SimpleLPCFilter.java

/*
  SimpleLPCFilter.java

  (c) 2012-2013 Edward Swartz

  All rights reserved. This program and the accompanying materials
  are made available under the terms of the Eclipse Public License v1.0
  which accompanies this distribution, and is available at
  http://www.eclipse.org/legal/epl-v10.html
 */
package v9t9.engine.speech.encode;

/**
 * @author ejs
 *
 */
public class SimpleLPCFilter implements ILPCFilter {
	private float[] fa;
	private float u1;
	private float yp1;
	private float yp2;
	private int framelen;
	private int FS;

	private static float FC = 200.0f; /* Pitch analyzer filter cutoff */
	/**
	 * 
	 */
	public SimpleLPCFilter(LPCEncoderParams params) {
		fa = new float[6];
		framelen = params.getFrameSize();
		FS = params.getHertz();
		
		float r, v, w, wcT;
		wcT = (float) (2 * Math.PI * FC / FS);
		r = 0.36891079f * wcT;
		v = 0.18445539f * wcT;
		w = 0.92307712f * wcT;
		fa[1] = (float) -Math.exp(-r);
		fa[2] = 1 + fa[1];
		fa[3] = (float) (-2 * Math.exp(-v) * Math.cos(w));
		fa[4] = (float) Math.exp(-2.0f * v);
		fa[5] = 1 + fa[3] + fa[4];
		
	}


	/* (non-Javadoc)
	 * @see v9t9.engine.speech.encode.ILPCEngine#filter(float[], float[], int, int)
	 */
	@Override
	public void filter(float[] in, int offs, int len, float[] out, float[] y) {
		int i,j;
		for (i = 0, j = len - framelen; i < framelen; i++, j++) {
			out[j] = in[i + offs];
			float u = fa[2] * out[j] - fa[1] * u1;
			y[j] = fa[5] * u1 - fa[3] * yp1 - fa[4] * yp2;
			u1 = u;
			yp2 = yp1;
			yp1 = y[j];
		}
	}
	

}