Introduction

• Odds are you use it every day, but what is it?

Audio

• Computers are good at recording, playing back, and generating audio

• Uses different file formats

  • File formats are just a way of storing 0s and 1s on disk so that certain software knows how to interpret it

• MIDI

  • Way of storing musical notes for certain songs
  • Can do this for different instruments
    • Programs can render the notes for these instruments

• GarageBand

  • Included with macOS

  

  • This is the Star Wars theme in MIDI
    • Doesn’t sound quite as good as the actual version
    • The computer synthesizes the notes
      • Not an actual recording
      • The computer interprets notes in the MIDI file

• MIDI is common in the digital workspace among musicians who wish to share music.

• Humans typically like to hear music performed and recorded by humans

  • File formats for recorded music include:
    • AAC
    • MIDI
    • MP3
    • WAV

• WAV is an early sound format, but still used

  • Uncompressed data storage allows high-quality

• MP3

  • File format for audio that uses compression
    • Significantly reduce how many bits are necessary to store a song
    • Discards 0s and 1s that humans can’t necessarily hear
      • True audiophiles may disagree
    • The trade-off between optimizing storage space and sacrificing quality
    • This compression is said to be lossy
      • Losing the quality in the compression process

• AAC

  • Similar to MP3
  • May see when you download a song from iTunes

• Streaming services such as Spotify don’t transfer a file to you but rather stream bits of information to you

• How do we think about the quality of these formats?

  • Sampling frequency
    • Number of times per second we take a digital snapshot of what a person would hear
  • Bit depth
    • The number of bits used for these individual snapshots
  • Sampling frequency x bit depth = number of bits necessary to store one second of music
  • Audio file formats allow you to modify what these parameters are

Graphics

• A graphic, what we see with multimedia, is just a bunch of pixels both horizontal and vertical

  • All file formats are rectangular, though transparent pixels can make images look to take on other shapes

  • In the simplest form, each of the dots or pixels is a bunch of 0s and 1s

    

  • To create a file format, we just need to determine a mapping

• This image is only black and white, so how to represent colour?

RGB

• RGB stands for Red Green Blue
  • With information giving an amount of red, an amount of green, and an amount of blue, you can tell a computer how to colourize pixels
  • None of the colours yields a black pixel
  • All of the colours yield a white pixel
  • In between these two options is where we get all sorts of colours
• Consider the three bytes: 11111111 00000000 00000000
  • If we interpret these bytes to represent colours, it appears we want all of the red, none of the green, and none of the blue
  • These 24 bits (3 bytes = 3 x 8 bits = 24 bits) represent the color we know as red!
    • If a computer wanted to represent this colour, it would store these 24 bits