data representation

• describe ADC process

  analogue signal sampled at regular time intervals. Voltage of signal at each sample point is measured. These measurements are coded into binary and stored.
• Nyquist's theorem:

  Sampling rate must be at least double the highest frequency found in the original sound
• explain how data is compressed by dictionary based compression:

  Substrings of original data are represented by single tokens. A dictionary is formed using the tokens as keys and substrings as entries. The compressed file will store the dictionary with the references to entries.
• features of bitmap graphics:

  • made up of pixels
  • colour bit depth - amount of bits per pixel
  • enlarging causes loss of quality
  • suited to photographs
• features of vector graphics:

  • made up of geometric shapes
  • can be scaled while preserving quality as objects can be mathematically reconstructed
  • suited to things like logos, not photographs
  • often smaller files than bitmap
• Nyquist's theorem:

  The sampling rate must be at least double the highest frequency of the original sound.
• sound resolution:

  Number of bits allocated to each sample
• How does MIDI store sound?

  As a series of event messages. These contain things like pitch, duration, volume
• Advs. of MIDI:

  • Can modify notes without rerecording entire piece
  • Wider range of instruments
  • Usually smaller file size than sampled audio
• Disadvs. of MIDI:

  • less realistic
  • doesn't store speech