17 - Sound Processing

Goals

Class Sound: stores and manipulates a sound
Initially, this is a simple class with
- a constructor for creating a Sound from a Sample
- a method getSample() that returns the Sample for the Sound
Here is the initial API for class Sound
Notice that the constructor makes a copy of the Sample passed as a parameter and method getSample returns a copy of the sample for the Sound
- This protects the Sound from client code, preventing the client code from changing the actual sample of the Sound
We will write methods in class Sound that manipulate a Sound's sample

Sketch that creates a Sound and calls method getSample(): SoundTest
Study method copy()
- The method is private because it is for use only in the class itself
Exercise: Write a constructor for Sound that has a String parameter for the name of a file containing a sound. The sound format is .aiff or .wav. Modify the SoundTest sketch to use this constructor with sound file bassoon-c4.wav.

To change the volume (amplitude) of a sound, multiply the sample values
Exercise: Write and test Sound method increaseVolume() that doubles the volume of the sound. Remember to constrain sample values to be between -1.0 and 1.0
Exercise: Write and test Sound method changeVolume(aFactor) that changes the volume of the sound by a passed factor. Remember to constrain sample values to be between -1.0 and 1.0

Normalizing a sound means to make it as loud as possible
Algorithm:
- Find the largest sample in the sound, largest
- Loop through all samples, multiplying each sample by largest
To find the largest sample, assign largest value -1. Loop through all samples; if a sample is greater than largest, save that value as largest
Exercise: Write and test Sound method normalize() that normalizes the sound.

Clipping occurs when a sound generates a pressure greater than 1.0, or a rarefaction less than -1.0, and such values are sampled as 1.0 or -1.0, respectively
Exercise: Write and test Sound method forceToExtremes() that sets all non-negative sample values to the maximum positive value (1.0) and all negative sample values to the minimum negative value (-1.0).

A sound clip is a copy of a part of a sound
A sound clip of a sampled sound has a start index and an end index. The number of samples in the clip is (end index) - (start index) + 1
Exercise: Write and test Sound method clip(aStart, aEnd) that clips the sound from a given start index to a given end index.

To splice sounds, copy elements around in the sample arrays
Exercise: Write and test Sound method splice(aSound, aSourceStart, aSourceStop, aTargetStart) that copies part of a given sound into this sound, at a given start index.

To reverse a sound, reverse its sample array
Exercise: Write and test Sound method reverse() that reverses the sound.

To mirror a sound, mirror its sample array about the middle index of the array
Exercise: Write and test Sound method mirror() that mirrors the sound front to back.

To add two sounds, add their sample arrays, element by element
Exercise: Write and test Sound method add(aSound) that adds a given sound to the sound.

To create an echo of a sound, add a scaled copy of the sound after a number of delay samples.
Exercise: Write and test Sound method echo(aDelay, aNumEchoes) that creates multiple echoes of the sound after a given number of delay samples. Try scaling by 0.6.

To double the frequency of a sample, take every second sample value.
Exercise: Write and test Sound method doubleFrequency() that doubles the frequency of this sound.
To halve the frequency of a sample, take each sample value twice.
Exercise: Write and test Sound method halveFrequency() that halves the frequency of this sound.
Exercise: Write and test Sound method changeFrequency(aFactor) that changes the frequency of this sound by a given factor.

Exercise: Write and test static Sound method createSineWave(aFrequence, aMaxAmplitude) that returns a Sound which is a one second sine wave with the given frequency and maximum amplitude.
Exercise: Write and test static Sound method createSquareWave(aFrequence, aMaxAmplitude) that returns a Sound which is a one second square wave with the given frequency and maximum amplitude.
Exercise: Write and test static Sound method createSawtoothWave(aFrequence, aMaxAmplitude) that returns a Sound which is a one second sawtooth wave with the given frequency and maximum amplitude.