130 lines
4.0 KiB
C
130 lines
4.0 KiB
C
/*
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* SpanDSP - a series of DSP components for telephony
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*
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* noise.c - A low complexity audio noise generator, suitable for
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* real time generation (current AWGN, and Hoth)
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*
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* Written by Steve Underwood <steveu@coppice.org>
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*
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* Copyright (C) 2005 Steve Underwood
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*
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* All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License version 2.1,
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*! \file */
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#if defined(HAVE_CONFIG_H)
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#include "config.h"
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#endif
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#include <stdlib.h>
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#include <stdio.h>
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#include <inttypes.h>
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#include <memory.h>
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#if defined(HAVE_TGMATH_H)
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#include <tgmath.h>
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#endif
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#if defined(HAVE_MATH_H)
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#include <math.h>
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#endif
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#include "floating_fudge.h"
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#include "spandsp/telephony.h"
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#include "spandsp/alloc.h"
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#include "spandsp/fast_convert.h"
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#include "spandsp/saturated.h"
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#include "spandsp/noise.h"
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#include "spandsp/private/noise.h"
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SPAN_DECLARE(int16_t) noise(noise_state_t *s)
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{
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int32_t val;
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int i;
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/* The central limit theorem says if you add a few random numbers together,
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the result starts to look Gaussian. Quantities above 7 give diminishing
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returns. Quantites above 20 are exceedingly Gaussian. */
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val = 0;
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for (i = 0; i < s->quality; i++)
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{
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s->rndnum = 1664525U*s->rndnum + 1013904223U;
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val += ((int32_t) s->rndnum) >> 22;
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}
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if (s->class_of_noise == NOISE_CLASS_HOTH)
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{
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/* Hoth noise is room-like. It should be sculpted, at the high and low ends,
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and roll off at 5dB/octave across the main part of the band. However,
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merely rolling off at 6dB/octave across the band gets you close
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to the subjective effect. */
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s->state = (3*val + 5*s->state) >> 3;
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/* Bring the overall power level back to the pre-filtered level. This
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simple approx. leaves the signal about 0.35dB low. */
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val = s->state << 1;
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}
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return saturate16((val*s->rms) >> 10);
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}
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/*- End of function --------------------------------------------------------*/
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SPAN_DECLARE(noise_state_t *) noise_init_dbov(noise_state_t *s, int seed, float level, int class_of_noise, int quality)
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{
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float rms;
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if (s == NULL)
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{
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if ((s = (noise_state_t *) span_alloc(sizeof(*s))) == NULL)
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return NULL;
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}
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memset(s, 0, sizeof(*s));
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s->rndnum = (uint32_t) seed;
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rms = 32768.0f*powf(10.0f, level/20.0f);
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if (quality < 4)
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s->quality = 4;
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else if (quality > 20)
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s->quality = 20;
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else
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s->quality = quality;
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if (class_of_noise == NOISE_CLASS_HOTH)
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{
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/* Allow for the gain of the filter */
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rms *= 1.043f;
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}
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s->rms = (int32_t) (rms*sqrtf(12.0f/s->quality));
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s->class_of_noise = class_of_noise;
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return s;
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}
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/*- End of function --------------------------------------------------------*/
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SPAN_DECLARE(noise_state_t *) noise_init_dbm0(noise_state_t *s, int seed, float level, int class_of_noise, int quality)
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{
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return noise_init_dbov(s, seed, (level - DBM0_MAX_POWER), class_of_noise, quality);
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}
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/*- End of function --------------------------------------------------------*/
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SPAN_DECLARE(int) noise_release(noise_state_t *s)
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{
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return 0;
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}
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/*- End of function --------------------------------------------------------*/
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SPAN_DECLARE(int) noise_free(noise_state_t *s)
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{
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span_free(s);
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return 0;
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}
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/*- End of function --------------------------------------------------------*/
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/*- End of file ------------------------------------------------------------*/
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