package dsp.gain;
import java.util.concurrent.atomic.AtomicBoolean;
import buffer.DoubleCircularBuffer;
import buffer.FloatCircularBuffer;
/*******************************************************************************
* SDR Trunk
* Copyright (C) 2014 Dennis Sheirer
* Copyright (C) 2011 Alex Csete
* Copyright (C) 2010 Moe Wheatley
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* 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, see <http://www.gnu.org/licenses/>
*
* ---------------------------------------------------
* Ported from Alex Csete's gqrx source code at:
* https://github.com/csete/gqrx/blob/74ba2742c89b0dfb66854fc9f72d19e5c6e355b6/dsp/agc_impl.cpp
*
* This Software is released under the "Simplified BSD License" + + +
* Copyright 2010 Moe Wheatley. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY Moe Wheatley ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL Moe Wheatley OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* The views and conclusions contained in the software and documentation are
* those of the authors and should not be interpreted as representing
* official policies, either expressed or implied, of Moe Wheatley.
******************************************************************************/
public class AutomaticGainControl
{
private static final double SAMPLE_RATE = 48000;
/* Signal delay line - time delay in seconds */
// private static final double DELAY_TIME_CONSTANT = 0.015;
private static final double DELAY_TIME_CONSTANT = 0.01;
/* Peak detector window - time delay in seconds */
private static final double WINDOW_TIME_CONSTANT = 0.018;
/* Attack time constants in seconds */
private static final double ATTACK_RISE_TIME_CONSTANT = 0.002;
private static final double ATTACK_FALL_TIME_CONSTANT = 0.005;
private static final double ATTACK_RISE_ALPHA = 1.0 -
Math.exp( -1.0 / SAMPLE_RATE * ATTACK_RISE_TIME_CONSTANT );
private static final double ATTACK_FALL_ALPHA = 1.0 -
Math.exp( -1.0 / SAMPLE_RATE * ATTACK_FALL_TIME_CONSTANT );
/* AGC decay value in milliseconds (20 to 5000) */
private static final double DECAY = 200;
/* Ratio between rise and fall times of decay time constants - adjust for
* best action with SSB */
private static final double DECAY_RISEFALL_RATIO = 0.3;
private static final double DECAY_RISE_ALPHA = 1.0 -
Math.exp( -1.0 / ( SAMPLE_RATE * DECAY * .001 * DECAY_RISEFALL_RATIO ) );
private static final double DECAY_FALL_ALPHA = 1.0 -
Math.exp( -1.0 / ( SAMPLE_RATE * DECAY * .001 ) );
/* Hang timer release decay time constant in seconds */
@SuppressWarnings( "unused" )
private static final double RELEASE_TIME_CONSTANT = 0.05;
/* Specifies the AGC Knee in dB if AGC is active (nominal range -160 to 0 dB) */
private static final double THRESHOLD = -100;
/* Limit output to about 3db of maximum */
private static final double AGC_OUT_SCALE = 0.7;
/* Keep max input and output the same */
private static final double MAX_AMPLITUDE = 32767.0; //1.0;
private static final double MAX_MANUAL_AMPLITUDE = 32767.0; //1.0;
/* Specifies AGC manual gain in dB if AGC is not active ( 0 to 100 dB) */
private static final double MANUAL_GAIN = 0.0;
private static final double MANUAL_AGC_GAIN = MAX_MANUAL_AMPLITUDE *
Math.pow( 10.0, MANUAL_GAIN / 20.0 );
/* Specifies dB reduction in output at knee from max output level (0 - 10dB) */
private static final double SLOPE_FACTOR = 2.0;
private static final double KNEE = THRESHOLD / 20.0;
private static final double GAIN_SLOPE = SLOPE_FACTOR / 100.0;
private static final double FIXED_GAIN = AGC_OUT_SCALE *
Math.pow( 10.0, KNEE * ( GAIN_SLOPE - 1.0 ) );
/* Constant for calc log() so that a value of 0 magnitude = -8 */
private static final double MIN_CONSTANT = 3.2767E-4;
private AtomicBoolean mAGCEnabled = new AtomicBoolean( true );
private double mPeakMagnitude = 0.0;
private double mAttackAverage = 0.0;
private double mDecayAverage = 0.0;
private FloatCircularBuffer mDelayBuffer =
new FloatCircularBuffer( (int)( SAMPLE_RATE * DELAY_TIME_CONSTANT ) );
private DoubleCircularBuffer mMagnitudeBuffer =
new DoubleCircularBuffer( (int)( SAMPLE_RATE * WINDOW_TIME_CONSTANT ) );
public AutomaticGainControl()
{
}
public float process( float currentSample )
{
float delayedSample = mDelayBuffer.get( currentSample );
double gain = MANUAL_AGC_GAIN;
if( mAGCEnabled.get() )
{
double currentMagnitude = Math.log10( Math.abs( currentSample ) +
MIN_CONSTANT ) - Math.log10( MAX_AMPLITUDE );
double delayedMagnitude = mMagnitudeBuffer.get( currentMagnitude );
if( currentMagnitude > mPeakMagnitude )
{
/* Use current magnitude as peak if it's larger */
mPeakMagnitude = currentMagnitude;
}
else if( delayedMagnitude == mPeakMagnitude )
{
/* If delayed magnitude is the current peak, then find a new peak */
mPeakMagnitude = mMagnitudeBuffer.max();
}
/* Exponential decay mode */
if( mPeakMagnitude > mAttackAverage )
{
mAttackAverage = ( ( 1.0 - ATTACK_RISE_ALPHA ) * mAttackAverage ) +
( ATTACK_RISE_ALPHA * mPeakMagnitude );
}
else
{
mAttackAverage = ( ( 1.0 - ATTACK_FALL_ALPHA ) * mAttackAverage ) +
( ATTACK_FALL_ALPHA * mPeakMagnitude );
}
if( mPeakMagnitude > mDecayAverage )
{
mDecayAverage = ( ( 1.0 - DECAY_RISE_ALPHA ) * mDecayAverage ) +
( DECAY_RISE_ALPHA * mPeakMagnitude );
}
else
{
mDecayAverage = ( ( 1.0 - DECAY_FALL_ALPHA ) * mDecayAverage ) +
( DECAY_RISE_ALPHA * mPeakMagnitude );
}
double magnitude = ( mAttackAverage > mDecayAverage ) ?
mAttackAverage : mDecayAverage;
if( magnitude < KNEE )
{
gain = FIXED_GAIN;
}
else
{
gain = AGC_OUT_SCALE * Math.pow( 10.0,
magnitude * ( GAIN_SLOPE - 1.0 ) );
}
}
return (float)( delayedSample * gain );
}
/**
* Enables or disables Automatic Gain Control (AGC).
*/
public void setAGCEnabled( boolean enabled )
{
mAGCEnabled.set( enabled );
}
/**
* Indicates if AGC is enabled
* @return true=AGC, false=MANUAL GAIN
*/
public boolean isAGCEnabled()
{
return mAGCEnabled.get();
}
}