3_3_7 Representing Sound

You should be able to:

Understand that sound is analogue and that it must be converted to a digital form for storage and processing in a computer.
Understand that sound waves are sampled to create the digital version of sound.
Describe the digital representation of sound in terms of:

•• sampling rate

•• sample resolution

Calculate sound file sizes based on the sampling rate and the sample resolution.

REVISE:

The Basics

The basics are covered here: 8_1_4. Re-visit the page before moving on.

Resolution of Sound Files

The resolution of a sound file is connected to the number of slices that are made across the wave. If you take a look at this diagram it shows 16 horizontal slices. This means that there are 16 possible sounds that can be recorded. Because it is 16, we need 4 bits to represent each sound. These are shown on the left hand side of the chart.

The 16 slices measure the amplitude of the wave. The binary number recorded will be the one that is closest to the slice.

Calculating File Sizes

We know THREE things about our sound files to help us calculate the file size:

The bit rate / amplitude resolution (number of slices)
The sample rate / frequency (number of samples per second)
The length of the recording in seconds.

To calculate the number of bits required to store a sound file you would need to do this:

file size = (bit rate x sample rate x (minutes x 60))

e.g.

A 4-bit sound file with a frequency of 100hz that is 2 minutes long would be calculated like this:

4 x 100 x (2 x 60)

48000 bits or 6000 bytes or 6 kilobytes

TEST:

Download and print the test paper here: https://drive.google.com/open?id=0B5fLtQ0Xgr2PcGw0ZzNsS1VxSVE
Try the mock test yourself.
Use the 3.3.7 Walking Talking Mock below to guide you through answering the questions.

SOURCE RECOGNITION - PLEASE NOTE: The examination examples used in these walking talking mocks are samples from AQA from their non-confidential section of the public site. They also contain questions designed by TeachIT for AQA as part of the publicly available lesson materials.

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