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56 lines
2.3 KiB
C
56 lines
2.3 KiB
C
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///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2020 Jon Beniston, M7RCE //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// (at your option) any later version. //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#ifndef INCLUDE_DSP_FMPREEMPHASIS_H_
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#define INCLUDE_DSP_FMPREEMPHASIS_H_
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#include "dsp/dsptypes.h"
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#include "export.h"
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#define FMPREEMPHASIS_TAU_EU 50e-6f
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#define FMPREEMPHASIS_TAU_US 75e-6f
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/** FM preemphasis filter.
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* Amplifies frequencies above ~3.2k (tau=50e-6 in EU) or ~2.1k (tau=75e-6 in US)
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* at ~6dB per octave, and then flattens at 12k (highFreq).
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* Frequency response:
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* highFreq
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* -------
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* /
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* /
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* -------/
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* 1/(2*pi*tau)
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*/
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class SDRBASE_API FMPreemphasis
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{
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public:
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FMPreemphasis(int sampleRate, Real tau = FMPREEMPHASIS_TAU_EU, Real highFreq = 12000.0);
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void configure(int sampleRate, Real tau = FMPREEMPHASIS_TAU_EU, Real highFreq = 12000.0);
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Real filter(Real sampleIn);
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private:
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Real m_z; // Delay element
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Real m_b0; // IIR numerator taps
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Real m_b1;
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Real m_a1; // IIR denominator taps
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};
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#endif /* INCLUDE_DSP_FMPREEMPHASIS_H_ */
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