Montana Tech of The University of Montana
Computer Science & Software Engineering

CSCI 135
Fundamentals of Computer Science I
Fall 2011


In this assignment, you will will be implementing a variety of static methods. You will obtain additional practice creating and using arrays.

Audio Effects
You are tasked with completing a command line utility that lets users mix and mash audio files. Using simple starting sounds, users can create a masterpiece of audacious audio. Using the utility, users can cut out sections of sound, add leading and trailing silence, add echoes, merge sounds, reverse sounds, and loop sounds. Lucky a previous developer has already implemented the main() method and a handful of the utility's effects (play, stats, and gain). Your task is to complete methods for the reverse, loop, merge, echo, cut and pad audio effects. Here is an example mix created from this set of commands.

To start with, download the file and unzip it to your project directory. This file contains the existing source code as well as a selection of audio files for your testing pleasure. You will be using to handle the loading and playback of audio. StdAudio provides access to the audio samples in a WAV format audio file via a double [] array. All your audio manipulating methods will operate by manipulating and returning double [] arrays. You should not change the double [] array passed as input to your methods. Rather you should create a new double [] array, fill it with values, and return it from each method (for an example see the audioGain() method).

Each audio sample in a file is representing by a double value, typically between -1.0 and +1.0. Values outside this range are clipped to -1.0 or +1.0 during playback. The bigger the absolute value of the double value, the louder the sound is at that point in the file. All the provided audio files are recorded at 44100 samples per second so as to work with StdAudio. If want to try your program with your own audio files, make sure they are WAV format, recorded at 44100 samples per second, 16-bit, mono, signed format. If you want to convert files in a different format, various programs such as GoldWave can do this.

The provided file is partially completed. You need to fill in the method bodies for audioReverse(), audioLoop(), audioMerge(), and audioCut(). You need to add all of the audioPad() and audioEcho() methods as well as the calls to audioPad and audioEcho in the main method. Before each method, you'll find a detailed comment describing what the method does, its parameters, and its return values. Users of your utility may not always make the most sensible requests (e.g. asking to loop an audio clip -43 times). Your program should defend itself against such silly requests and not crash. In the case of bad input to your method, simply return an appropriate failure value as specified by the method comment (typically null).

The first example usage below shows the command line arguments taken by the program. The first argument is always the filename of the WAV file. The second argument is always one of the effect names given as a string (e.g. "play", "stats", "reverse", "gain"). After this, there are zero or more additional arguments depending on the type of effect.

What is this null value? Variables of reference type (which includes arrays) can be assigned a value of null. A variable set to null refers to no object (though the variable could refer to an object in the future). We use it in this assignment to allow our methods to inform the caller via the double [] return result that something went wrong and no audio result is available.

How do I convert from a time in seconds to a sample index? All the audio in this assignment is sampled at 44100 samples per second (declared as a constant SAMPLING_RATE in If you multiply the time in seconds by SAMPLING_RATE you will get the sample number. In our reference solution, we dropped the decimal portion by casting this calculated value to an int. In general, you should avoid putting "magic numbers" such as 44100 in your code and instead use a declared constant such as SAMPLING_RATE. This is better style as the name tells the reader what it means and also makes it easy to change the value everywhere by one simple change.
Example usage:
% java AudioEffects 
AudioEffects <infile> <effect> [options]

  play                                - play the file
  stats                               - print some stats about the audio
  reverse                 <out file>  - reverse an audio file
  gain    <factor>        <out file>  - change the volume by given factor
  loop    <times>         <out file>  - loop audio given number of times
  merge   <infile2>       <out file>  - merge two audio files together
  cut     <start> <end>   <out file>  - clip audio from [start, end] seconds
  pad     <start> <end>   <out file>  - add silence to start and/or end
  echo    <secs> <factor> <out file>  - add an echo to audio

Supports only 44.1 kHz mono 16-bit signed WAV audio files.
% java AudioEffects piano.wav reverse piano_reverse.wav
Effect: reverse
Wrote 226800 samples to piano_reverse.wav

% java AudioEffects piano_reverse.wav stats
Effect: stats
Samples          :       226800
Length (s)       :     5.142857
Average level    :     0.000044
Max level        :     0.434431
Below 1% max (%) :     3.113316
Below 5% max (%) :    15.427690
% java AudioEffects scratch.wav loop 4 scratch_loop4.wav
Effect: loop
Wrote 282036 samples to scratch_loop4.wav

% java AudioEffects scratch_loop4.wav stats
Effect stats
Samples          :       282036
Length (s)       :     6.395374
Average level    :    -0.001621
Max level        :     1.000000
Below 1% max (%) :    34.224000
Below 5% max (%) :    59.749819

% java AudioEffects scratch.wav loop -43 scratch_loop-43.wav
Effect: loop
% java AudioEffects cow.wav merge chimes.wav cow_chimes.wav
Effect: merge
Wrote 275015 samples to cow_chimes.wav

% java AudioEffects cow_chimes.wav stats
Effect: stats
Samples          :       275015
Length (s)       :     6.236168
Average level    :    -0.000075
Max level        :     0.388287
Below 1% max (%) :    28.735524
Below 5% max (%) :    65.232442

% java AudioEffects beatbox.wav merge harp.wav beatbox_harp.wav
Effect: merge
Wrote 89491 samples to beatbox_harp.wav

% java AudioEffects beatbox_harp.wav stats
Effect: stats
Samples          :        89491
Length (s)       :     2.029274
Average level    :     0.000768
Max level        :     0.509171
Below 1% max (%) :    25.547820
Below 5% max (%) :    63.730431
% java AudioEffects dialup.wav cut 4.0 5.0 dialup_cut4-5.wav
Effect: cut
Wrote 44100 samples to dialup_cut4-5.wav

% java AudioEffects dialup_cut4-5.wav stats
Effect: stats
Samples          :        44100
Length (s)       :     1.000000
Average level    :     0.017001
Max level        :     0.324198
Below 1% max (%) :     3.269841
Below 5% max (%) :    24.467120

% java AudioEffects dialup.wav cut 4.0 50.0 dialup_cut4-50.wav
Effect: cut

% java AudioEffects dialup.wav cut 5.0 4.0 dialup_cut5-4.wav
Effect: cut
% java AudioEffects buzzer.wav pad 1.0 2.0 buzzer_pad1-2.wav
Effect: pad
Wrote 216969 samples to buzzer_pad1-2.wav

% java AudioEffects buzzer_pad1-2.wav stats
Effect: stats
Samples          :       216969
Length (s)       :     4.919932
Average level    :    -0.000004
Max level        :     0.997925
Below 1% max (%) :    62.104725
Below 5% max (%) :    66.364319

% java AudioEffects buzzer.wav pad -10.0 -20.0 buzzer_pad-10-20.wav
Effect: pad
% java AudioEffects singer.wav echo 0.5 0.6 singer_echo_0.5_0.6.wav
Effect: echo
Wrote 680597 samples to singer_echo_0.5_0.6.wav

% java AudioEffects singer_echo_0.5_0.6.wav stats
Effect: stats
Samples          :       680597
Length (s)       :    15.433039
Average level    :    -0.000015
Max level        :     0.965667
Below 1% max (%) :    32.031290
Below 5% max (%) :    54.441321

Extra-credit. Using only the audio provided in the file, create an audio mashup. Submit your single best artistic creation along with the step-by-step commands used to generate it. The best mixes will be added to the hall of fame for this assignment. You may add additional effects to AudioEffects if it aids in the creation of your masterpiece. There are many additional sound effects you could add such as fading in/out, adjusting pitch, averaging samples, adding random noise, etc.
Submission. Submit your program using Moodle. Be sure each submitted source file has the required header with your name, username, and a description of the program.

Copyright © 2011 by Keith Vertanen.

Page last updated: August 16, 2012