Representing sound

Representing sound

1. Analogue Sound

   • Vibration of the air
   • Travels as sound waves
   • Amplitude
     • Constantly changing over time
     • Can have any possible values between a minimum and a maximum
     • Too much information: cannot be stored in a computer as it is
     • The height of a sound wave. The higher is the amplitude, the louder is the sound.
   • Frequency
     • 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

   • A sound wave represented as binary numbers
   • Can be processed by a computer
   • Audio file
     • WAV
       • Type of high-quality sound file used in Windows systems
     • AIFF
       • Type of high-quality sound file used in Mac systems
     • AAC
       • Type of compressed, low-quality sound file used in mobile phones
     • MP3
       • Type of compressed, low-quality sound file used on any system
     • A computer file that stores a digital sound

3. Sound digitization

   • Amplitude is measured at regular intervals, not constantly
     • Sampling rate
       • The number of samples taken in one second. Measured in Hertz (Hz).
       • The higher is the sampling rate, the better quality is the digital sound
       • The higher is the sampling rate, the larger is the sound file size
       • Typical values: 44.1KHz (44.1 thousand samples per second, CD quality)
       • Typical values: 8 KHz (8 thousand samples per second, telehone quality)
     • Sample
       • A single measurement of amplitude
   • Amplitude measurements are approximated, only a limited number of values, not all, are possible. Each sample is stored as a binary number
     • Bit depth
       • The number of bits used for each sample.
       • The higher is the bit depth, the better quality is the digital sound
       • The higher is the bit depth, the larger is the sound file size
       • Typical values: 8 bits (256 possible values, low-quality)
       • Typical values: 16 bits (65536 possible values, CD quality)
   • The process of converting analogue sound into digital sound
   • Bit rate
     • 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)