Representing sound

Anotações:

• Learn more about this: https://www.bbc.co.uk/education/guides/zpfdwmn/revision/3 (basic level) https://teachwithict.weebly.com/binary-representation-of-sound.html (intermediate level) https://www.bbc.co.uk/education/guides/z7vc7ty/revision/1 (advanvced level)

1. Analogue Sound
   1. Vibration of the air
   2. Travels as sound waves
   3. Amplitude
      1. Constantly changing over time
      2. Can have any possible values between a minimum and a maximum
      3. Too much information: cannot be stored in a computer as it is
      4. The height of a sound wave. The higher is the amplitude, the louder is the sound.
   4. Frequency
      1. How fast the sound waves changes in a second. It is measured in Hertz (Hz). The higher is the sound frequency, the higher is the pitch.
2. Digital Sound
   1. A sound wave represented as binary numbers
   2. Can be processed by a computer
   3. Audio file
      1. WAV
         1. Type of high-quality sound file used in Windows systems
      2. AIFF
         1. Type of high-quality sound file used in Mac systems
      3. AAC
         1. Type of compressed, low-quality sound file used in mobile phones
      4. MP3
         1. Type of compressed, low-quality sound file used on any system
      5. A computer file that stores a digital sound
3. Sound digitization
   1. Amplitude is measured at regular intervals, not constantly
      1. Sampling rate
         1. The number of samples taken in one second. Measured in Hertz (Hz).
         2. The higher is the sampling rate, the better quality is the digital sound
         3. The higher is the sampling rate, the larger is the sound file size
         4. Typical values: 44.1KHz (44.1 thousand samples per second, CD quality)
         5. Typical values: 8 KHz (8 thousand samples per second, telehone quality)
      2. Sample
         1. A single measurement of amplitude
   2. Amplitude measurements are approximated, only a limited number of values, not all, are possible. Each sample is stored as a binary number
      1. Bit depth
         1. The number of bits used for each sample.
         2. The higher is the bit depth, the better quality is the digital sound
         3. The higher is the bit depth, the larger is the sound file size
         4. Typical values: 8 bits (256 possible values, low-quality)
         5. Typical values: 16 bits (65536 possible values, CD quality)
   3. The process of converting analogue sound into digital sound
   4. Bit rate
      1. The number of bits used for one second of digital sound. Can be calculated as: SamplingRate x BitDepth x NumnerOfChannels (1 channels is a 'mono' sound, 2 channels is a 'stereo' sound)