Sound
Upcoming
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Sound splicing
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Intellectual property
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Network analysis
Reading
Introduction to Computing & Programming in Python:
Chapters 6, 7
CompSci 001 5.1

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The outer ear “catches” sounds
The eardrum vibrates
The inner ear translates the vibrations to nerve impulses for the brain to interpret
CompSci 001
Georgia Institute of Technology
5.2

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Sounds are waves of air pressure
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Sound comes in cycles
The frequency of a wave is the number of cycles per second (cps), or Hertz
• (Complex sounds have more than one frequency in them.)
The amplitude is the maximum height of the wave
Georgia Institute of Technology
CompSci 001 5.3

Volume and Pitch
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Our perception of volume is related (logarithmically) to changes in amplitude
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If the amplitude doubles, it’s about a 3 decibel (dB) change.
A decibel is a ratio between two intensities: 10 * log
10
(I
1
/I
2
)
As an absolute measure, it’s in comparison to threshold of audibility
• 0 dB can’t be heard.
• Normal speech is 60 dB.
• A shout is about 80 dB
Our perception of pitch is related (logarithmically) to changes in frequency
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Higher frequencies are perceived as higher pitches
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We can hear between 5 Hz and 20,000 Hz (20 kHz)
A above middle C is 440 Hz
Georgia Institute of Technology
CompSci 001 5.4

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In calculus you learn to estimate a curve by creating rectangles
We can do the same to estimate the sound curve
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Analog-to-digital conversion (ADC) will give us the amplitude at an instant as a number: a sample
How many samples do we need?
Georgia Institute of Technology
CompSci 001 5.5

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What’s the difference between
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Phonograph and CD?
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VCR tape and DVD?
Why digitize sound?
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How is ripping to a mp3 different from recording to a tape?
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Reproduction: immediate and future
Distribution
Modification
Why do digital media present new challenges from analog media?
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Is copyright infringement new?
CompSci 001 5.6

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We need twice as many samples as the maximum frequency in order to represent (and recreate, later) the original sound.
The number of samples recorded per second is the sampling rate
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If we capture 8000 samples per second, the highest frequency we can capture is 4000 Hz
• That’s how phones work
If we capture more than 44,000 samples per second, we capture everything that we can hear (max 22,000 Hz)
• CD quality is 44,100 samples per second
Call a friend on a phone and play some music over the phone
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How does it sound?
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Why does it work for voice but not for music?
5.7
CompSci 001

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We can create a Sound object just as we created a Picture object
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Get a file name and save a reference to it
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– Pick a file that ends in .wav
Create the sound object by asking the class to create a new
Sound object and initialize it by reading data from the given file name
• sound1 = makeSound(fileName);
Play the Sound play(sound1);
Georgia Institute of Technology
CompSci 001 5.8

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Try creating a Sound object and playing it by
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Specifying it in steps
Specifying it all at once
How would you play the same sound twice?
CompSci 001
Georgia Institute of Technology
5.9

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Each sample is stored as a number (two bytes)
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What’s the range of available combinations?
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16 bits, 2 16 = 65,536
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But we want both positive and negative values
• To indicate compressions and rarefactions.
What if we use one bit to indicate positive (0) or negative (1)?
That leaves us with 15 bits
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CompSci 001
15 bits, 2 15 = 32,768
One of those combinations will stand for zero
• We’ll use a “positive” one, so that’s one less pattern for positives so the range is from -32,768 to 32,767
Georgia Institute
5.10
of Technology

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Not all of the sound is shown when you explore a sound
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Skips values to fit in the window
You can zoom in
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To see all sample values
You can zoom out
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To fit the sound in the window again
CompSci 001
Georgia Institute of Technology
5.11

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A Sound has many values in it
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Numbers that represent the sound at that time in the sample
You can get an list of SoundSample objects
 samples = getSamples(sound1);
CompSci 001
Georgia Institute of Technology
5.12

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You can get the SoundSample object from the list at an index
 sample = samples[0];
And then get the value from that
 print sample
What are the first 10 values of the Sound created from the file croak.wav?
CompSci 001
Georgia Institute of Technology
5.13

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You can set the value of a SoundSample
 setSample(sample, value);
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This will change the value in the Sound object as well
So how would you change the value of the first sample to the original value * 2?
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How could you double all of the samples?
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By hand?
• How many samples are there?
Using a loop?
Georgia Institute of Technology
CompSci 001 5.14

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The index is set to 0
The value is set to the value in the array at that index (59)
The sample value at the current index is set to 2 * value
The index changes to the next index (1)
We check if the index is less than the length of the array and
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If so do the loop again
Else jump to the first statement after the loop
Georgia Institute of Technology
CompSci 001 5.15

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When we read from a file we read from disk into memory
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Computers only do calculations on memory
We change the values in memory
The file on the disk hasn’t changed
To save our new sound we need to write a file to the disk
 writeSoundTo(sound1, fileName);
CompSci 001
Georgia Institute of Technology
5.16

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US Constitution (Article I, Section 8, Clause 8):
“To promote the Progress of Science and useful Arts”
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What can you copyright?
• Fixed, tangible medium of expression with a modicum of originality
How do you copyright?
• Don’t need anything. Registration necessary for copyright infringement suits
Authors given limited monopoly so they will disclose to public
Concessions
1. Fair use
2. First sale
3. Limited Time
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Evolving Bargain: Copyright holder may profit from works and public has access and can build upon them
What would happen if information could only be shared if the owner provided permission?
CompSci 001
Georgia Institute of Technology
5.17

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Use copyrighted works without permission if the use does not unduly interfere with the copyright owner’s market for a work
Include personal, noncommercial uses
4 prong test
1.
Purpose and character of use (commercial vs. non-profit or educational)
2.
3.
4.
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Nature of copyrighted work
Amount and substantiality of the portion used
Effect of the copying upon market
Example: using a VCR to time-shift a broadcast program
Reverse engineering
OK when extracting unprotected elements
Connectix Virtual PlayStation
CompSci 001
Georgia Institute of Technology
5.18

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Idea: copying is hard to control, so make the copying process itself difficult
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Restrict the use of digital files in order to protect interest of copyright holders
Control file access
Implemented in operating system, program software, or in the actual hardware of a device
Digital watermarking
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Make information so that unauthorized copying can be detected
Serial Copy Management System (Audio Home
Recording Act 92)
Dystopian and utopian results?
Privacy issues?
CompSci 001
Georgia Institute of Technology
5.19

Artist Def Jeff creates a new song that includes a four-bar percussion sample from a Rolling Stones song. He uses the sample without receiving permission from the copyright holder, His DJ overlays the track containing the sample with 40 tracks of original music and puts the song on his latest CD.
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Were Def Jeff’s actions within the limits of fair use?
Would he lose a lawsuit?
5.20
of Technology