/[pcsx2_0.9.7]/trunk/3rdparty/portaudio/src/common/pa_dither.c
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Contents of /trunk/3rdparty/portaudio/src/common/pa_dither.c

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Revision 10 - (show annotations) (download)
Mon Sep 6 11:40:06 2010 UTC (9 years, 11 months ago) by william
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exported r3113 from ./upstream/trunk
1 /*
2 * $Id: pa_dither.c 1418 2009-10-12 21:00:53Z philburk $
3 * Portable Audio I/O Library triangular dither generator
4 *
5 * Based on the Open Source API proposed by Ross Bencina
6 * Copyright (c) 1999-2002 Phil Burk, Ross Bencina
7 *
8 * Permission is hereby granted, free of charge, to any person obtaining
9 * a copy of this software and associated documentation files
10 * (the "Software"), to deal in the Software without restriction,
11 * including without limitation the rights to use, copy, modify, merge,
12 * publish, distribute, sublicense, and/or sell copies of the Software,
13 * and to permit persons to whom the Software is furnished to do so,
14 * subject to the following conditions:
15 *
16 * The above copyright notice and this permission notice shall be
17 * included in all copies or substantial portions of the Software.
18 *
19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
21 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
22 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
23 * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
24 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
25 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
26 */
27
28 /*
29 * The text above constitutes the entire PortAudio license; however,
30 * the PortAudio community also makes the following non-binding requests:
31 *
32 * Any person wishing to distribute modifications to the Software is
33 * requested to send the modifications to the original developer so that
34 * they can be incorporated into the canonical version. It is also
35 * requested that these non-binding requests be included along with the
36 * license above.
37 */
38
39 /** @file
40 @ingroup common_src
41
42 @brief Functions for generating dither noise
43 */
44
45 #include "pa_types.h"
46 #include "pa_dither.h"
47
48
49 /* Note that the linear congruential algorithm requires 32 bit integers
50 * because it uses arithmetic overflow. So use PaUint32 instead of
51 * unsigned long so it will work on 64 bit systems.
52 */
53
54 #define PA_DITHER_BITS_ (15)
55
56
57 void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *state )
58 {
59 state->previous = 0;
60 state->randSeed1 = 22222;
61 state->randSeed2 = 5555555;
62 }
63
64
65 PaInt32 PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *state )
66 {
67 PaInt32 current, highPass;
68
69 /* Generate two random numbers. */
70 state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
71 state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
72
73 /* Generate triangular distribution about 0.
74 * Shift before adding to prevent overflow which would skew the distribution.
75 * Also shift an extra bit for the high pass filter.
76 */
77 #define DITHER_SHIFT_ ((sizeof(PaInt32)*8 - PA_DITHER_BITS_) + 1)
78
79 current = (((PaInt32)state->randSeed1)>>DITHER_SHIFT_) +
80 (((PaInt32)state->randSeed2)>>DITHER_SHIFT_);
81
82 /* High pass filter to reduce audibility. */
83 highPass = current - state->previous;
84 state->previous = current;
85 return highPass;
86 }
87
88
89 /* Multiply by PA_FLOAT_DITHER_SCALE_ to get a float between -2.0 and +1.99999 */
90 #define PA_FLOAT_DITHER_SCALE_ (1.0f / ((1<<PA_DITHER_BITS_)-1))
91 static const float const_float_dither_scale_ = PA_FLOAT_DITHER_SCALE_;
92
93 float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *state )
94 {
95 PaInt32 current, highPass;
96
97 /* Generate two random numbers. */
98 state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
99 state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
100
101 /* Generate triangular distribution about 0.
102 * Shift before adding to prevent overflow which would skew the distribution.
103 * Also shift an extra bit for the high pass filter.
104 */
105 current = (((PaInt32)state->randSeed1)>>DITHER_SHIFT_) +
106 (((PaInt32)state->randSeed2)>>DITHER_SHIFT_);
107
108 /* High pass filter to reduce audibility. */
109 highPass = current - state->previous;
110 state->previous = current;
111 return ((float)highPass) * const_float_dither_scale_;
112 }
113
114
115 /*
116 The following alternate dither algorithms (from musicdsp.org) could be
117 considered
118 */
119
120 /*Noise shaped dither (March 2000)
121 -------------------
122
123 This is a simple implementation of highpass triangular-PDF dither with
124 2nd-order noise shaping, for use when truncating floating point audio
125 data to fixed point.
126
127 The noise shaping lowers the noise floor by 11dB below 5kHz (@ 44100Hz
128 sample rate) compared to triangular-PDF dither. The code below assumes
129 input data is in the range +1 to -1 and doesn't check for overloads!
130
131 To save time when generating dither for multiple channels you can do
132 things like this: r3=(r1 & 0x7F)<<8; instead of calling rand() again.
133
134
135
136 int r1, r2; //rectangular-PDF random numbers
137 float s1, s2; //error feedback buffers
138 float s = 0.5f; //set to 0.0f for no noise shaping
139 float w = pow(2.0,bits-1); //word length (usually bits=16)
140 float wi= 1.0f/w;
141 float d = wi / RAND_MAX; //dither amplitude (2 lsb)
142 float o = wi * 0.5f; //remove dc offset
143 float in, tmp;
144 int out;
145
146
147 //for each sample...
148
149 r2=r1; //can make HP-TRI dither by
150 r1=rand(); //subtracting previous rand()
151
152 in += s * (s1 + s1 - s2); //error feedback
153 tmp = in + o + d * (float)(r1 - r2); //dc offset and dither
154
155 out = (int)(w * tmp); //truncate downwards
156 if(tmp<0.0f) out--; //this is faster than floor()
157
158 s2 = s1;
159 s1 = in - wi * (float)out; //error
160
161
162
163 --
164 paul.kellett@maxim.abel.co.uk
165 http://www.maxim.abel.co.uk
166 */
167
168
169 /*
170 16-to-8-bit first-order dither
171
172 Type : First order error feedforward dithering code
173 References : Posted by Jon Watte
174
175 Notes :
176 This is about as simple a dithering algorithm as you can implement, but it's
177 likely to sound better than just truncating to N bits.
178
179 Note that you might not want to carry forward the full difference for infinity.
180 It's probably likely that the worst performance hit comes from the saturation
181 conditionals, which can be avoided with appropriate instructions on many DSPs
182 and integer SIMD type instructions, or CMOV.
183
184 Last, if sound quality is paramount (such as when going from > 16 bits to 16
185 bits) you probably want to use a higher-order dither function found elsewhere
186 on this site.
187
188
189 Code :
190 // This code will down-convert and dither a 16-bit signed short
191 // mono signal into an 8-bit unsigned char signal, using a first
192 // order forward-feeding error term dither.
193
194 #define uchar unsigned char
195
196 void dither_one_channel_16_to_8( short * input, uchar * output, int count, int * memory )
197 {
198 int m = *memory;
199 while( count-- > 0 ) {
200 int i = *input++;
201 i += m;
202 int j = i + 32768 - 128;
203 uchar o;
204 if( j < 0 ) {
205 o = 0;
206 }
207 else if( j > 65535 ) {
208 o = 255;
209 }
210 else {
211 o = (uchar)((j>>8)&0xff);
212 }
213 m = ((j-32768+128)-i);
214 *output++ = o;
215 }
216 *memory = m;
217 }
218 */

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