Binary!Objectives

• How sound is stored in digital format• What is meant by “sample interval” and how it

affects quality• The trade off between file size and quality.

Sample Binary sound file

• Binary numbers. • Metadata tells computer the type of file it is

(picture, or sound or video etc)

What is sound?

• Sound is measured in ‘cycles per second’ or Hertz (Frequency of sound -aka PITCH)

• There is also a loudness of sound – (The height of the wave aka AMPLITUDE)

What is sound?

• If air moving slowly – LOW PITCHED BASS. You can hear vibration to 20 cycles per second (20Hz) Example

• If air moving quickly –HIGH PITCHED TREBLE. You can hear up to 20,000 cycles per second (20kHz) Example

• Most sound is a mixture of different frequencies

Binarysound

Watch digital juice video on sampling rates.

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Binarysound waves 101

Sound travels as a wave. The amplitude of the wave controls how loud the sound is. The frequency controls the pitch.

Binarysound waves 101

The image above shows how a wave changes to produce different sounds

Image from scienceaid.co.uk

Binarysound waves 101

Sampling is a method of converting an analogue sound into a digital file containing binary numbers. Sound will be sampled at certain points along the wave. These are represented by the bars. After sampling we are left with a digital version of the sound.

BinaryHigher sampling rate

By doubling the sample rate we can represent the original sound wave much more closely. Increasing the sample rate will improve the quality of the sound file.

BinaryHigher sampling rate

The lower sample rate will create a crackly sound. Click on the speakers to hear the difference.

LOW SAMPLE

RATE

HIGH SAMPLERATE

BinaryQuality Vs file size

Each sample for a digital file takes up space. The more samples you have the higher the file size.

8000 Mhz file size was 2.1 MB (8000 samples per second)44100 Mhz file size was 11.5 MB (44100 samples per second)

The difference between file size and quality is very closely related. Ever noticed that sound on internet sites is poor? This is to help reduce the amount of time it will take to download.

Note – sample rate is sometimes referred to as bitrate.

BinaryActivity

Explain, in your revision PowerPoint, what is meant by sampling rate.

Also make notes on the relationship between file size and sample rate.