memory and storage

• Compression


  Making a file's size smaller
• Benefits of compression


  • Files take up less storage space
  • Files can be transferred quicker
  • Files can be read from or written to quicker
• Lossy compression


  Uses an algorithm to analyse a file and remove data that cannot be heard or seen by humans
• Lossless compression


  Reduces the size of a file without permanently removing any data, so the file is returned to its original form when decompressed
• Lossy compression


  Removes data permanently, so the file can never return to its original form
• Lossy compression used with


  • Images
  • Audio
  • Video
• Lossless compression


  File is usually larger than a file compressed with lossy compression because no data has been permanently removed
• Lossless compression used with


  • Executable files (e.g. programs and games)
  • Word documents
• Lossy compression


  1. Analyse file

  2. Remove data that cannot be heard or seen by humans

  3. Further remove data that humans can see/hear

  4. Reduces file size
• Lossy compression removes data permanently
• Lossy compression is often used with images, audio and video to reduce file size
• Lossless compression reduces file size without permanently removing any data, so the file is returned to its original form when decompressed
• Lossless compression is used with files that would not work if data was removed, e.g. executable files and word documents
• Computers work in binary. All data must be converted into binary in order for a computer to process it. Sound is no exception.
• How computers process and represent sound


  1. Sound is captured by a microphone

  2. Converted into a digital signal by an analogue-to-digital converter

  3. Recorded as samples at regular time intervals
• Sample rate


  The number of samples recorded in any given period of time
• Higher sample rate


  Closer the recorded signal is to the original
• Sample rate is measured in hertz
• Higher sample rate


  Larger the resulting file
• Audio files are usually recorded at 44.1 kilohertz
• Bit depth


  The number of bits used to record each sample
• Higher bit depth


  More accurately a sound can be recorded
• Higher bit depth


  Larger the file size
• Bit rate


  A measure of how much data is processed for each second of sound
• Higher bit rate


  Better quality of the recorded sound
• Computers work in binary. All data must be converted into binary in order for a computer to process it. Sound is no exception.
• How computers process and represent sound


  1. Sound is captured by a microphone

  2. Converted into a digital signal by an analogue-to-digital converter

  3. Recorded as samples at regular time intervals
• Sample rate


  The number of samples recorded in any given period of time
• Higher sample rate


  Closer the recorded signal is to the original
• Sample rate is measured in hertz
• Higher sample rate


  Larger the resulting file
• Audio files are usually recorded at 44.1 kilohertz
• Bit depth


  The number of bits used to record each sample
• Higher bit depth


  More accurately a sound can be recorded
• Higher bit depth


  Larger the file size
• Bit rate


  A measure of how much data is processed for each second of sound
• Higher bit rate


  Better quality of the recorded sound
• Binary numbers are multiplied and divided through a process called shifting.

  Multiplication

  To multiply a number, a binary shift moves all the digits in the binary number along to the left and fills the gaps after the shift with 0:

  • to multiply by two, all digits shift one place to the left
  • to multiply by four, all digits shift two places to the left
  • to multiply by eight, all digits shift three places to the left
  • and so on