equalizer.java

java处理声音文件

/*
 * 12/12/99		Initial version.	[e-mail]
/*-----------------------------------------------------------------------
 *  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 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 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.
 *----------------------------------------------------------------------
 */


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
 */

public final class Equalizer
{		
	/**
	 * Equalizer setting to denote that a given band will not be
	 * present in the output signal.
	 */
	static public final float BAND_NOT_PRESENT = Float.NEGATIVE_INFINITY;
	
	static public final EQFunction PASS_THRU = new EQFunction();
	
	
	private static final int BANDS = 32;
	
	private final float[]	settings = new float[BANDS];
	
	/**
	 * Creates a new <code>Equalizer</code> instance. 
	 */
	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. 
	 */
	public void setFrom(Equalizer eq)
	{
		setFrom(eq.settings);
	}
	
	
	
	
	/**
	 * Sets all bands to 0.0
	 */
	public void reset()
	{
		for (int i=0; i<BANDS; i++)
		{
			settings[i] = 0.0f;
		}
	}

	
	/**
	 * Retrieves the number of bands present in this equalizer.
	 */
	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.
	 */
	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.
	 */
	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].
	 * 	 
	 */
	float getBandFactor(float eq)
	{
		if (eq==BAND_NOT_PRESENT)
			return 0.0f;
		
		float f = (float)Math.pow(2.0, eq);
		return f;
	}
	
	
	static 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.
		 */
		public float getBand(int band)
		{
			return 0.0f;	
		}
		
	}
		
}