Binary Representation of Sound
Candidates should be able to:
- explain how sound can be sampled and stored in digital form
- explain how sampling intervals and other considerations affect the size of a sound file and the quality of its playback.
Sound travels in the form of a wave:
Amplitude controls how loud the sound is and the frequency controls the pitch. Example:
How is sound represented in binary?
Sound waves are analogue and therefore they need to be converted into binary in order for a computer to be able to process them. To do this, the computer must convert the waveform into a numerical representation so that the waveform can be stored digitally. For this, we use an Analogue-to-Digital Convertor (ADC).
An ADC works by taking samples of the sound wave at regular intervals:
Sound waves are analogue and therefore they need to be converted into binary in order for a computer to be able to process them. To do this, the computer must convert the waveform into a numerical representation so that the waveform can be stored digitally. For this, we use an Analogue-to-Digital Convertor (ADC).
An ADC works by taking samples of the sound wave at regular intervals:
The quality and size of the file is affected by two factors - sample rate and bit rate.
The sample rate refers to the number of samples taken every second and that the greater the frequency of the samples, the better the sound quality.
The bit rate refers to the number of bits used to store each sample and that the more bits that are sampled, the better the accuracy of the file but also the greater the file size.
The sample rate refers to the number of samples taken every second and that the greater the frequency of the samples, the better the sound quality.
The bit rate refers to the number of bits used to store each sample and that the more bits that are sampled, the better the accuracy of the file but also the greater the file size.
Below are some samples taken from an mp3 using Audacity.
Useful Resources:
PWNICT - Excellent PowerPoint presentation from PWNICT – Computing Resources explaining how sound is stored on a computer - Click on 2.1.4 representation of data --> Lesson 5 Sound in Binary
Classzone – Frequency / Amplitude simulator
Binary representation of sound worksheet – Courtesy of Emma Partridge (via CAS). Download the worksheet here: http://community.computingatschool.org.uk/resources/1035
Extract from the CHRISTMAS LECTURES 2008: Chris Bishop - The Ghost in the Machine showing how sound is stored on a computer - Skip to 13:40.
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