Representing Sound (Cambridge (CIE) O Level Computer Science)

Revision Note

Robert Hampton

Written by: Robert Hampton

Reviewed by: James Woodhouse

How Sound is Sampled & Stored

How is sound sampled & stored?

  • Measurements of the original sound wave are captured and stored as binary on secondary storage

  • Sound waves begin as analogue and for a computer system to understand them they must be converted into a digital form

  • This process is called Analogue to Digital conversion (A2D)

  • The process begins by measuring the amplitude of the analogue sound wave at a point in time, called samples

  • Each measurement (sample) generates a value which can be represented in binary and stored

  • Using the samples, a computer is able to create a digital version of the original analogue wave

  • The digital wave is stored on secondary storage and can be played back at any time by reversing the process

Digital wave represented on a graph on top of an analogue wave to show differences
  • In this example, the grey line represents the digital wave that has been created by taking samples of the original analogue wave

  • In order for the digital wave to look more like the analogue wave the sample rate and bit depth can be changed

Sample Rate & Sample Resolution

What is sample rate?

  • Sample rate is the amount of samples taken per second of the analogue wave

  • Samples are taken each second for the duration of the sound

  • The sample rate is measured in Hertz (Hz)

  • 1 Hertz is equal to 1 sample of the sound wave

Diagrams to show the differences between analogue, 8 bit and 16 bits digital waves

In this example you can see that the higher the sample rate, the closer to the original sound wave the digital version looks

Telephone, CD and DVD with sample rates
  • The sampling rate of a typical audio CD is 44.1kHz (44,100 Hertz or 44,100 samples per second)

  • Using the graphic above helps to answer the question, “Why does telephone hold music sound so bad?

What is sample resolution?

  • Sample resolution is the number of bits stored per sample of sound

  • Sample resolution is closely related to the colour depth of a bitmap image, they measure the same thing in different contexts

What effect do sample rate and sample resolution have?

 

 

Sample rate

Sample resolution

High

Low

High

Low

Playback quality

File size

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Robert Hampton

Author: Robert Hampton

Expertise: Computer Science Content Creator

Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.

James Woodhouse

Author: James Woodhouse

Expertise: Computer Science

James graduated from the University of Sunderland with a degree in ICT and Computing education. He has over 14 years of experience both teaching and leading in Computer Science, specialising in teaching GCSE and A-level. James has held various leadership roles, including Head of Computer Science and coordinator positions for Key Stage 3 and Key Stage 4. James has a keen interest in networking security and technologies aimed at preventing security breaches.