CS 101 - Introduction to Computing, Spring 2007

Lab 10

Reminder

In the ACCC Labs that have JES, it can be found by:

1. Clicking on Start
2. Then click on All Programs
3. Then click on Class Applications
4. Then click on Engineering
5. Finally click on Jython Environment for Students

Converting from Seconds to Sample Index

This lab assignment will have you write a function that will play a portion of a sound file. The JES function playInRange() will be the basis of our new function. However, we want to specify the portion using seconds and playInRange() uses index position to specify the starting and stopping locations of the sound. Thus we will need to convert from a position in seconds to a position index.

The JES function getSamplingRate () will allow us to convert from index to seconds and seconds to index. This function returns the number of samples in each second. Thus if we know the total number of samples in a sound (this can be gotten from getLength()), we can determine the length in seconds by dividing by the sampling rate. However, if we know a position in seconds, we can determine the sample index by multiplying by the sampling rate.

The following functions will be useful with this assignment.

getLength	getLength(sound): sound: the sound you want to find the length of. returns: the number of samples in sound. Takes a sound as input and returns the number of samples in that sound.
getSamplingRate	getSamplingRate(sound): sound: A Sound, the sound you want to get the sampling rate from. returns: An Integer representing the number of samples per second. Takes a sound as input and returns the number representing the number of samples in each second for the sound
playInRange	playInRange(sound, start, stop): sound: A Sound, the sound you want to play a piece of. start: A Number, the index of the sound you want the playback to start. stop: A Number, the index of the sound you want the playback to stop. Take a sound, a start index, and a stop index and plays a selection of the sound defined by the start and stop indexes.

Lab Assignment 10

Create a file using JES that will:

1. Contain a comment indicating
   • your Name,
   • Net-ID,
   • Course Name,
   • Assignment Name and
   • a short description of the assignment

2. Contain a JES function called playSoundBetween () that will
   • take 3 parameter values:
     1. a sound object
     2. a number specifying where you want the playback to start in seconds
     3. a number specifying where you want the playback to stop in seconds
   • verify that the start value is less than the stop value.
   • convert the second values to index positions
   • verify that the start and stop indexes are within the range of valid sample indexes for the sound
   • play the sound with in the specified range.
   If one of the verification checks fail, print out a descriptive error message and return from the function without playing the sound. The time in seconds can be given as a floating point number (with a decimal point). So you can play from 2.25 seconds to 4.875 seconds.

   Note: The time of the beginning of a sample is 0 seconds. However, the first sample has index of 1. Because of this, you may need to add 1 to the result of the sound to index conversion.

3. Contain a JES driver function that will:
   • prompt the user to open a sound file using pickAFile()
   • create a sound abject from the file
   • call the function playSoundBetween() with this sound value. The values for the time in seconds can be "hardcoded" in your code.

Here are some example sound files you can use with this assignment.

• Gettysburg Address - gettysburg.wav
• Preamble of the US Constitution - preamble.wav

Submittal of the Lab Assignment

• You are submit your program electronically by placing it in the digital drop box in blackboard.
• Programs that are correct and submitted by noon on the Wednesday the lab assignment is discussed will receive an extra 10% on the score of the lab.
• When saving your program, use a meaningful name like lab10.py.
• When submitting your lab assignment, place all of the needed files it in a zippped folder (even if you are only submitting one file) with the name of yournetid_labNum and submit that zipped folder to the digital drop box. For instance, if your net id is abc32 then the folder name should be abc32_lab10.

Comments on the ACCC Labs