1. Processing Sound Ranges part 3
Barb Ericson
Georgia Institute of Technology
Oct 2009
UsingSoundRanges-part3

2. UsingSoundRanges-part3
Learning Goals
Processing ranges of Sound values
Creating echoes
Changing the sound frequency
Computing concepts
Changing a for loop to increment by a value other than 1
Modifying a method to be more general
UsingSoundRanges-part3

3. UsingSoundRanges-part3
Echo
By blending a sound with itself we can make an echo
Add the sound values to the same sound but after some delay
UsingSoundRanges-part3

4. UsingSoundRanges-part3
Method echo
public void echo(int delay) { // make a copy of the original sound Sound s = new Sound(this.getFileName()); int value = 0; // loop from delay to end of sound for (int i = delay; i < this.getLength(); i++)
UsingSoundRanges-part3

5. UsingSoundRanges-part3
Method echo continued
/* get the value back by delay samples from the
* copy of the sound and make it fainter */
value = (int) (s.getSampleValueAt(i-delay) * 0.6);
/* set the value at the current index to the sum
* of the current value and the echo */
this.setSampleValueAt(i,
this.getSampleValueAt(i) +
value); }
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6. UsingSoundRanges-part3
Test the echo method
String fileName = FileChooser.getMediaPath(
"thisisatest.wav");
Sound sound = new Sound(fileName);
sound.explore();
sound.echo(20000);
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7. UsingSoundRanges-part3
How does that work?
The echo method takes an integer delay
The number of samples to wait before starting the echo
It makes a copy of the current sound
So that we copy without the echo
Loop starting from delay to the end of the sound
Get the value at i-delay and multiply it by 0.6 to make it quieter
Set the current sound value at i to the current value at i plus the calculated value
UsingSoundRanges-part3

8. Creating Multiple Echoes
You can use a nested loop to create multiple echoes
Here is an example nested loop in Alice
UsingSoundRanges-part3

9. Creating Multiple Echoes Method
public Sound echo(int delay, int numEchoes) { int soundLength = this.getLength(); Sound echoSound = new Sound(numEchoes * delay + soundLength); int value = 0; int echoIndex = 0; int echoValue = 0; double echoAmplitude = 1; // to start // copy the original sound echoSound.splice(this,0,soundLength,0); /* loop starting with 1 to create the first echo at the * right place and end when = the number of echoes */
UsingSoundRanges-part3

10. Multiple Echoes - continued
for (int echoCount = 1; echoCount <= numEchoes; echoCount++) { // decrease the volume (amplitude) of the echo echoAmplitude = echoAmplitude * 0.6; // echo the whole sound for (int i = 0; i < soundLength; i++) echoIndex = i + (delay * echoCount); echoValue = (int) (this.getSampleValueAt(i) * echoAmplitude); echoSound.setSampleValueAt(echoIndex,echoValue + echoSound.getSampleValueAt(echoIndex)); } return echoSound;
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11. UsingSoundRanges-part3
Try Multiple Echoes
Sound s = new Sound( FileChooser.getMediaPath("croak.wav")); Sound e = s.echo(8000,5); e.play();
UsingSoundRanges-part3

12. Changing the Sound Frequency
The frequency of a wave is the number of cycles per second (cps), or Hertz (Hz)
(Complex sounds have more than one frequency in them.)
Our perception of pitch is related (logarithmically) to changes in frequency
Higher frequencies are perceived as higher pitches
We can hear between 5 Hz and 20,000 Hz (20 kHz)
A above middle C is 440 Hz
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13. UsingSoundRanges-part3
Double the Frequency
If we take every other sample we double the frequency of the sound
Completes two cycles instead of one in the same time
It will sound higher
100 | 200 | 300 | 400 | 500
100 | 300 | 500 | 0 | 0
UsingSoundRanges-part3

14. Double Frequency Method
public void doubleFreq() {
// make a copy of the original sound
Sound s = new Sound(this.getFileName());
/* loop and increment target index
* by one but source index by 2,
* and set target value
* to the copy of the original sound */
UsingSoundRanges-part3

15. Double Frequency - Continued
for (int sourceIndex=0, targetIndex = 0;
sourceIndex < this.getLength();
sourceIndex=sourceIndex+2, targetIndex++)
this.setSampleValueAt(targetIndex,
s.getSampleValueAt(sourceIndex));
// clear out the rest of this sound to silence (0)
for (int i = this.getLength() / 2;
i < this.getLength();
i++)
this.setSampleValueAt(i,0); }
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16. UsingSoundRanges-part3
Test Double Frequency
Sound s = new Sound(FileChooser.getMediaPath(
"c4.wav"));
s.explore();
s.doubleFreq();
The file c4.wav is the note C played on a piano in the fourth octave.
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17. UsingSoundRanges-part3
Challenge
Create a method that will take every third sample
Will this sound higher or lower?
Can you make this method more general?
By passing in the amount to add to the source index each time?
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18. UsingSoundRanges-part3
Halving the Frequency
We can copy each source value twice to half the frequency
Only get through half a cycle in the same time we used to get through a full cycle
It will sound lower
100 | 200 | 300 | 400 | 500
100 | 100 | 200 | 200 | 300
UsingSoundRanges-part3

19. Halve Frequency Method
public void halveFreq() {
// make a copy of the original sound
Sound s = new Sound(this.getFileName());
/* loop through the sound and increment target index
* by one but source index by 0.5 and set target value
* to the copy of the original sound */
for (double sourceIndex=0, targetIndex = 0;
targetIndex < this.getLength();
sourceIndex=sourceIndex+0.5, targetIndex++)
this.setSampleValueAt((int) targetIndex,
s.getSampleValueAt((int) sourceIndex)); }
UsingSoundRanges-part3

20. Testing Halve Frequency
Sound s = new Sound(FileChooser.getMediaPath(
"c4.wav"));
s.explore();
s.halveFreq();
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21. UsingSoundRanges-part3
Challenge
Write a method that will copy each sound value 4 times to the target
Will the new sound be higher or lower?
Can you make this more general?
By passing in the number of times to copy the source value
Try it with 3 times and check the index values to make sure that you are doing it right
You can add 0.5 and 0.25 and the (int) of that will work fine. But, you can have trouble with things like 1/3 which is (and so on). Computers can’t do infinite numbers. So, they have to approximate them. So adding .33 each time will not get over 1 the way it should.
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22. UsingSoundRanges-part3
Summary
You can increment or decrement loop variables by numbers other than 1
You can make methods more general
By passing in parameters
UsingSoundRanges-part3