
     effectFactory.registerStandardEffectTypes();
-
     effectBuses.reserve(5); // sufficient room for main and fx1-4
-
     resetVoices(numVoices);
 }
 
 sfz::Synth::~Synth()
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
 
     for (auto& voice : voices)
         voice->reset();
@@ -128,10 +122,7 @@ void sfz::Synth::buildRegion(const std::vector<Opcode>& regionOpcodes)
 
 void sfz::Synth::clear()
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
 
     for (auto& voice : voices)
         voice->reset();
@@ -327,13 +318,9 @@ void addEndpointsToVelocityCurve(sfz::Region& region)
 
 bool sfz::Synth::loadSfzFile(const fs::path& file)
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
-
     clear();
 
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
     parser.parseFile(file);
     if (parser.getErrorCount() > 0)
         return false;
@@ -508,11 +495,7 @@ void sfz::Synth::setSamplesPerBlock(int samplesPerBlock) noexcept
 {
     ASSERT(samplesPerBlock < config::maxBlockSize);
 
-    AtomicDisabler callbackDisabler { canEnterCallback };
-
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
 
     this->samplesPerBlock = samplesPerBlock;
     for (auto& voice : voices)
@@ -528,10 +511,7 @@ void sfz::Synth::setSamplesPerBlock(int samplesPerBlock) noexcept
 
 void sfz::Synth::setSampleRate(float sampleRate) noexcept
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
 
     this->sampleRate = sampleRate;
     for (auto& voice : voices)
@@ -558,9 +538,8 @@ void sfz::Synth::renderBlock(AudioSpan<float> buffer) noexcept
     if (freeWheeling)
         resources.filePool.waitForBackgroundLoading();
 
-
-    AtomicGuard callbackGuard { inCallback };
-    if (!canEnterCallback)
+    const std::unique_lock<std::mutex> lock { callbackGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return;
 
 
@@ -655,8 +634,8 @@ void sfz::Synth::noteOn(int delay, int noteNumber, uint8_t velocity) noexcept
     ScopedTiming logger { dispatchDuration, ScopedTiming::Operation::addToDuration };
     resources.midiState.noteOnEvent(delay, noteNumber, normalizedVelocity);
 
-    AtomicGuard callbackGuard { inCallback };
-    if (!canEnterCallback)
+    const std::unique_lock<std::mutex> lock { callbackGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return;
 
     noteOnDispatch(delay, noteNumber, normalizedVelocity);
@@ -671,8 +650,8 @@ void sfz::Synth::noteOff(int delay, int noteNumber, uint8_t velocity) noexcept
     ScopedTiming logger { dispatchDuration, ScopedTiming::Operation::addToDuration };
     resources.midiState.noteOffEvent(delay, noteNumber, normalizedVelocity);
 
-    AtomicGuard callbackGuard { inCallback };
-    if (!canEnterCallback)
+    const std::unique_lock<std::mutex> lock { callbackGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return;
 
     // FIXME: Some keyboards (e.g. Casio PX5S) can send a real note-off velocity. In this case, do we have a
@@ -767,8 +746,8 @@ void sfz::Synth::cc(int delay, int ccNumber, uint8_t ccValue) noexcept
     ScopedTiming logger { dispatchDuration, ScopedTiming::Operation::addToDuration };
     resources.midiState.ccEvent(delay, ccNumber, normalizedCC);
 
-    AtomicGuard callbackGuard { inCallback };
-    if (!canEnterCallback)
+    const std::unique_lock<std::mutex> lock { callbackGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return;
 
     if (ccNumber == config::resetCC) {
@@ -961,16 +940,12 @@ int sfz::Synth::getNumVoices() const noexcept
 void sfz::Synth::setNumVoices(int numVoices) noexcept
 {
     ASSERT(numVoices > 0);
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
     resetVoices(numVoices);
 }
 
 void sfz::Synth::resetVoices(int numVoices)
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
-
     voices.clear();
     for (int i = 0; i < numVoices; ++i)
         voices.push_back(absl::make_unique<Voice>(resources));
@@ -986,10 +961,7 @@ void sfz::Synth::resetVoices(int numVoices)
 
 void sfz::Synth::setOversamplingFactor(sfz::Oversampling factor) noexcept
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
 
     for (auto& voice : voices)
         voice->reset();
@@ -1006,10 +978,7 @@ sfz::Oversampling sfz::Synth::getOversamplingFactor() const noexcept
 
 void sfz::Synth::setPreloadSize(uint32_t preloadSize) noexcept
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
 
     resources.filePool.setPreloadSize(preloadSize);
 }
@@ -1036,11 +1005,12 @@ void sfz::Synth::disableFreeWheeling() noexcept
 
 void sfz::Synth::resetAllControllers(int delay) noexcept
 {
-    AtomicGuard callbackGuard { inCallback };
-    if (!canEnterCallback)
+    resources.midiState.resetAllControllers(delay);
+
+    const std::unique_lock<std::mutex> lock { callbackGuard, std::try_to_lock };
+    if (!lock.owns_lock())
         return;
 
-    resources.midiState.resetAllControllers(delay);
     for (auto& voice : voices) {
         voice->registerPitchWheel(delay, 0);
         for (int cc = 0; cc < config::numCCs; ++cc)
@@ -1086,10 +1056,7 @@ void sfz::Synth::disableLogging() noexcept
 
 void sfz::Synth::allSoundOff() noexcept
 {
-    AtomicDisabler callbackDisabler { canEnterCallback };
-    while (inCallback) {
-        std::this_thread::sleep_for(std::chrono::milliseconds(1));
-    }
+    const std::lock_guard<std::mutex> disableCallback { callbackGuard };
 
     for (auto& voice : voices)
         voice->reset();
diff --git a/src/sfizz/Synth.h b/src/sfizz/Synth.h
index 16017f3a..6b3d4c37 100644
--- a/src/sfizz/Synth.h
+++ b/src/sfizz/Synth.h
@@ -18,6 +18,7 @@
 #include "absl/types/span.h"
 #include <absl/types/optional.h>
 #include <random>
+#include <mutex>
 #include <set>
 #include <string_view>
 #include <vector>
@@ -436,13 +437,7 @@ private:
      *
      */
     void clear();
-    /**
-     * @brief Resets and possibly changes the number of voices (polyphony) in
-     * the synth.
-     *
-     * @param numVoices
-     */
-    void resetVoices(int numVoices);
+
     /**
      * @brief Helper function to dispatch <global> opcodes
      *
@@ -475,6 +470,13 @@ private:
      * @param regionOpcodes the opcodes that are specific to the region
      */
     void buildRegion(const std::vector<Opcode>& regionOpcodes);
+    /**
+     * @brief Resets and possibly changes the number of voices (polyphony) in
+     * the synth.
+     *
+     * @param numVoices
+     */
+    void resetVoices(int numVoices);
 
     fs::file_time_type checkModificationTime();
 
@@ -526,9 +528,7 @@ private:
     std::uniform_real_distribution<float> randNoteDistribution { 0, 1 };
     unsigned fileTicket { 1 };
 
-    // Atomic guards; must be used with AtomicGuard and AtomicDisabler
-    std::atomic<bool> canEnterCallback { true };
-    std::atomic<bool> inCallback { false };
+    std::mutex callbackGuard;
     bool freeWheeling { false };
 
     // Singletons passed as references to the voices
diff --git a/tests/FilesT.cpp b/tests/FilesT.cpp
index 75941298..2442d8df 100644
--- a/tests/FilesT.cpp
+++ b/tests/FilesT.cpp
@@ -532,8 +532,7 @@ TEST_CASE("[Files] Looped regions taken from files and possibly overriden")
 
 TEST_CASE("[Files] Case sentitiveness")
 {
-    const fs::path sfzFilePath = fs::current_path() /
-        "tests/TestFiles/case_insensitive.sfz";
+    const fs::path sfzFilePath = fs::current_path() / "tests/TestFiles/case_insensitive.sfz";
 
 #if defined(_WIN32)
     const bool caseSensitiveFs = false;