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Diffstat (limited to 'pd/portaudio/pa_common/pa_dither.h')
| -rw-r--r-- | pd/portaudio/pa_common/pa_dither.h | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/pd/portaudio/pa_common/pa_dither.h b/pd/portaudio/pa_common/pa_dither.h new file mode 100644 index 00000000..97116f0f --- /dev/null +++ b/pd/portaudio/pa_common/pa_dither.h @@ -0,0 +1,189 @@ +#ifndef PA_DITHER_H +#define PA_DITHER_H +/* + * $Id: pa_dither.h,v 1.1.2.2 2002/06/05 22:37:03 rossb 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. + */ + +#ifdef __cplusplus +extern "C" +{ +#endif /* __cplusplus */ + + +typedef struct PaUtilTriangularDitherGenerator{ + unsigned long previous; + unsigned long randSeed1; + unsigned long randSeed2; +} PaUtilTriangularDitherGenerator; +/**< State needed to generate a dither signal */ + + +void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *ditherState ); +/**< Initialize dither state */ + +signed long PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *ditherState ); +/**< + Calculate 2 LSB dither signal with a triangular distribution. + Ranged for adding to a 1 bit right-shifted 32 bit integer + prior to >>15. eg: +<pre> + signed long in = * + signed long dither = PaUtil_Generate16BitTriangularDither( ditherState ); + signed short out = (signed short)(((in>>1) + dither) >> 15); +</pre> + @return + A signed long with a range of +32767 to -32768 +*/ + + +float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *ditherState ); +/**< + Calculate 2 LSB dither signal with a triangular distribution. + Ranged for adding to a pre-scaled float. +<pre> + float in = * + float dither = PaUtil_GenerateFloatTriangularDither( ditherState ); + // use smaller scaler to prevent overflow when we add the dither + signed short out = (signed short)(in*(32766.0f) + dither ); +</pre> + @return + A float with a range of -2.0 to +1.99999. +*/ + + + +/* +The following alternate dither algorithms are known... +*/ + +/*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; +} +*/ + +#ifdef __cplusplus +} +#endif /* __cplusplus */ +#endif /* PA_DITHER_H */ |