Digital Instrument Building

Spectral Morphing

This tutorial shows how dynamic timbres can be generated by changing the balance between overtones with amplitude envelopes.
The result in this simple example is like a cross-fade between two samples.
It will indicate how elaborate dynamic sprectra can be created by envelope control over partial loudness.

View / Download source - Instrument source code

View / Download source - Composition source code

The instrument class

import jm.audio.io.*;
import jm.audio.synth.*;
import jm.music.data.Note;
import jm.audio.Instrument;

/**
* An additive synthesis instrument implementation
* which cross fades two different spectra, each
* with five partials.
* @author Andrew R. Brown
*/

public final class AddMorphInst extends Instrument{
            
        //----------------------------------------------
	// Attributes
	//----------------------------------------------
	private int overtones = 10;
            
	/** the relative frequencies which make up this note */
	private double[] freqVals = {1.0, 3.0, 5.0, 7.0, 9.0, 1.0, 2.8, 5.6, 8.4, 11.0};
            
        /** the volumes to use for each frequency */
	private double[] volVals = {1.0, 0.7, 0.5, 0.3, 0.2, 1.0, 0.7, 0.5, 0.3, 0.2};
            
        /** The points to use in the construction of Envelopes */
	private double[][] points = new double[overtones][6];
	private double[] pointArray1 = {0.0, 0.0, 0.02, 1.0, 1.0, 0.0};
	private double[] pointArray2 = {0.0, 0.0, 0.98, 1.0, 1.0, 0.0};
	
            
        /** Pan */
	private float pan;
            
        /** The sample Rate to use */
	private int sampleRate;
            
        /** The Oscillators to use for each frequency specified */
	private Oscillator[] osc;
            
        /** The envelope to apply to each Oscillator's output */
	private Envelope[] env;
            
	/** The volume to apply to each envelopes output */
	private Volume[] vol;	
            
	//----------------------------------------------
	// Constructor
	//----------------------------------------------
	public AddMorphInst(int sampleRate){
		this.sampleRate = sampleRate;
                    
		// set up envelope points
		for (int i=0; i<5; i++) {
			points[i] = pointArray1;
		}
		for (int i=5; i<10; i++) {
			points[i] = pointArray2;
		}
	}
            
	//----------------------------------------------
	// Methods 
	//----------------------------------------------
	/**
	 * Initialisation method is used to build the objects that
	 * this instrument will use
	 */
	public void createChain(){
		
                //define the audio chain(s)
		osc = new Oscillator[overtones];
		env = new Envelope[overtones];
		vol = new Volume[overtones];
		for(int i=0;i
		//And now the add object brings us back to one path.
		Add add = new Add(vol);
		StereoPan span = new StereoPan(add);
		SampleOut sout = new SampleOut(span);
	}
}

Ten partials (overtones) are declared, the first five are for one timbre and the other five for a second timbre.
Two envelopes are used, one with a quick attack followed by a decay applied to the first five partials, the other the reverse,
a slow attack leading to a fast release which is applied to the other five partials.
The assigning of envelopes to partials is done in the two for-loops in the constructor.

The first five partials have frequency ratios (with the fundamental) that are simple odd multiples, thus the sound is somewhat like a square wave or clarinet.
The later five partials have ratios that result in inharmonic frequencies which produces a sharsher bell-like timbre
(but, of course, without the attack).
The resulting sound shifts fro one timbre to the other as the amplitude of the partial sets shifts,
resulting is a morphing or cross-fade between the two spectra.

Musical Example

import jm.JMC;
import jm.music.data.*;
import jm.audio.*;
import jm.util.*;
public final class AddMorphTest implements JMC{
	public static void main(String[] args){
		Score score = new Score("JMDemo - Additive Synthesis test");
		Part part = new Part("Spectra Notes", 0);
		Phrase phr = new Phrase(0.0);
		int sampleRate = 44100;
		Instrument inst = new AddMorphInst(sampleRate);
		Note note = new Note(C3, 8.0);
		phr.addNote(note);
		part.addPhrase(phr);
		score.addPart(part);
		Write.au(score, "AddMorphTest.au", inst);
	}
}

The code above uses the instrument to render a simple jMusic score.