Mercurial > hg > audiostuff
view spandsp-0.0.3/spandsp-0.0.3/src/noise.c @ 5:f762bf195c4b
import spandsp-0.0.3
author | Peter Meerwald <pmeerw@cosy.sbg.ac.at> |
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date | Fri, 25 Jun 2010 16:00:21 +0200 |
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/* * SpanDSP - a series of DSP components for telephony * * noise.c - A low complexity audio noise generator, suitable for * real time generation (current AWGN, and Hoth) * * Written by Steve Underwood <steveu@coppice.org> * * Copyright (C) 2005 Steve Underwood * * All rights reserved. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2, as * published by the Free Software Foundation. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. * * $Id: noise.c,v 1.17 2006/11/28 16:59:56 steveu Exp $ */ /*! \file */ #ifdef HAVE_CONFIG_H #include <config.h> #endif #include <stdlib.h> #include <stdio.h> #include <inttypes.h> #include <memory.h> #if defined(HAVE_TGMATH_H) #include <tgmath.h> #endif #if defined(HAVE_MATH_H) #include <math.h> #endif #include "spandsp/telephony.h" #include "spandsp/dc_restore.h" #include "spandsp/noise.h" int16_t noise(noise_state_t *s) { int32_t val; int i; /* The central limit theorem says if you add a few random numbers together, the result starts to look Gaussian. Quantities above 7 give diminishing returns. Quantites above 20 are exceedingly Gaussian. */ val = 0; for (i = 0; i < s->quality; i++) { s->rndnum = 1664525U*s->rndnum + 1013904223U; val += ((int32_t) s->rndnum) >> 22; } if (s->class_of_noise == NOISE_CLASS_HOTH) { /* Hoth noise is room-like. It should be sculpted, at the high and low ends, and roll off at 5dB/octave across the main part of the band. However, merely rolling off at 6dB/octave across the band gets you close to the subjective effect. */ s->state = (3*val + 5*s->state) >> 3; /* Bring the overall power level back to the pre-filtered level. This simple approx. leaves the signal about 0.35dB low. */ val = s->state << 1; } return saturate((val*s->rms) >> 10); } /*- End of function --------------------------------------------------------*/ noise_state_t *noise_init_dbm0(noise_state_t *s, int seed, float level, int class_of_noise, int quality) { return noise_init_dbov(s, seed, (level - DBM0_MAX_POWER), class_of_noise, quality); } /*- End of function --------------------------------------------------------*/ noise_state_t *noise_init_dbov(noise_state_t *s, int seed, float level, int class_of_noise, int quality) { float rms; memset(s, 0, sizeof(*s)); s->rndnum = (uint32_t) seed; rms = 32768.0f*powf(10.0f, level/20.0f); if (quality < 4) s->quality = 4; else if (quality > 20) s->quality = 20; else s->quality = quality; if (class_of_noise == NOISE_CLASS_HOTH) { /* Allow for the gain of the filter */ rms *= 1.043f; } s->rms = (int32_t) (rms*sqrt(12.0/quality)); s->class_of_noise = class_of_noise; return s; } /*- End of function --------------------------------------------------------*/ /*- End of file ------------------------------------------------------------*/