--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/noise.c	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,108 @@
+/*
+ * 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 ------------------------------------------------------------*/