# 6.4.4. Free Response - Sound A¶

The following is a free response question from 2011. It was question 1 on the exam. You can see all the free response questions from past exams at https://apstudents.collegeboard.org/courses/ap-computer-science-a/free-response-questions-by-year.

Question 1. Digital sounds can be represented as an array of integer values. For this question, you will write two unrelated methods of the Sound class.

A partial declaration of the Sound class is shown below.

public class Sound
{
/** the array of values in this sound; guaranteed not to be null */
private int[] samples;

/** Changes those values in this sound that have an amplitude
*  greater than limit */
*  Values greater than limit are changed to limit.
*  @param limit the amplitude limit
*         Precondition: limit >= 0
*  @return the number of values in this sound that this
*         method changed
*/
public int limitAmplitude(int limit)
{ /* to be implemented in part (a) */ }

/** Removes all silence from the beginning of this sound.
*  Silence is represented by a value of 0.
*  Precondition: samples contains at least one nonzero value
*  Postcondition: the length of samples reflects the removal
*               of starting silence
*/
public void trimSilenceFromBeginning()
{ /* to be implemented in part (b) */ }

// There may be instance variables, constructors, and methods
// that are not shown.
}


Part a. The volume of a sound depends on the amplitude of each value in the sound. The amplitude of a value is its absolute value. For example, the amplitude of -2300 is 2300 and the amplitude of 4000 is 4000.

Write the method limitAmplitude that will change any value that has an amplitude greater than the given limit. Values that are greater than limit are replaced with limit, and values that are less than -limit are replaced with –limit. The method returns the total number of values that were changed in the array. For example, assume that the array samples has been initialized with the following values.

When the statement

int numChanges = limitAmplitude(2000);


is executed, the value of numChanges will be 5, and the array samples will contain the following values.

## 6.4.4.1. How to Solve This¶

FRQ Sound A: Write the method limitAmplitude that will change any value that has an amplitude greater than the given limit. Values that are greater than limit are replaced with limit, and values that are less than -limit are replaced with –limit. The method returns the total number of values that were changed in the array. The main method has code to test your solution.