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Equalizer.java

/*
 * 11/19/04       1.0 moved to LGPL.
 * 12/12/99       Initial version.  mdm@techie.com
 *-----------------------------------------------------------------------
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library General Public License as published
 *   by the Free Software Foundation; either version 2 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 Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this program; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *----------------------------------------------------------------------
 */


package javazoom.jl.decoder;

/**
 * The <code>Equalizer</code> class can be used to specify
 * equalization settings for the MPEG audio decoder. 
 * <p>
 * The equalizer consists of 32 band-pass filters. 
 * Each band of the equalizer can take on a fractional value between 
 * -1.0 and +1.0.
 * At -1.0, the input signal is attenuated by 6dB, at +1.0 the signal is
 * amplified by 6dB. 
 * 
 * @see Decoder
 * 
 * @author MDM
 */
00038 public final class Equalizer
{           
      /**
       * Equalizer setting to denote that a given band will not be
       * present in the output signal.
       */
00044       static public final float BAND_NOT_PRESENT = Float.NEGATIVE_INFINITY;
            
      static public final Equalizer PASS_THRU_EQ = new Equalizer();
      
      private static final int BANDS = 32;
      
      private final float[]   settings = new float[BANDS];
      
      /**
       * Creates a new <code>Equalizer</code> instance. 
       */
00055       public Equalizer()
      {           
      }
      
//    private Equalizer(float b1, float b2, float b3, float b4, float b5,
//                             float b6, float b7, float b8, float b9, float b10, float b11,
//                             float b12, float b13, float b14, float b15, float b16,
//                             float b17, float b18, float b19, float b20);

      public Equalizer(float[] settings)
      {
            setFrom(settings);
      }
      
      public Equalizer(EQFunction eq)
      {
            setFrom(eq);
      }
      
      public void setFrom(float[] eq)
      {
            reset();
            int max = (eq.length > BANDS) ? BANDS : eq.length;
            
            for (int i=0; i<max; i++)
            {
                  settings[i] = limit(eq[i]);
            }
      }

      public void setFrom(EQFunction eq)
      {
            reset();
            int max = BANDS;
            
            for (int i=0; i<max; i++)
            {
                  settings[i] = limit(eq.getBand(i));
            }           
      }
      
      /**
       * Sets the bands of this equalizer to the value the bands of
       * another equalizer. Bands that are not present in both equalizers are ignored. 
       */
00100       public void setFrom(Equalizer eq)
      {
            if (eq!=this)
            {
                  setFrom(eq.settings);
            }
      }
      
      
      
      
      /**
       * Sets all bands to 0.0
       */
00114       public void reset()
      {
            for (int i=0; i<BANDS; i++)
            {
                  settings[i] = 0.0f;
            }
      }

      
      /**
       * Retrieves the number of bands present in this equalizer.
       */
00126       public int getBandCount()
      {
            return settings.length; 
      }
      
      public float setBand(int band, float neweq)
      {
            float eq = 0.0f;
            
            if ((band>=0) && (band<BANDS))
            {
                  eq = settings[band];
                  settings[band] = limit(neweq);
            }
            
            return eq;        
      }
      
      
      
      /**
       * Retrieves the eq setting for a given band.
       */
00149       public float getBand(int band)
      {
            float eq = 0.0f;
            
            if ((band>=0) && (band<BANDS))
            {
                  eq = settings[band];
            }
            
            return eq;
      }
      
      private float limit(float eq)
      {
            if (eq==BAND_NOT_PRESENT)
                  return eq;
            if (eq > 1.0f)
                  return 1.0f;
            if (eq < -1.0f)
                  return -1.0f;
            
            return eq;
      }
      
      /**
       * Retrieves an array of floats whose values represent a
       * scaling factor that can be applied to linear samples
       * in each band to provide the equalization represented by
       * this instance. 
       * 
       * @return  an array of factors that can be applied to the
       *                subbands.
       */
00182       float[] getBandFactors()
      {
            float[] factors = new float[BANDS];
            for (int i=0, maxCount=BANDS; i<maxCount; i++)
            {
                  factors[i] = getBandFactor(settings[i]);
            }
            
            return factors;
      }
      
      /**
       * Converts an equalizer band setting to a sample factor.
       * The factor is determined by the function f = 2^n where
       * n is the equalizer band setting in the range [-1.0,1.0].
       *     
       */
00199       float getBandFactor(float eq)
      {
            if (eq==BAND_NOT_PRESENT)
                  return 0.0f;
            
            float f = (float)Math.pow(2.0, eq);
            return f;
      }
      
      
      static abstract public class EQFunction
      {
            /**
             * Returns the setting of a band in the equalizer. 
             * 
             * @param band    The index of the band to retrieve the setting
             *                      for. 
             * 
             * @return        the setting of the specified band. This is a value between
             *                      -1 and +1.
             */
            public float getBand(int band)
            {
                  return 0.0f;      
            }
            
      }
            
}

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