2023-11-18 06:36:53 +01:00
|
|
|
///////////////////////////////////////////////////////////////////////////////////////
|
|
|
|
|
// Copyright (C) 2022 Edouard Griffiths, F4EXB <f4exb06@gmail.com> //
|
|
|
|
|
// //
|
|
|
|
|
// 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/>. //
|
|
|
|
|
///////////////////////////////////////////////////////////////////////////////////////
|
2022-06-29 08:45:44 +02:00
|
|
|
// Polyphase decimation filter.
|
|
|
|
|
//
|
|
|
|
|
// Convert an oversampled audio stream to non-oversampled. Uses a
|
|
|
|
|
// windowed sinc FIR filter w/ Blackman window to control aliasing.
|
|
|
|
|
// Christian Floisand's 'blog explains it very well.
|
|
|
|
|
//
|
|
|
|
|
// This version has a very simple main processing loop (the decimate
|
|
|
|
|
// method) which vectorizes easily.
|
|
|
|
|
//
|
|
|
|
|
// Refs:
|
|
|
|
|
// https://christianfloisand.wordpress.com/2012/12/05/audio-resampling-part-1/
|
|
|
|
|
// https://christianfloisand.wordpress.com/2013/01/28/audio-resampling-part-2/
|
|
|
|
|
// http://www.dspguide.com/ch16.htm
|
|
|
|
|
// http://en.wikipedia.org/wiki/Window_function#Blackman_windows
|
|
|
|
|
|
|
|
|
|
#ifndef INCLUDE_M17MODDECIMATOR_H
|
|
|
|
|
#define INCLUDE_M17MODDECIMATOR_H
|
|
|
|
|
|
|
|
|
|
#include <cstdint>
|
|
|
|
|
|
|
|
|
|
class M17ModDecimator {
|
|
|
|
|
|
|
|
|
|
public:
|
|
|
|
|
M17ModDecimator();
|
|
|
|
|
~M17ModDecimator();
|
|
|
|
|
|
|
|
|
|
void initialize(
|
|
|
|
|
double decimatedSampleRate,
|
|
|
|
|
double passFrequency,
|
|
|
|
|
unsigned oversampleRatio
|
|
|
|
|
);
|
|
|
|
|
|
|
|
|
|
double oversampleRate() const { return mOversampleRate; }
|
|
|
|
|
int oversampleRatio() const { return mRatio; }
|
|
|
|
|
|
|
|
|
|
void decimate(int16_t *in, int16_t *out, unsigned int outCount);
|
|
|
|
|
// N.B., input must have (ratio * outCount) samples.
|
|
|
|
|
|
|
|
|
|
private:
|
|
|
|
|
double mDecimatedSampleRate;
|
|
|
|
|
double mOversampleRate;
|
|
|
|
|
int mRatio; // oversample ratio
|
|
|
|
|
float *mKernel;
|
|
|
|
|
unsigned int mKernelSize;
|
|
|
|
|
float *mShift; // shift register
|
|
|
|
|
unsigned int mCursor;
|
|
|
|
|
};
|
|
|
|
|
|
|
|
|
|
#endif // INCLUDE_M17MODDECIMATOR_H
|
