107 lines
3.5 KiB
C
107 lines
3.5 KiB
C
#ifndef PA_DITHER_H
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#define PA_DITHER_H
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/*
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* $Id: pa_dither.h 1418 2009-10-12 21:00:53Z philburk $
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* Portable Audio I/O Library triangular dither generator
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*
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* Based on the Open Source API proposed by Ross Bencina
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* Copyright (c) 1999-2002 Phil Burk, Ross Bencina
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files
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* (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge,
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* publish, distribute, sublicense, and/or sell copies of the Software,
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* and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
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* ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
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* CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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/*
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* The text above constitutes the entire PortAudio license; however,
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* the PortAudio community also makes the following non-binding requests:
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*
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* Any person wishing to distribute modifications to the Software is
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* requested to send the modifications to the original developer so that
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* they can be incorporated into the canonical version. It is also
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* requested that these non-binding requests be included along with the
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* license above.
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*/
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/** @file
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@ingroup common_src
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@brief Functions for generating dither noise
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*/
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#include "pa_types.h"
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#ifdef __cplusplus
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extern "C"
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{
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#endif /* __cplusplus */
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/* Note that the linear congruential algorithm requires 32 bit integers
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* because it uses arithmetic overflow. So use PaUint32 instead of
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* unsigned long so it will work on 64 bit systems.
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*/
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/** @brief State needed to generate a dither signal */
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typedef struct PaUtilTriangularDitherGenerator{
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PaUint32 previous;
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PaUint32 randSeed1;
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PaUint32 randSeed2;
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} PaUtilTriangularDitherGenerator;
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/** @brief Initialize dither state */
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void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *ditherState );
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/**
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@brief Calculate 2 LSB dither signal with a triangular distribution.
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Ranged for adding to a 1 bit right-shifted 32 bit integer
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prior to >>15. eg:
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<pre>
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signed long in = *
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signed long dither = PaUtil_Generate16BitTriangularDither( ditherState );
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signed short out = (signed short)(((in>>1) + dither) >> 15);
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</pre>
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@return
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A signed 32-bit integer with a range of +32767 to -32768
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*/
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PaInt32 PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *ditherState );
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/**
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@brief Calculate 2 LSB dither signal with a triangular distribution.
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Ranged for adding to a pre-scaled float.
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<pre>
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float in = *
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float dither = PaUtil_GenerateFloatTriangularDither( ditherState );
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// use smaller scaler to prevent overflow when we add the dither
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signed short out = (signed short)(in*(32766.0f) + dither );
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</pre>
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@return
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A float with a range of -2.0 to +1.99999.
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*/
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float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *ditherState );
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#ifdef __cplusplus
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}
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#endif /* __cplusplus */
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#endif /* PA_DITHER_H */
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