sdrangel/sdrbase/dsp/fmpreemphasis.h

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///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2020 Jon Beniston, M7RCE //
// //
// 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 as version 3 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 V3 for more details. //
// //
// You should have received a copy of the GNU General Public License //
// along with this program. If not, see <http://www.gnu.org/licenses/>. //
///////////////////////////////////////////////////////////////////////////////////
#ifndef INCLUDE_DSP_FMPREEMPHASIS_H_
#define INCLUDE_DSP_FMPREEMPHASIS_H_
#include "dsp/dsptypes.h"
#include "export.h"
#define FMPREEMPHASIS_TAU_EU 50e-6f
#define FMPREEMPHASIS_TAU_US 75e-6f
/** FM preemphasis filter.
* Amplifies frequencies above ~3.2k (tau=50e-6 in EU) or ~2.1k (tau=75e-6 in US)
* at ~6dB per octave, and then flattens at 12k (highFreq).
* Frequency response:
* highFreq
* -------
* /
* /
* -------/
* 1/(2*pi*tau)
*/
class SDRBASE_API FMPreemphasis
{
public:
FMPreemphasis(int sampleRate, Real tau = FMPREEMPHASIS_TAU_EU, Real highFreq = 12000.0);
void configure(int sampleRate, Real tau = FMPREEMPHASIS_TAU_EU, Real highFreq = 12000.0);
Real filter(Real sampleIn);
private:
Real m_z; // Delay element
Real m_b0; // IIR numerator taps
Real m_b1;
Real m_a1; // IIR denominator taps
};
#endif /* INCLUDE_DSP_FMPREEMPHASIS_H_ */