sound

    Cards (9)

    • analogue vs digital signals
      'real world' sound is a combination of different frequencies, and is analogue - meaning the signals are a continuous wave and have an infinite range of values.

      Compared to digital which is 'discrete' (set values).

      sound is processed digitally by computers. and the two types of signal can be converted between.
    • sound signal conversion
      analogue sound samples are recorded via an amplifier.
      the samples are quantised to measure wave height
      the values are translated into integer form
      these values are converted and stored digitally as binary

      (the steps are reversed for digital to analogue)
    • sound sampling
      analogue signals are measured (for amplitude/voltage) at regular time periods.

      sampling rate = number of samples taken a second and it is measured in HZ

      (the frequency of sampling per second affects the level of data in the digital representation)

      increase in frequency = increase in accuracy = increase in file size
    • sound resolution
      resolution = number of bits (audio bit depth) used to record each sample.
      the more bits per sample, the higher the accuracy, the larger the file size
    • sound file size
      file size = sample rate * resolution * length (seconds)
      stereo sound has two channels for the left and right so the file size is doubled
    • limitations of sound sampling
      -> there is a limit on the lowest sample rate that can be used on a recording and still produce an accurate digitalised sound.
      ->the sound must be sampled at *2 the frequency of the highest frequency it contains in order to replicate the original accurately

      fs > 2f max = Nyquist's theorem
    • human hearing
      human hearing ranges from 20Hz to 22kHz for most people, but this deteriorates with age and our ears can be damaged by prolonged exposure to high frequency or high amplitude sounds

      (CD's use 44.11 KHz)
    • MIDI's
      -> standard Musical Instrument Digital Interface
      they create sound as requested from instruments or software by following instructions.
      They are synthesised instead of live recordings.
      pros: there is no need for the full signal to be transmitted = reduced amount of data transfer = increased efficiency
      cons: the sound is synthesised so may be less realistic (it can be altered digitally taking away from the authenticity)
    • uses of MIDI's
      sound processors - allow the linking of several instruments or computers.

      ->can produce timed sequence of event messages
      ->the tempo and pitch can be altered and synchronised as well as the volume being easily altered.

      (different sounds can be made louder or quieter, which is useful in music when mixing vocals and instruments together)
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