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You will find listings of the source code used to create these melodies later in this module.
The code in Listing 4 uses the standard procedure to either play or file the melody that was created in Listing 3 .
| Listing 4 . Play or file the melody. |
|---|
new AudioPlayOrFile01(audioParams,melody,this.args[0]).playOrFileData();}//end constructor
//-------------------------------------------------------------------------//}//end class MusicComposer08.java |
While this may seem like a rather innocuous result, runtime polymorphism is an extremely important concept in object-oriented programming. One of theimportant applications of runtime polymorphism is the Java Collections Framework . A series of accessible modules that explain the framework begins with Java4010 : Getting Started with Java Collections .
I encourage you to copy the code from Listing 5 through Listing 16 . Compile the code and execute it. Experiment with the code,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.
This section contains a variety of miscellaneous information.
Financial : Although the OpenStax CNX site makes it possible for you to download a PDF file for the collection thatcontains this module at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, youshould be aware that some of the HTML elements in this module may not translate well into PDF.
You also need to know that Prof. Baldwin receives no financial compensation from OpenStax CNX even if you purchase the PDF version of the collection.
In the past, unknown individuals have copied Prof. Baldwin's modules from cnx.org, converted them to Kindle books, and placedthem for sale on Amazon.com showing Prof. Baldwin as the author. Prof. Baldwin neither receives compensation for those sales nordoes he know who does receive compensation. If you purchase such a book, please be aware that it is a copy of a collection thatis freely available on OpenStax CNX and that it was made and published without the prior knowledge of Prof.Baldwin.
Affiliation : Prof. Baldwin is a professor of Computer Information Technology at Austin Community College inAustin, TX.
Complete listing of the twelve classes required by the program discussed in this module are provided below.
| Listing 5 . The class named AudioGraphSinusoidal. |
|---|
/*File AudioGraphSinusoidal.java
Copyright 2014, R.G.BaldwinRevised 08/23/14
This class can be used to create an 8-second melody consisting of 32 pulsesat different frequencies.
******************************************************************************/import java.io.*;
import java.nio.*;import java.util.*;
public class AudioGraphSinusoidal extends AudioSignalGenerator02{public AudioGraphSinusoidal(AudioFormatParameters01 audioParams,String[] args,byte[] melody){super(audioParams,args,melody);
}//end constructor//-------------------------------------------------------------------------////This method returns a melody array that will play an 8-second melody
// consisting of 32 pulses at different frequencies. The frequencies of the// pulses are centered on middle-C (261.63 Hz).//The frequency deviation from middle-C versus time is based on a sinusoidal
// function with a frequency of 0.5 Hz. Each pulse represents one point on// a graph of the sinusoid. Pulses with frequencies at or above middle-C are
// delivered to the left speaker. Pulses with frequencies below middle-C are// delivered to the right speaker.
//The audio output can be thought of as an audio representation of a graph// of a sinusoid. Pulses with frequencies above middle-C represent points
// on the positive lobe of the sinusoid. Increasing pitch represents// increasing amplitude on the graph of the sinusoid. Pulses with
// frequencies below middle-C can be thought of as representing points on// the negative lobe of the sinusoid. In this case, decreasing pitch
// represents points on the sinusoid that are further from the horizontal// axis in the negative direction. Pulses with a frequency of middle-C can
// be thought of as representing points on the horizontal axis with a value// of zero.
//In order to eliminate pops and clicks caused by abrupt frequency changes// in the audio signal, the amplitude of each pulse is scaled by a
// triangular (rooftop) function that has a value that is zero at both ends// and 1.0 in the center with a linear progression from the center to the
// ends in both directions.//Four complete cycles of the 0.5 Hz sinusoid are represented by the 32
// pulses in the 8-second melody.byte[]getMelody(){
//Set channels to 2 for stereo overriding the default value of 1.audioParams.channels = 2;
System.out.println("audioParams.channels = " + audioParams.channels);//Each channel requires two 8-bit bytes per 16-bit sample.
int bytesPerSampPerChan = 2;//Override the default sampleRate of 16000.0F. Allowable sample rates// are 8000,11025,16000,22050, and 44100 samples per second.
audioParams.sampleRate = 8000.0F;// Specify the length of the melody in seconds.double lengthInSeconds = 8.0;//Set the center frequency. Audio pulses will be generated above and
// below this frequency to represent points on the graph of a// sinusoidal function.
double centerFreq = 261.63;//middle C//Create an output array of sufficient size to contain the melody at
// "sampleRate" samples per second, "bytesPerSampPerChan" bytes per// sample per channel and "channels" channels.
melody = new byte[(int)(lengthInSeconds*audioParams.sampleRate*bytesPerSampPerChan*audioParams.channels)];System.out.println("melody.length = " + melody.length);//Declare variables used to control the output volume on the left and
// right speaker channels. These values will be used to cause pulses// representing negative values of the sinusoidal function to emit from
// one speaker and pulses representing positive values to emit from// the other speaker.
double gain = 0.0;double leftGain = 0.0;
double rightGain = 0.0;//Declare a variable that is used to control the frequency of each pulse.
double freq = 0.0;//Prepare a ByteBuffer for use
byteBuffer = ByteBuffer.wrap(melody);//Compute the number of audio samples in the melody.
int sampLength = (int)(lengthInSeconds*audioParams.sampleRate);//Set the length of each pulse in seconds and in samples.
double pulseLengthInSec = 0.25;//in secondsint pulseLengthInSamples = (int)(pulseLengthInSec*audioParams.sampleRate);
//Compute the audio sample values and deposit them in the output melody// array.
for(int cnt = 0; cnt<sampLength; cnt++){
//Compute the time in seconds for this sample.double time = cnt/audioParams.sampleRate;if(cnt%pulseLengthInSamples == 0){
//Time to create a new pulse at a different pitch. Compute the// frequency for the next pulse to represent a point on a sinusoidal
// function of time. This section of code could easily be modified// to create audio graphs of many different functions.//Evaluate and scale the function
double val = 0.35 * Math.sin(2*Math.PI*0.5*time);//Compute the frequency for the next pulse as a deviation from the// center frequency. For this scaled sinusoidal function, the Range
// is from 0.65*centerFreq to 1.35*centerFreq or from 170.05 Hz// to 353.2 Hz.
freq = (1+val)*centerFreq;}//end if
//Deposit audio data in the melody for each channel. Scale the amplitude// of each pulse with a triangular scale factor (rooftop shape) to
// minimize the undesirable pops and clicks that occur when there is an// abrupt change in the frequency from one pulse to the next. The
// following gain factor ranges from 0.0 at the ends to 1.0 in the// center of the pulse.
gain = (cnt%pulseLengthInSamples)/(double)pulseLengthInSamples;if(gain>0.5){
//Change to a negative slope.gain = (pulseLengthInSamples -
cnt%pulseLengthInSamples)/(double)pulseLengthInSamples;}//end if//Set the final gain to a value that is compatible with 16-bit audio
// data.gain = 8000*gain;
//Switch the left and right channels on and off depending on the location// of the pulse frequency relative to the center frequency.
if(freq>= centerFreq){
leftGain = gain;rightGain = 0;//switch off the right channel
}else{rightGain = gain;
leftGain = 0;//switch off the left channel}////Compute scaled pulse values and deposit them into the melody.
byteBuffer.putShort((short)(leftGain*Math.sin(2*Math.PI*freq*time)));byteBuffer.putShort((short)(rightGain*Math.sin(2*Math.PI*freq*time)));
}//end for loopreturn melody;}//end method getMelody
//-------------------------------------------------------------------------//}//end class AudioGraphSinusoidal
//===========================================================================// |
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