moved trunk into place
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bjornroche
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src/common/pa_dither.c
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src/common/pa_dither.c
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/*
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* $Id$
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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_dither.h"
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#include "pa_types.h"
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#define PA_DITHER_BITS_ (15)
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void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *state )
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{
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state->previous = 0;
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state->randSeed1 = 22222;
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state->randSeed2 = 5555555;
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}
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signed long PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *state )
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{
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signed long current, highPass;
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/* Generate two random numbers. */
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state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
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state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
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/* Generate triangular distribution about 0.
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* Shift before adding to prevent overflow which would skew the distribution.
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* Also shift an extra bit for the high pass filter.
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*/
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#define DITHER_SHIFT_ ((SIZEOF_LONG*8 - PA_DITHER_BITS_) + 1)
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current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
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(((signed long)state->randSeed2)>>DITHER_SHIFT_);
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/* High pass filter to reduce audibility. */
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highPass = current - state->previous;
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state->previous = current;
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return highPass;
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}
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/* Multiply by PA_FLOAT_DITHER_SCALE_ to get a float between -2.0 and +1.99999 */
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#define PA_FLOAT_DITHER_SCALE_ (1.0f / ((1<<PA_DITHER_BITS_)-1))
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static const float const_float_dither_scale_ = PA_FLOAT_DITHER_SCALE_;
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float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *state )
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{
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signed long current, highPass;
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/* Generate two random numbers. */
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state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
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state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
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/* Generate triangular distribution about 0.
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* Shift before adding to prevent overflow which would skew the distribution.
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* Also shift an extra bit for the high pass filter.
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*/
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#define DITHER_SHIFT_ ((SIZEOF_LONG*8 - PA_DITHER_BITS_) + 1)
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current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
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(((signed long)state->randSeed2)>>DITHER_SHIFT_);
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/* High pass filter to reduce audibility. */
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highPass = current - state->previous;
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state->previous = current;
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return ((float)highPass) * const_float_dither_scale_;
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}
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/*
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The following alternate dither algorithms (from musicdsp.org) could be
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considered
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*/
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/*Noise shaped dither (March 2000)
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-------------------
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This is a simple implementation of highpass triangular-PDF dither with
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2nd-order noise shaping, for use when truncating floating point audio
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data to fixed point.
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The noise shaping lowers the noise floor by 11dB below 5kHz (@ 44100Hz
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sample rate) compared to triangular-PDF dither. The code below assumes
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input data is in the range +1 to -1 and doesn't check for overloads!
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To save time when generating dither for multiple channels you can do
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things like this: r3=(r1 & 0x7F)<<8; instead of calling rand() again.
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int r1, r2; //rectangular-PDF random numbers
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float s1, s2; //error feedback buffers
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float s = 0.5f; //set to 0.0f for no noise shaping
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float w = pow(2.0,bits-1); //word length (usually bits=16)
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float wi= 1.0f/w;
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float d = wi / RAND_MAX; //dither amplitude (2 lsb)
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float o = wi * 0.5f; //remove dc offset
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float in, tmp;
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int out;
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//for each sample...
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r2=r1; //can make HP-TRI dither by
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r1=rand(); //subtracting previous rand()
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in += s * (s1 + s1 - s2); //error feedback
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tmp = in + o + d * (float)(r1 - r2); //dc offset and dither
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out = (int)(w * tmp); //truncate downwards
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if(tmp<0.0f) out--; //this is faster than floor()
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s2 = s1;
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s1 = in - wi * (float)out; //error
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--
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paul.kellett@maxim.abel.co.uk
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http://www.maxim.abel.co.uk
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*/
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/*
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16-to-8-bit first-order dither
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Type : First order error feedforward dithering code
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References : Posted by Jon Watte
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Notes :
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This is about as simple a dithering algorithm as you can implement, but it's
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likely to sound better than just truncating to N bits.
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Note that you might not want to carry forward the full difference for infinity.
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It's probably likely that the worst performance hit comes from the saturation
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conditionals, which can be avoided with appropriate instructions on many DSPs
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and integer SIMD type instructions, or CMOV.
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Last, if sound quality is paramount (such as when going from > 16 bits to 16
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bits) you probably want to use a higher-order dither function found elsewhere
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on this site.
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Code :
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// This code will down-convert and dither a 16-bit signed short
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// mono signal into an 8-bit unsigned char signal, using a first
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// order forward-feeding error term dither.
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#define uchar unsigned char
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void dither_one_channel_16_to_8( short * input, uchar * output, int count, int * memory )
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{
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int m = *memory;
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while( count-- > 0 ) {
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int i = *input++;
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i += m;
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int j = i + 32768 - 128;
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uchar o;
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if( j < 0 ) {
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o = 0;
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}
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else if( j > 65535 ) {
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o = 255;
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}
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else {
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o = (uchar)((j>>8)&0xff);
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}
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m = ((j-32768+128)-i);
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*output++ = o;
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}
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*memory = m;
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}
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*/
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