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A Media Computation Cookbook

A Media Computation Cookbook. Manipulating Images and Sounds for Use in Alice Part 1: Image Manipulations Part 2: Advanced Image Manipulations, e.g., changing colors in an area Part 3: Chromakey for digital video effects Part 4: Manipulated Alice images Part 5: Sound manipulations

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A Media Computation Cookbook

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  1. A Media Computation Cookbook Manipulating Images and Sounds for Use in Alice Part 1: Image Manipulations Part 2: Advanced Image Manipulations, e.g., changing colors in an area Part 3: Chromakey for digital video effects Part 4: Manipulated Alice images Part 5: Sound manipulations Part 6: Manipulated sounds in Alice

  2. How sound works:Acoustics, the physics of sound • Sounds are waves of air pressure • 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 • The amplitude of the sound determines the volume. • The frequency of the sound determines the

  3. Live demos here! • See real sounds, and real musical instruments

  4. Digitizing Sound: How do we get that into numbers? • We take the height of the wave at regular intervals. • That’s called the Sampling Rate. • Each sample is between -32768 and +32767 • How many samples do we need? • Nyquist Theorem: • We need twice as many samples as the maximum frequency in the sound in order to represent (and recreate, later) the original sound. 500, 1000, 1250, 1312, 1475,… • Phones capture 8,000 samples per second (8 Kilohertz, Khz). • Highest sound humans can hear is 22 Khz. • CD quality sound is 44,100 samples per second

  5. Loading sounds from WAV files >>> sound = makeSound(pickAFile()) >>> explore(sound)

  6. Where to get sounds? • Any .WAV file from anywhere on the Internet. • Speech.zip on http://coweb.cc.gatech.edu/mediaComp-teach/43 • Expand it and put it in your media folder. • Musicsounds.zip on same page.

  7. How do you increase volume? >>> increaseVolume(sound) >>> explore(sound) def increaseVolume(sound): for s in getSamples(sound): value = getSampleValue(s) setSampleValue(s, ???)

  8. Code for sounds • makeSound(file) – makes a sound • explore(sound) – look at and plaly sounds • getSamples(sound) – returns a list of samples. • getSampleValue(sample)/setSampleValue(sample, – gets and changes samples • getSampleValueAt(sound,index)/setSampleValueAt(sound,index,value) • getLength(sound) – returns number of samples in sound. • makeEmptySound(len) – makes a new sound with # of samples. • writeSoundTo(sound, filename) – writes out the sound (end filename with “.wav”)

  9. What if you set all the samples as big as you can? def maximize(sound): for s in getSamples(sound): value = getSampleValue(s) if value >= 0: setSampleValue(s,32768) if value < 0: setSampleValue(s,-32767) >>> maximize(sound) >>> explore(sound) Can you make out what sound this is?!?

  10. Splicing sounds together >>> setMediaPath() 'D:\\WorkingDocs-Copy\\Glitch-MediaComp\\musicsounds\\' >>> guzdial = makeSound(getMediaPath("guzdial.wav")) >>> issnd = makeSound(getMediaPath("is.wav")) >>> inside = makeSound(getMediaPath("inside.wav")) >>> guzdialis = makeSplice(guzdial, issnd) >>> play(guzdialis) >>> guzdialisinside = makeSplice(guzdialis,inside) >>> explore(guzdialisinside)

  11. Code for makeSplice def makeSplice(sound1,sound2): newSound = makeEmptySound(getLength(sound1)+getLength(sound2)) index = 0 for s in getSamples(sound1): setSampleValueAt(newSound,index,getSampleValue(s)) index = index + 1 for s in getSamples(sound2): setSampleValueAt(newSound,index,getSampleValue(s)) index = index + 1 return newSound

  12. Mixing sounds to make a chord def makeChord(): notec = makeSound(getMediaPath("brass-c4.wav")) notee = makeSound(getMediaPath("brass-e4.wav")) noteg = makeSound(getMediaPath("brass-g4.wav")) mixce = makeMix(notec,notee) play(mixce) mixceg = makeMix(mixce,noteg) play(mixceg) return mixceg >>> chord=makeChord() >>> explore(chord)

  13. Mixing sounds in different amounts def makeChord(): notec = makeSound(getMediaPath("brass-c4.wav")) notee = makeSound(getMediaPath("brass-e4.wav")) noteg = makeSound(getMediaPath("brass-g4.wav")) mixce = makeMix(notec,notee) play(mixce) mixceg = makeMix(mixce,noteg,0.75,0.25) play(mixceg) return(mixceg) >>> chord=makeChord() >>> explore(chord)

  14. Making an Echo >>> always = makeSound(getMediaPath(“always.wav")) >>> explore(always) >>> echo = makeEcho(always) >>> explore(echo)

  15. How the echo code works def makeEcho(sound,spacing=10000,repeat=5): newSound = makeEmptySound(getLength(sound)+spacing*repeat) #Put the initial sound in index = 0 for s in getSamples(sound): setSampleValueAt(newSound,index,getSampleValue(s)) index = index + 1 #Now put the echoes in for echoes in range(1,repeat): echoSound = makeEmptySound(getLength(sound)+spacing*repeat) index = echoes * spacing for s in getSamples(sound): setSampleValueAt(echoSound,index,getSampleValue(s)) index = index + 1 newSound = makeMix(newSound,echoSound,0.9,0.1) return newSound

  16. Grabbing part of a sound >>> this = makeSound(getMediaPath("thisisatest.wav")) >>> explore(this) >>> testSound = makePartSound(this,47000,58100) >>> explore(testSound)

  17. Code for grabbing part of a sound def makePartSound(sound,start,finish): newSound = makeEmptySound(finish+start) index = 0 for src in range(start,finish): value = getSampleValueAt(sound,src) setSampleValueAt(newSound,index,value) index = index + 1 return newSound

  18. Making sounds lower or higher • >>> shorter = makeScaleSound(this,0.5) • >>> explore(shorter) • >>> longer = makeScaleSound(this,2.0) • >>> explore(longer) • >>> same = makeScaleSound(this,1.0)

  19. How we make sounds higher or lower def makeScaleSound(sound,factor): newLength = int(getLength(sound)*factor) newSound = makeEmptySound(newLength) src = 0 for index in range(0,newLength): value = getSampleValueAt(sound,int(src)) setSampleValueAt(newSound,index,value) src = src + 1.0/factor return(newSound)

  20. Scaling is always the same def makeScaleSound(sound,factor): newLength = int(getLength(sound)*factor) newSound = makeEmptySound(newLength) src = 0 for index in range(0,newLength): value = getSampleValueAt(sound,int(src)) setSampleValueAt(newSound,index,value) src = src + 1.0/factor return(newSound) def scale(picture,factor): newHeight = int(factor*getHeight(picture))+1 newWidth = int(factor*getWidth(picture))+1 returnPic = makeEmptyPicture(int(newWidth),int(newHeight)) sx = 0 for tx in range(0,newWidth): sy = 0 for ty in range(0,newHeight): if (int(sx) < getWidth(picture)) and (int(sy) < getHeight(picture)): sp = getPixel(picture,int(sx),int(sy)) tp = getPixel(returnPic,tx,ty) setColor(tp,getColor(sp)) sy = sy + (1/factor) sx = sx + (1/factor) return returnPic

  21. Try it! • Make a function to decrease volume • Make a sentence by splicing words together, or make a song by splicing notes in a series. • Make a recording of yourself saying something, then make it ECHO…

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