diff --git a/Makefile b/Makefile
index 1065763..bfd4c37 100644
--- a/Makefile
+++ b/Makefile
@@ -15,7 +15,7 @@ endif
 
 # C++ specific options here (added to USE_OPT).
 ifeq ($(USE_CPPOPT),)
-  USE_CPPOPT = -std=c++23 -fno-exceptions -fno-rtti
+  USE_CPPOPT = -std=c++23 -fno-exceptions -fno-rtti -fno-threadsafe-statics
 endif
 
 # Enable this if you want the linker to remove unused code and data.
diff --git a/main.cpp b/main.cpp
index 2db9ec8..da1722f 100644
--- a/main.cpp
+++ b/main.cpp
@@ -9,9 +9,9 @@
 
 static constexpr auto& WEIGHTING       = A_weighting;
 static constexpr auto& MIC_EQUALIZER   = SPH0645LM4H_B_RB;
-static constexpr float MIC_OFFSET_DB   (  0.f); // Linear offset
-static constexpr float MIC_SENSITIVITY (-26.f); // dBFS value expected at MIC_REF_DB
-static constexpr float MIC_REF_DB      ( 94.f); // dB where sensitivity is specified
+static constexpr sos_t MIC_OFFSET_DB   (  0.f); // Linear offset
+static constexpr sos_t MIC_SENSITIVITY (-26.f); // dBFS value expected at MIC_REF_DB
+static constexpr sos_t MIC_REF_DB      ( 94.f); // dB where sensitivity is specified
 static constexpr sos_t MIC_OVERLOAD_DB (120.f); // dB - Acoustic overload point
 static constexpr sos_t MIC_NOISE_DB    ( 29.f); // dB - Noise floor
 static constexpr auto  MIC_BITS        = 18u;
@@ -21,8 +21,8 @@ static constexpr unsigned I2S_BUFSIZ = 1024;
 static constexpr unsigned I2S_STRIDE = 16;
 
 // Calculate reference amplitude value at compile time
-static const auto MIC_REF_AMPL = qfp_fpow(10.f, MIC_SENSITIVITY / 20) *
-    ((1 << (MIC_BITS - 1)) - 1);
+static const auto MIC_REF_AMPL = sos_t((1 << (MIC_BITS - 1)) - 1) *
+    qfp_fpow(10.f, MIC_SENSITIVITY / 20.f);
 
 static SEMAPHORE_DECL(i2sReady, 0);
 static THD_WORKING_AREA(waThread1, 128);
@@ -83,13 +83,13 @@ THD_FUNCTION(Thread1, arg)
         palSetPad(GPIOB, 7);
         chSemWait(&i2sReady);
 
-        const auto Leq_RMS = qfp_fsqrt((float)Leq_sum_sqr / Leq_samples);
-        const auto Leq_dB = MIC_OFFSET_DB + MIC_REF_DB + 20 *
+        const sos_t Leq_RMS = qfp_fsqrt(Leq_sum_sqr / qfp_uint2float(Leq_samples));
+        const sos_t Leq_dB = MIC_OFFSET_DB + MIC_REF_DB + sos_t(20.f) *
             qfp_flog10(Leq_RMS / MIC_REF_AMPL);
         Leq_sum_sqr = sos_t(0.f);
         Leq_samples = 0;
 
-        auto n = std::clamp(static_cast<int32_t>(Leq_dB), 0l, 999l);
+        auto n = std::clamp(qfp_float2int(Leq_dB), 0, 999);
         strbuf[2] = n % 10 + '0'; n /= 10;
         strbuf[1] = n % 10 + '0'; n /= 10;
         strbuf[0] = n ? n + '0' : ' ';
@@ -111,7 +111,7 @@ void i2sCallback(I2SDriver *i2s)
     std::ranges::copy(
         std::views::counted(i2sBuffer.begin() + offset, halfsize / I2S_STRIDE)
             | std::ranges::views::stride(2)
-            | std::views::transform([](uint32_t s) { return sos_t(fixsample(s)); }),
+            | std::views::transform([](uint32_t s) { return sos_t(qfp_int2float(fixsample(s))); }),
         samples);
     auto samps = std::views::counted(samples, halfsize / (2 * I2S_STRIDE));
 
diff --git a/sos-iir-filter.h b/sos-iir-filter.h
index 4d345f1..c827ef9 100644
--- a/sos-iir-filter.h
+++ b/sos-iir-filter.h
@@ -32,34 +32,36 @@ extern "C" {
 
 float qfp_fpow(float b, float e)
 {
-    return qfp_fexp(e * qfp_fln(b));
+    return qfp_fexp(qfp_fmul(e, qfp_fln(b)));
 }
 
 float qfp_flog10(float x)
 {
-    return qfp_fln(x) / qfp_fln(10);
+    static const auto ln10 = qfp_fln(10.f);
+    return qfp_fdiv(qfp_fln(x), ln10);
 }
 
-struct sos_t
+class sos_t
 {
     float v;
 
+public:
     constexpr sos_t(float v_ = 0.f): v(v_) {}
 
-    sos_t operator+(const sos_t& o) const noexcept {
-        return qfp_fadd(v, o.v);
+    sos_t operator+(auto x) const noexcept {
+        return qfp_fadd(v, x);
     }
 
     sos_t operator-(const sos_t& o) const noexcept {
         return qfp_fsub(v, o.v);
     }
 
-    sos_t operator*(const sos_t& o) const noexcept {
-        return qfp_fmul(v, o.v);
+    sos_t operator*(auto x) const noexcept {
+        return qfp_fmul(v, x);
     }
 
-    sos_t operator/(const sos_t& o) const noexcept {
-        return qfp_fdiv(v, o.v);
+    sos_t operator/(auto x) const noexcept {
+        return qfp_fdiv(v, x);
     }
 
     sos_t& operator+=(const sos_t& o) noexcept {
@@ -100,17 +102,14 @@ struct SOS_IIR_Filter {
   }
 
   void filter(auto samples, std::size_t n = N) {
-    for ([[maybe_unused]] auto _ : std::views::zip_transform(
-        [](auto samps, const auto& coeffs, auto& ww) {
-            // Assumes a0 and b0 coefficients are one (1.0)
-            for (auto& s : samps) {
-              auto f6 = s + coeffs.a1 * ww.w0 + coeffs.a2 * ww.w1;
-              s = f6 + coeffs.b1 * ww.w0 + coeffs.b2 * ww.w1;
-              ww.w1 = std::exchange(ww.w0, f6);
-            }
-            return 0;
-        },
-        std::views::repeat(samples, n), sos, w)) {}
+    for (auto [coeffs, ww] : std::views::zip(sos, w) | std::views::take(n)) {
+        // Assumes a0 and b0 coefficients are one (1.0)
+        for (auto& s : samples) {
+            auto f6 = s + coeffs.a1 * ww.w0 + coeffs.a2 * ww.w1;
+            s = f6 + coeffs.b1 * ww.w0 + coeffs.b2 * ww.w1;
+            ww.w1 = std::exchange(ww.w0, f6);
+        }
+    }
   }
 
   sos_t filter_sum_sqr(auto samples) {