diff --git a/src/blacksound/dsp/biquadfilter.cpp b/src/blacksound/dsp/biquadfilter.cpp
index 35459e788..e19a2e74a 100644
--- a/src/blacksound/dsp/biquadfilter.cpp
+++ b/src/blacksound/dsp/biquadfilter.cpp
@@ -1,101 +1,116 @@
+/* Copyright (C) 2019
+ * swift project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution. No part of swift project, including this file, may be copied, modified, propagated,
+ * or distributed except according to the terms contained in the LICENSE file.
+ */
+
 #include "biquadfilter.h"
 
 #include <QtMath>
 #include <algorithm>
 
-float BiQuadFilter::transform(float inSample)
+
+namespace BlackSound
 {
-    // compute result
-    double result = a0 * inSample + a1 * x1 + a2 * x2 - a3 * y1 - a4 * y2;
+    namespace Dsp
+    {
+        float BiQuadFilter::transform(float inSample)
+        {
+            // compute result
+            double result = a0 * inSample + a1 * x1 + a2 * x2 - a3 * y1 - a4 * y2;
 
-    // shift x1 to x2, sample to x1
-    x2 = x1;
-    x1 = inSample;
+            // shift x1 to x2, sample to x1
+            x2 = x1;
+            x1 = inSample;
 
-    // shift y1 to y2, result to y1
-    y2 = y1;
-    y1 = (float)result;
+            // shift y1 to y2, result to y1
+            y2 = y1;
+            y1 = static_cast<float>(result);
 
-    return y1;
-}
+            return y1;
+        }
 
-void BiQuadFilter::setCoefficients(double aa0, double aa1, double aa2, double b0, double b1, double b2)
-{
-    // precompute the coefficients
-    a0 = b0 / aa0;
-    a1 = b1 / aa0;
-    a2 = b2 / aa0;
-    a3 = aa1 / aa0;
-    a4 = aa2 / aa0;
-}
+        void BiQuadFilter::setCoefficients(double aa0, double aa1, double aa2, double b0, double b1, double b2)
+        {
+            // precompute the coefficients
+            a0 = b0 / aa0;
+            a1 = b1 / aa0;
+            a2 = b2 / aa0;
+            a3 = aa1 / aa0;
+            a4 = aa2 / aa0;
+        }
 
-void BiQuadFilter::setLowPassFilter(float sampleRate, float cutoffFrequency, float q)
-{
-    // H(s) = 1 / (s^2 + s/Q + 1)
-    auto w0 = 2 * M_PI * cutoffFrequency / sampleRate;
-    auto cosw0 = qCos(w0);
-    auto alpha = qSin(w0) / (2 * q);
+        void BiQuadFilter::setLowPassFilter(float sampleRate, float cutoffFrequency, float q)
+        {
+            // H(s) = 1 / (s^2 + s/Q + 1)
+            auto w0 = 2 * M_PI * cutoffFrequency / sampleRate;
+            auto cosw0 = qCos(w0);
+            auto alpha = qSin(w0) / (2 * q);
 
-    auto b0 = (1 - cosw0) / 2;
-    auto b1 = 1 - cosw0;
-    auto b2 = (1 - cosw0) / 2;
-    auto aa0 = 1 + alpha;
-    auto aa1 = -2 * cosw0;
-    auto aa2 = 1 - alpha;
-    setCoefficients(aa0, aa1, aa2, b0, b1, b2);
-}
+            auto b0 = (1 - cosw0) / 2;
+            auto b1 = 1 - cosw0;
+            auto b2 = (1 - cosw0) / 2;
+            auto aa0 = 1 + alpha;
+            auto aa1 = -2 * cosw0;
+            auto aa2 = 1 - alpha;
+            setCoefficients(aa0, aa1, aa2, b0, b1, b2);
+        }
 
-void BiQuadFilter::setPeakingEq(float sampleRate, float centreFrequency, float q, float dbGain)
-{
-    // H(s) = (s^2 + s*(A/Q) + 1) / (s^2 + s/(A*Q) + 1)
-    auto w0 = 2 * M_PI * centreFrequency / sampleRate;
-    auto cosw0 = qCos(w0);
-    auto sinw0 = qSin(w0);
-    auto alpha = sinw0 / (2 * q);
-    auto a = qPow(10, dbGain / 40);     // TODO: should we square root this value?
+        void BiQuadFilter::setPeakingEq(float sampleRate, float centreFrequency, float q, float dbGain)
+        {
+            // H(s) = (s^2 + s*(A/Q) + 1) / (s^2 + s/(A*Q) + 1)
+            auto w0 = 2 * M_PI * centreFrequency / sampleRate;
+            auto cosw0 = qCos(w0);
+            auto sinw0 = qSin(w0);
+            auto alpha = sinw0 / (2 * q);
+            auto a = qPow(10, dbGain / 40);     // TODO: should we square root this value?
 
-    auto b0 = 1 + alpha * a;
-    auto b1 = -2 * cosw0;
-    auto b2 = 1 - alpha * a;
-    auto aa0 = 1 + alpha / a;
-    auto aa1 = -2 * cosw0;
-    auto aa2 = 1 - alpha / a;
-    setCoefficients(aa0, aa1, aa2, b0, b1, b2);
-}
+            auto b0 = 1 + alpha * a;
+            auto b1 = -2 * cosw0;
+            auto b2 = 1 - alpha * a;
+            auto aa0 = 1 + alpha / a;
+            auto aa1 = -2 * cosw0;
+            auto aa2 = 1 - alpha / a;
+            setCoefficients(aa0, aa1, aa2, b0, b1, b2);
+        }
 
-void BiQuadFilter::setHighPassFilter(float sampleRate, float cutoffFrequency, float q)
-{
-    // H(s) = s^2 / (s^2 + s/Q + 1)
-    auto w0 = 2 * M_PI * cutoffFrequency / sampleRate;
-    auto cosw0 = qCos(w0);
-    auto alpha = qSin(w0) / (2 * q);
+        void BiQuadFilter::setHighPassFilter(float sampleRate, float cutoffFrequency, float q)
+        {
+            // H(s) = s^2 / (s^2 + s/Q + 1)
+            auto w0 = 2 * M_PI * cutoffFrequency / sampleRate;
+            auto cosw0 = qCos(w0);
+            auto alpha = qSin(w0) / (2 * q);
 
-    auto b0 = (1 + cosw0) / 2;
-    auto b1 = -(1 + cosw0);
-    auto b2 = (1 + cosw0) / 2;
-    auto aa0 = 1 + alpha;
-    auto aa1 = -2 * cosw0;
-    auto aa2 = 1 - alpha;
-    setCoefficients(aa0, aa1, aa2, b0, b1, b2);
-}
+            auto b0 = (1 + cosw0) / 2;
+            auto b1 = -(1 + cosw0);
+            auto b2 = (1 + cosw0) / 2;
+            auto aa0 = 1 + alpha;
+            auto aa1 = -2 * cosw0;
+            auto aa2 = 1 - alpha;
+            setCoefficients(aa0, aa1, aa2, b0, b1, b2);
+        }
 
-BiQuadFilter BiQuadFilter::lowPassFilter(float sampleRate, float cutoffFrequency, float q)
-{
-    BiQuadFilter filter;
-    filter.setLowPassFilter(sampleRate, cutoffFrequency, q);
-    return filter;
-}
+        BiQuadFilter BiQuadFilter::lowPassFilter(float sampleRate, float cutoffFrequency, float q)
+        {
+            BiQuadFilter filter;
+            filter.setLowPassFilter(sampleRate, cutoffFrequency, q);
+            return filter;
+        }
 
-BiQuadFilter BiQuadFilter::highPassFilter(float sampleRate, float cutoffFrequency, float q)
-{
-    BiQuadFilter filter;
-    filter.setHighPassFilter(sampleRate, cutoffFrequency, q);
-    return filter;
-}
+        BiQuadFilter BiQuadFilter::highPassFilter(float sampleRate, float cutoffFrequency, float q)
+        {
+            BiQuadFilter filter;
+            filter.setHighPassFilter(sampleRate, cutoffFrequency, q);
+            return filter;
+        }
 
-BiQuadFilter BiQuadFilter::peakingEQ(float sampleRate, float centreFrequency, float q, float dbGain)
-{
-    BiQuadFilter filter;
-    filter.setPeakingEq(sampleRate, centreFrequency, q, dbGain);
-    return filter;
-}
+        BiQuadFilter BiQuadFilter::peakingEQ(float sampleRate, float centreFrequency, float q, float dbGain)
+        {
+            BiQuadFilter filter;
+            filter.setPeakingEq(sampleRate, centreFrequency, q, dbGain);
+            return filter;
+        }
+    } // ns
+} // ns
diff --git a/src/blacksound/dsp/biquadfilter.h b/src/blacksound/dsp/biquadfilter.h
index 0bf430804..33fcb7dcd 100644
--- a/src/blacksound/dsp/biquadfilter.h
+++ b/src/blacksound/dsp/biquadfilter.h
@@ -1,35 +1,54 @@
+/* Copyright (C) 2019
+ * swift project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution. No part of swift project, including this file, may be copied, modified, propagated,
+ * or distributed except according to the terms contained in the LICENSE file.
+ */
+
+//! \file
+
 #ifndef BIQUADFILTER_H
 #define BIQUADFILTER_H
 
 #include "blacksound/blacksoundexport.h"
 
-class BiQuadFilter
+namespace BlackSound
 {
-public:
-    BiQuadFilter() = default;
+    namespace Dsp
+    {
+        //! Digital biquad filter
+        class BiQuadFilter
+        {
+        public:
+            //! Ctor
+            BiQuadFilter() = default;
 
-    float transform(float inSample);
-    void setCoefficients(double aa0, double aa1, double aa2, double b0, double b1, double b2);
-    void setLowPassFilter(float sampleRate, float cutoffFrequency, float q);
-    void setPeakingEq(float sampleRate, float centreFrequency, float q, float dbGain);
-    void setHighPassFilter(float sampleRate, float cutoffFrequency, float q);
+            float transform(float inSample);
+            void setCoefficients(double aa0, double aa1, double aa2, double b0, double b1, double b2);
+            void setLowPassFilter(float sampleRate, float cutoffFrequency, float q);
+            void setPeakingEq(float sampleRate, float centreFrequency, float q, float dbGain);
+            void setHighPassFilter(float sampleRate, float cutoffFrequency, float q);
 
-    static BiQuadFilter lowPassFilter(float sampleRate, float cutoffFrequency, float q);
-    static BiQuadFilter highPassFilter(float sampleRate, float cutoffFrequency, float q);
-    static BiQuadFilter peakingEQ(float sampleRate, float centreFrequency, float q, float dbGain);
 
-private:
-    double a0;
-    double a1;
-    double a2;
-    double a3;
-    double a4;
+            static BiQuadFilter lowPassFilter(float sampleRate, float cutoffFrequency, float q);
+            static BiQuadFilter highPassFilter(float sampleRate, float cutoffFrequency, float q);
+            static BiQuadFilter peakingEQ(float sampleRate, float centreFrequency, float q, float dbGain);
 
-    // state
-    float x1 = 0.0;
-    float x2 = 0.0;
-    float y1 = 0.0;
-    float y2 = 0.0;
-};
+        private:
+            double a0;
+            double a1;
+            double a2;
+            double a3;
+            double a4;
 
-#endif // BIQUADFILTER_H
+            // state
+            float x1 = 0.0;
+            float x2 = 0.0;
+            float y1 = 0.0;
+            float y2 = 0.0;
+        };
+    } // ns
+} // ns
+
+#endif // guard
diff --git a/src/blacksound/sampleprovider/equalizersampleprovider.cpp b/src/blacksound/sampleprovider/equalizersampleprovider.cpp
index cecc53d9e..2a37e8cb4 100644
--- a/src/blacksound/sampleprovider/equalizersampleprovider.cpp
+++ b/src/blacksound/sampleprovider/equalizersampleprovider.cpp
@@ -2,6 +2,8 @@
 #include "blacksound/audioutilities.h"
 #include <QDebug>
 
+using namespace BlackSound::Dsp;
+
 namespace BlackSound
 {
     namespace SampleProvider
@@ -52,5 +54,5 @@ namespace BlackSound
         {
             m_outputGain = outputGain;
         }
-    }
-}
+    } // ns
+} // ns
diff --git a/src/blacksound/sampleprovider/equalizersampleprovider.h b/src/blacksound/sampleprovider/equalizersampleprovider.h
index e58870f25..64cfe6d2b 100644
--- a/src/blacksound/sampleprovider/equalizersampleprovider.h
+++ b/src/blacksound/sampleprovider/equalizersampleprovider.h
@@ -52,11 +52,10 @@ namespace BlackSound
             void setupPreset(EqualizerPresets preset);
 
             ISampleProvider *m_sourceProvider = nullptr;
-
-            int    m_channels = 1;
-            bool   m_bypass = false;
+            int    m_channels   = 1;
+            bool   m_bypass     = false;
             double m_outputGain = 1.0;
-            QVector<BiQuadFilter> m_filters;
+            QVector<Dsp::BiQuadFilter> m_filters;
         };
     } // ns
 } // ns