diff options
Diffstat (limited to 'pjmedia/src/pjmedia/portaudio/pa_dither.c')
-rw-r--r-- | pjmedia/src/pjmedia/portaudio/pa_dither.c | 408 |
1 files changed, 204 insertions, 204 deletions
diff --git a/pjmedia/src/pjmedia/portaudio/pa_dither.c b/pjmedia/src/pjmedia/portaudio/pa_dither.c index 5181a8b9..0600db62 100644 --- a/pjmedia/src/pjmedia/portaudio/pa_dither.c +++ b/pjmedia/src/pjmedia/portaudio/pa_dither.c @@ -1,204 +1,204 @@ -/*
- * $Id: pa_dither.c,v 1.1.2.6 2005/05/28 22:49:02 rossbencina Exp $
- * Portable Audio I/O Library triangular dither generator
- *
- * Based on the Open Source API proposed by Ross Bencina
- * Copyright (c) 1999-2002 Phil Burk, Ross Bencina
- *
- * Permission is hereby granted, free of charge, to any person obtaining
- * a copy of this software and associated documentation files
- * (the "Software"), to deal in the Software without restriction,
- * including without limitation the rights to use, copy, modify, merge,
- * publish, distribute, sublicense, and/or sell copies of the Software,
- * and to permit persons to whom the Software is furnished to do so,
- * subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be
- * included in all copies or substantial portions of the Software.
- *
- * Any person wishing to distribute modifications to the Software is
- * requested to send the modifications to the original developer so that
- * they can be incorporated into the canonical version.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
- * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
- * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
- * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
- * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
- * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
- * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-/** @file
- @brief Functions for generating dither noise
-*/
-
-
-#include "pa_dither.h"
-#include "pa_types.h"
-
-#define PA_DITHER_BITS_ (15)
-
-
-void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *state )
-{
- state->previous = 0;
- state->randSeed1 = 22222;
- state->randSeed2 = 5555555;
-}
-
-
-signed long PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *state )
-{
- signed long current, highPass;
-
- /* Generate two random numbers. */
- state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
- state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
-
- /* Generate triangular distribution about 0.
- * Shift before adding to prevent overflow which would skew the distribution.
- * Also shift an extra bit for the high pass filter.
- */
-#define DITHER_SHIFT_ ((SIZEOF_LONG*8 - PA_DITHER_BITS_) + 1)
- current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
- (((signed long)state->randSeed2)>>DITHER_SHIFT_);
-
- /* High pass filter to reduce audibility. */
- highPass = current - state->previous;
- state->previous = current;
- return highPass;
-}
-
-
-/* Multiply by PA_FLOAT_DITHER_SCALE_ to get a float between -2.0 and +1.99999 */
-#define PA_FLOAT_DITHER_SCALE_ (1.0f / ((1<<PA_DITHER_BITS_)-1))
-static const float const_float_dither_scale_ = PA_FLOAT_DITHER_SCALE_;
-
-float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *state )
-{
- signed long current, highPass;
-
- /* Generate two random numbers. */
- state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
- state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
-
- /* Generate triangular distribution about 0.
- * Shift before adding to prevent overflow which would skew the distribution.
- * Also shift an extra bit for the high pass filter.
- */
-#define DITHER_SHIFT_ ((SIZEOF_LONG*8 - PA_DITHER_BITS_) + 1)
- current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
- (((signed long)state->randSeed2)>>DITHER_SHIFT_);
-
- /* High pass filter to reduce audibility. */
- highPass = current - state->previous;
- state->previous = current;
- return ((float)highPass) * const_float_dither_scale_;
-}
-
-
-/*
-The following alternate dither algorithms (from musicdsp.org) could be
-considered
-*/
-
-/*Noise shaped dither (March 2000)
--------------------
-
-This is a simple implementation of highpass triangular-PDF dither with
-2nd-order noise shaping, for use when truncating floating point audio
-data to fixed point.
-
-The noise shaping lowers the noise floor by 11dB below 5kHz (@ 44100Hz
-sample rate) compared to triangular-PDF dither. The code below assumes
-input data is in the range +1 to -1 and doesn't check for overloads!
-
-To save time when generating dither for multiple channels you can do
-things like this: r3=(r1 & 0x7F)<<8; instead of calling rand() again.
-
-
-
- int r1, r2; //rectangular-PDF random numbers
- float s1, s2; //error feedback buffers
- float s = 0.5f; //set to 0.0f for no noise shaping
- float w = pow(2.0,bits-1); //word length (usually bits=16)
- float wi= 1.0f/w;
- float d = wi / RAND_MAX; //dither amplitude (2 lsb)
- float o = wi * 0.5f; //remove dc offset
- float in, tmp;
- int out;
-
-
-//for each sample...
-
- r2=r1; //can make HP-TRI dither by
- r1=rand(); //subtracting previous rand()
-
- in += s * (s1 + s1 - s2); //error feedback
- tmp = in + o + d * (float)(r1 - r2); //dc offset and dither
-
- out = (int)(w * tmp); //truncate downwards
- if(tmp<0.0f) out--; //this is faster than floor()
-
- s2 = s1;
- s1 = in - wi * (float)out; //error
-
-
-
---
-paul.kellett@maxim.abel.co.uk
-http://www.maxim.abel.co.uk
-*/
-
-
-/*
-16-to-8-bit first-order dither
-
-Type : First order error feedforward dithering code
-References : Posted by Jon Watte
-
-Notes :
-This is about as simple a dithering algorithm as you can implement, but it's
-likely to sound better than just truncating to N bits.
-
-Note that you might not want to carry forward the full difference for infinity.
-It's probably likely that the worst performance hit comes from the saturation
-conditionals, which can be avoided with appropriate instructions on many DSPs
-and integer SIMD type instructions, or CMOV.
-
-Last, if sound quality is paramount (such as when going from > 16 bits to 16
-bits) you probably want to use a higher-order dither function found elsewhere
-on this site.
-
-
-Code :
-// This code will down-convert and dither a 16-bit signed short
-// mono signal into an 8-bit unsigned char signal, using a first
-// order forward-feeding error term dither.
-
-#define uchar unsigned char
-
-void dither_one_channel_16_to_8( short * input, uchar * output, int count, int * memory )
-{
- int m = *memory;
- while( count-- > 0 ) {
- int i = *input++;
- i += m;
- int j = i + 32768 - 128;
- uchar o;
- if( j < 0 ) {
- o = 0;
- }
- else if( j > 65535 ) {
- o = 255;
- }
- else {
- o = (uchar)((j>>8)&0xff);
- }
- m = ((j-32768+128)-i);
- *output++ = o;
- }
- *memory = m;
-}
-*/
+/* + * $Id: pa_dither.c,v 1.1.2.6 2005/05/28 22:49:02 rossbencina Exp $ + * Portable Audio I/O Library triangular dither generator + * + * Based on the Open Source API proposed by Ross Bencina + * Copyright (c) 1999-2002 Phil Burk, Ross Bencina + * + * Permission is hereby granted, free of charge, to any person obtaining + * a copy of this software and associated documentation files + * (the "Software"), to deal in the Software without restriction, + * including without limitation the rights to use, copy, modify, merge, + * publish, distribute, sublicense, and/or sell copies of the Software, + * and to permit persons to whom the Software is furnished to do so, + * subject to the following conditions: + * + * The above copyright notice and this permission notice shall be + * included in all copies or substantial portions of the Software. + * + * Any person wishing to distribute modifications to the Software is + * requested to send the modifications to the original developer so that + * they can be incorporated into the canonical version. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. + * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR + * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF + * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION + * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. + */ + +/** @file + @brief Functions for generating dither noise +*/ + + +#include "pa_dither.h" +#include "pa_types.h" + +#define PA_DITHER_BITS_ (15) + + +void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *state ) +{ + state->previous = 0; + state->randSeed1 = 22222; + state->randSeed2 = 5555555; +} + + +signed long PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *state ) +{ + signed long current, highPass; + + /* Generate two random numbers. */ + state->randSeed1 = (state->randSeed1 * 196314165) + 907633515; + state->randSeed2 = (state->randSeed2 * 196314165) + 907633515; + + /* Generate triangular distribution about 0. + * Shift before adding to prevent overflow which would skew the distribution. + * Also shift an extra bit for the high pass filter. + */ +#define DITHER_SHIFT_ ((SIZEOF_LONG*8 - PA_DITHER_BITS_) + 1) + current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) + + (((signed long)state->randSeed2)>>DITHER_SHIFT_); + + /* High pass filter to reduce audibility. */ + highPass = current - state->previous; + state->previous = current; + return highPass; +} + + +/* Multiply by PA_FLOAT_DITHER_SCALE_ to get a float between -2.0 and +1.99999 */ +#define PA_FLOAT_DITHER_SCALE_ (1.0f / ((1<<PA_DITHER_BITS_)-1)) +static const float const_float_dither_scale_ = PA_FLOAT_DITHER_SCALE_; + +float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *state ) +{ + signed long current, highPass; + + /* Generate two random numbers. */ + state->randSeed1 = (state->randSeed1 * 196314165) + 907633515; + state->randSeed2 = (state->randSeed2 * 196314165) + 907633515; + + /* Generate triangular distribution about 0. + * Shift before adding to prevent overflow which would skew the distribution. + * Also shift an extra bit for the high pass filter. + */ +#define DITHER_SHIFT_ ((SIZEOF_LONG*8 - PA_DITHER_BITS_) + 1) + current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) + + (((signed long)state->randSeed2)>>DITHER_SHIFT_); + + /* High pass filter to reduce audibility. */ + highPass = current - state->previous; + state->previous = current; + return ((float)highPass) * const_float_dither_scale_; +} + + +/* +The following alternate dither algorithms (from musicdsp.org) could be +considered +*/ + +/*Noise shaped dither (March 2000) +------------------- + +This is a simple implementation of highpass triangular-PDF dither with +2nd-order noise shaping, for use when truncating floating point audio +data to fixed point. + +The noise shaping lowers the noise floor by 11dB below 5kHz (@ 44100Hz +sample rate) compared to triangular-PDF dither. The code below assumes +input data is in the range +1 to -1 and doesn't check for overloads! + +To save time when generating dither for multiple channels you can do +things like this: r3=(r1 & 0x7F)<<8; instead of calling rand() again. + + + + int r1, r2; //rectangular-PDF random numbers + float s1, s2; //error feedback buffers + float s = 0.5f; //set to 0.0f for no noise shaping + float w = pow(2.0,bits-1); //word length (usually bits=16) + float wi= 1.0f/w; + float d = wi / RAND_MAX; //dither amplitude (2 lsb) + float o = wi * 0.5f; //remove dc offset + float in, tmp; + int out; + + +//for each sample... + + r2=r1; //can make HP-TRI dither by + r1=rand(); //subtracting previous rand() + + in += s * (s1 + s1 - s2); //error feedback + tmp = in + o + d * (float)(r1 - r2); //dc offset and dither + + out = (int)(w * tmp); //truncate downwards + if(tmp<0.0f) out--; //this is faster than floor() + + s2 = s1; + s1 = in - wi * (float)out; //error + + + +-- +paul.kellett@maxim.abel.co.uk +http://www.maxim.abel.co.uk +*/ + + +/* +16-to-8-bit first-order dither + +Type : First order error feedforward dithering code +References : Posted by Jon Watte + +Notes : +This is about as simple a dithering algorithm as you can implement, but it's +likely to sound better than just truncating to N bits. + +Note that you might not want to carry forward the full difference for infinity. +It's probably likely that the worst performance hit comes from the saturation +conditionals, which can be avoided with appropriate instructions on many DSPs +and integer SIMD type instructions, or CMOV. + +Last, if sound quality is paramount (such as when going from > 16 bits to 16 +bits) you probably want to use a higher-order dither function found elsewhere +on this site. + + +Code : +// This code will down-convert and dither a 16-bit signed short +// mono signal into an 8-bit unsigned char signal, using a first +// order forward-feeding error term dither. + +#define uchar unsigned char + +void dither_one_channel_16_to_8( short * input, uchar * output, int count, int * memory ) +{ + int m = *memory; + while( count-- > 0 ) { + int i = *input++; + i += m; + int j = i + 32768 - 128; + uchar o; + if( j < 0 ) { + o = 0; + } + else if( j > 65535 ) { + o = 255; + } + else { + o = (uchar)((j>>8)&0xff); + } + m = ((j-32768+128)-i); + *output++ = o; + } + *memory = m; +} +*/ |