1 files changed, 139 insertions, 0 deletions
diff --git a/arts/modules/synth/synth_compressor_impl.cc b/arts/modules/synth/synth_compressor_impl.cc
new file mode 100644
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+++ b/arts/modules/synth/synth_compressor_impl.cc
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+/*
+
+   Copyright (C) 2001 Matthias Kretz <kretz@kde.org>
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+
+ */
+
+#include "artsmodulessynth.h"
+#include "stdsynthmodule.h"
+#include "debug.h"
+
+#include <math.h>
+#include <string.h>
+
+#ifndef LN2
+# define LN2 0.69314718
+#endif
+
+#ifndef MAX
+# define MAX(a,b) (((a) > (b) ? (a) : (b)))
+#endif
+
+using namespace std;
+namespace Arts {
+
+class Synth_COMPRESSOR_impl : virtual public Synth_COMPRESSOR_skel,
+							  virtual public StdSynthModule
+{
+protected:
+	float _attack, _release, _threshold, _ratiominus1, _output;
+	float _attackfactor, _releasefactor;
+	float _volume;
+	float _compfactor;
+	bool _autooutput;
+
+public:
+	float attack() { return _attack; }
+	float release() { return _release; }
+	float threshold() { return _threshold; }
+	float ratio() { return _ratiominus1 + 1.0; }
+	float output() { return _output; }
+
+	Synth_COMPRESSOR_impl()
+		: _threshold( 1 )
+		, _ratiominus1( -0.2 )
+		, _output( 0 )
+		, _autooutput( true )
+	{
+		newCompFactor();
+		attack( 10 );
+		release( 10 );
+	}
+
+	void newCompFactor()
+	{
+		_compfactor = _output / pow( _threshold, _ratiominus1 );
+	}
+
+	void streamInit()
+	{
+		_volume = 0;
+	}
+
+	void calculateBlock(unsigned long samples)
+	{
+		for( unsigned long i = 0; i < samples; i++ ) {
+			float delta = fabs( invalue[i] ) - _volume;
+			if( delta > 0.0 )
+				_volume += _attackfactor * delta;
+			else
+				_volume += _releasefactor * delta;
+
+			if( _volume > _threshold )
+				// compress
+				// this is what it does:
+				// UtodB(x) = 20 * log( x )
+				// dBtoU(x) = pow( 10, x / 20 )
+				// outvalue[i] = dBtoU( ( UtodB( volume ) - UtodB( threshold ) ) * ratio + UtodB( threshold ) ) / volume * output * invalue[ i ];
+				// showing that it's equal to the formula below
+				// is left as an exercise to the reader.
+				outvalue[i] = pow( _volume, _ratiominus1 ) * _compfactor * invalue[ i ];
+			else
+				outvalue[i] = invalue[i] * _output;
+		}
+	}
+
+	void attack( float newAttack )
+	{ // in ms
+		_attack = newAttack;
+		// _attackfactor has to be <= 1, that's why we need the MAX here
+		_attackfactor = LN2 / MAX( _attack / 1000 * samplingRateFloat, LN2 );
+		attack_changed( newAttack );
+	}
+
+	void release( float newRelease )
+	{ // in ms
+		_release = newRelease;
+		// _releasefactor has to be <= 1, that's why we need the MAX here
+		_releasefactor = LN2 / MAX( _release / 1000 * samplingRateFloat, LN2 );
+		release_changed( newRelease );
+	}
+
+	void threshold( float newThreshold )
+	{ // in V not in dB
+		_threshold = newThreshold;
+		newCompFactor();
+		threshold_changed( newThreshold );
+	}
+
+	void ratio( float newRatio )
+	{
+		_ratiominus1 = newRatio - 1;
+		newCompFactor();
+		ratio_changed( newRatio );
+	}
+
+	void output( float newOutput )
+	{ // in V not in dB
+		_output = newOutput;
+		newCompFactor();
+		output_changed( newOutput );
+	}
+};
+
+REGISTER_IMPLEMENTATION(Synth_COMPRESSOR_impl);
+}