CIE A Level Physics (9702) 2019-2021

Revision Notes

20.2.1 Digital & Analogue Signals

Digital v Analogue Form

  • An analogue signal consists of varying frequency or amplitude
    • Telephone transmission and broadcasting uses analogue technology
  • A digital signal is generated and processed in two states:
    • 1 or 0 (high or low states respectively)
  • Digital technology stores and transmits data in the form of 1s and 0s, just like in mobile phones or programming in computer

Analogue v digital, downloadable AS & A Level Physics revision notes

Analogue v digital signal

  • The key advantages of transmission of data in digital form compared to analogue are:
    • The signal can be regenerated so there is minimal noise
    • Extra data can be added so that the signal can be checked for errors

Digital Transmission of Speech or Music

  • Signals for speech or music are made up of varying frequencies
  • In order to make out words clearly, the signal needs to be transmitted with as little interference as possible
  • The signal goes through a conversion before transmission and after the reception
  • Before transmission the conversion is:
    • Analogue-to-digital conversion (ADC)
  • After reception:
    • Digital-to-analogue conversion (DAC)

Sampling Rate

  • A sample is a digital representation of an analogue signal
  • When an analogue signal is converted into a digital signal it becomes encoded into ‘bits’ (short for binary digit)
  • The sample size is defined as:

The number of digital bits used to describe each sample

  • The sampling rate is defined as:

How many samples per second a digital audio system uses to record an audio signal

  • Sampling rate is measured in Hertz (Hz)
  • Sampling rates for music are in the region of 40 – 50 kHz as this covers the range of human hearing
  • Step height is a measure of the number of bits between the analogue and digital signal
  • Increasing the number of bits in each sample improves the reproduction of an input signal since the step height is reduced

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