CSC111 JES Page on Sound Processing

--D. Thiebaut (talk) 20:12, 23 February 2014 (EST)

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Reference

• JES's reference page from Depauw University
• Lab 7 CSC111 2010

Installation

Sound Files

• Get some sample wav files:

• hello.wav
• goodbye.wav
• dratcomp.wav
• force.wav
• takeover.wav
• guitar.wav

• Note: There's more at http://buggerluggs.tripod.com/ie/wav-dir184.htm and http://www.duke.edu/~rfb/palace/wavs/dratcomp.wav. If you want to download more to your account, simply find the URL of a wav file, for example http://www.duke.edu/~rfb/palace/wavs/energize.wav, and download it to your computer.

If you want to install JES on your personal Windows computer

If you want to install JES on your Windows laptop or computer, you can get Jes from the Google code web site. Grab the 3.2.1 version for Windows and install it on your Windows machine.

If you want to install JES on your personal Mac

Jes for the Mac is available on Google code. Get Jes 3.2.1 for the Mac, open the zip file, and move the JES 3.2.1.app to your Applications folder.

Example 1: Playing Sound Files

• In the JES program area, type in the following main() function:

file = pickAFile()
sound = makeSound( file )
blockingPlay( sound )

• Save the file as sound1.py
• Click on Load Program
• In the interactive area, type

• When prompted for a sound file, select thisisatest.wav in the Sound Files folder.
• Make sure the speakers are on, but not too loud and listen to the sentence being played.
• Try one or two other sound files.

Part 3: Altering a sound file

• You will reduce the intensity of the sound by dividing all the samples by half
• Copy/Paste the program below in JES
• Read it to make sure you understand it.

  # select  a sound file
  file = pickAFile()
  sound = makeSound( file )

  # play it
  blockingPlay( sound )

  # lower its intensity by half
  for i in range( 1, getLength( sound ) ):
     value = getSampleValueAt( sound, i )    # get the value of the i-th sample
     setSampleValueAt( sound, i, value / 2 )  # set the sample to half its original value

  # play new waveform back
  blockingPlay( sound )

Part 4: Reversing a Sound File

• The goal is to create 2 sound objects, sound1 and sound2 from the same file, and take the value of the sample at Index 1 in sound1 and to store it at Index N-1 in sound2. Identically for the sample at Index 2 which will go to Index N-2 in sound2.

• Complete the table below and write down the relationship existing between i and j:

i	j	i+j
1
2
3
...
N-2
N-1

• From the table above extract the equation that yields j as a function of i
• Write your for-loop to reverse sound1 into sound2

      N = ...
      for i in range( 1, N ):
           j = ...
           sample = getSampleValueAt( sound1, i )
           setSampleValueAt( sound2, j, sample )

• Test your program by making it play sound1 first, then sound2.

Part 9: ECHO Echo echo

Same as Part 8, but now you will make 2 copies of your sound object, attenuate the first one by 0.5, the second one by 0.25, and delay each by 5000 from each other, and create a reverberation effect.

JES Sound Functions

This is just reference material taken from Depaw U. that you may want to play with.

A sound is treated as a collection of sample values, much as a picture is a collection of pixels. Here are the functions on sounds:

makeSound(file)	Return a sound loaded from a WAV, AU, or AIFF file
makeEmptySound(sec)	Return a blank sound (all samples 0) of length sec seconds
writeSoundTo(s, file)	Save s in the given file; uses the same format as when loaded (makeEmptySound creates a sound in WAV format)
openSoundTool(s)	Open the sound exploration window for s
play(s)	Play sound s in the background
playAtRate(s, r)	Play s at speed r--1.0 is normal, 2.0 is twice as fast, etc.
playInRange(s, b, e)	Play s from sample number b to e
playAtRateInRange(s, r, b, e)	Play s from b to e at speed r
blockingPlay(s)	Play s and wait for it to finish (also, blockingPlayInRange and blockingPlayAtRateInRange)
getSamples(s)	Return the collection of samples in s (not quite a list, but indexable and usable in a for loop)
getLength(s)	Return the number of samples in s
getSamplingRate(s)	Return the number of samples per second in s

There are also some useful methods on sound and sample objects:

s.getSampleValue(i)	Return the (left channel, if stereo) value of the ith sample in s (the first sample is at index 1)
s.getLeftSampleValue(i)	Return the left channel value at index i
s.getRightSampleValue(i)	Return the right channel value at index i
s.setSampleValue(i, v)	Set the (left) value of sample i to v; the range of sample values is -32,768 to +32,767
s.setLeftSampleValue(i, v)	Same
s.setRightSampleValue(i, v)	Guess what?
s.getSampleObjectAt(i)	Extracts the sample object at index i, without creating a whole collection of samples
samp.value	Return the value of sample samp; change the value by assigning to this
samp.left	Return or change the left channel value of samp
samp.right	Return or change the right channel value of samp

Finally, JES provides a simple function to play a MIDI note:

playNote(n, dur, vol)

plays note number n (middle C is 60, C-sharp is 61, etc.; the range is 0-127) for dur milliseconds at volume vol (maximum is 127).

The function pauses execution until the note is finished. For much more complete support of MIDI music, see the next section.