mirror of
https://github.com/alsa-project/alsa-utils
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96 lines
2.8 KiB
C
96 lines
2.8 KiB
C
/*
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patest_pink.c
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generate Pink Noise using Gardner method.
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Optimization suggested by James McCartney uses a tree
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to select which random value to replace.
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x x x x x x x x x x x x x x x x
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x x x x x x x x
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x x x x
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x x
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x
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Tree is generated by counting trailing zeros in an increasing index.
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When the index is zero, no random number is selected.
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This program uses the Portable Audio library which is under development.
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For more information see: http://www.audiomulch.com/portaudio/
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Author: Phil Burk, http://www.softsynth.com
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Revision History:
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Copyleft 1999 Phil Burk - No rights reserved.
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*/
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#include <stdio.h>
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#include <math.h>
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#include "pink.h"
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/************************************************************/
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/* Calculate pseudo-random 32 bit number based on linear congruential method. */
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static unsigned long generate_random_number( void )
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{
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static unsigned long rand_seed = 22222; /* Change this for different random sequences. */
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rand_seed = (rand_seed * 196314165) + 907633515;
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return rand_seed;
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}
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/* Setup PinkNoise structure for N rows of generators. */
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void initialize_pink_noise( pink_noise_t *pink, int num_rows )
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{
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int i;
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long pmax;
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pink->pink_index = 0;
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pink->pink_index_mask = (1<<num_rows) - 1;
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/* Calculate maximum possible signed random value. Extra 1 for white noise always added. */
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pmax = (num_rows + 1) * (1<<(PINK_RANDOM_BITS-1));
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pink->pink_scalar = 1.0f / pmax;
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/* Initialize rows. */
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for( i=0; i<num_rows; i++ ) pink->pink_rows[i] = 0;
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pink->pink_running_sum = 0;
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}
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/* generate Pink noise values between -1.0 and +1.0 */
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float generate_pink_noise_sample( pink_noise_t *pink )
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{
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long new_random;
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long sum;
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float output;
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/* Increment and mask index. */
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pink->pink_index = (pink->pink_index + 1) & pink->pink_index_mask;
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/* If index is zero, don't update any random values. */
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if( pink->pink_index != 0 )
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{
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/* Determine how many trailing zeros in PinkIndex. */
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/* This algorithm will hang if n==0 so test first. */
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int num_zeros = 0;
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int n = pink->pink_index;
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while( (n & 1) == 0 )
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{
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n = n >> 1;
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num_zeros++;
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}
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/* Replace the indexed ROWS random value.
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* Subtract and add back to Running_sum instead of adding all the random
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* values together. Only one changes each time.
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*/
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pink->pink_running_sum -= pink->pink_rows[num_zeros];
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new_random = ((long)generate_random_number()) >> PINK_RANDOM_SHIFT;
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pink->pink_running_sum += new_random;
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pink->pink_rows[num_zeros] = new_random;
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}
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/* Add extra white noise value. */
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new_random = ((long)generate_random_number()) >> PINK_RANDOM_SHIFT;
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sum = pink->pink_running_sum + new_random;
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/* Scale to range of -1.0 to 0.9999. */
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output = pink->pink_scalar * sum;
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return output;
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}
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