CompSci Today’s topics Sound Upcoming ä Sound splicing ä Intellectual property ä Network analysis Reading Introduction to Computing & Programming in Python: Chapters 6, 7

CompSci Georgia Institute of Technology How does Hearing Work? l The outer ear “catches” sounds l The eardrum vibrates l The inner ear translates the vibrations to nerve impulses for the brain to interpret

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

CompSci Georgia Institute of Technology Volume and Pitch l Our perception of volume is related (logarithmically) to changes in amplitude ä If the amplitude doubles, it’s about a 3 decibel (dB) change. ä A decibel is a ratio between two intensities: 10 * log 10 (I 1 /I 2 ) ä 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 l Our perception of pitch is related (logarithmically) to changes in frequency ä Higher frequencies are perceived as higher pitches ä We can hear between 5 Hz and 20,000 Hz (20 kHz) ä A above middle C is 440 Hz

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

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

CompSci Nyquist Theorem l We need twice as many samples as the maximum frequency in order to represent (and recreate, later) the original sound. l The number of samples recorded per second is the sampling rate ä If we capture 8000 samples per second, the highest frequency we can capture is 4000 Hz That’s how phones work ä 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 l Call a friend on a phone and play some music over the phone ä How does it sound? ä Why does it work for voice but not for music?

CompSci Georgia Institute of Technology Playing a Sound l We can create a Sound object just as we created a Picture object ä Get a file name and save a reference to it –Pick a file that ends in.wav ä 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); ä Play the Sound play(sound1);

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

CompSci Georgia Institute of Technology Digitizing Sound in the Computer l Each sample is stored as a number (two bytes) l What’s the range of available combinations? ä 16 bits, 2 16 = 65,536 ä But we want both positive and negative values To indicate compressions and rarefactions. ä What if we use one bit to indicate positive (0) or negative (1)? ä That leaves us with 15 bits ä 15 bits, 2 15 = 32,768 ä 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

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

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

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

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

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

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

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

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

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

CompSci Georgia Institute of Technology Test Case 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. l Were Def Jeff’s actions within the limits of fair use? l Would he lose a lawsuit? l Were his actions ethical?