1.1.3(b): show understanding of the concept of MIDI files, JPEG files, MP3 and MP4 files:

MIDI:
Musical Instrument Digital Interface is a widely-used standard for interconnecting electronic musical instruments and computers. Its associated with the storage of music files. However, the MIDI files don’t contain any sound. This makes them much smaller than other music file types. MIDI uses 8 bit, asynchronous serial transmission, which means that there is a start bit and stop bit. A MIDI file consists of a list of commands instructing which note to play and how loud. MIDI has 16 channels.

JPEG:

When a photographic file is compressed, the size of the file is reduced. However, the quality of the image is sacrificed for this reduction of size. Once an image is compressed, a new file is created which replaces the original file.

Joint Photographic Experts Group will reduce raw bitmap image by a factor of 5 – 15 (depending on the quality of the image)

The file size of an image is determined by the number of pixels as well as the number of primary colours the image uses. Most images use three primary colours: red, green and blue.

The number of pixels of an image is calculated by the length x width.

e.g.: an image which is 1000 px by 2000px:

so, 1000 x 2000 = 2,000,000 px

so the file size of that image would be : 2,000,000 x 3 (3 because 3 primary colours)

= 6,000,000 bytes

=5859.38 kilobytes

=5.72 megabytes

e.g an image is 128 by 364 pixels:

= 128 x 364 = 46,592 px

è Calculate the size of the file:

=46,592 x 3(primary colours)

=139,776 bytes

= 139,776 / 1024 = 136.5 kilobytes

Calculate the size of the JPEG file when its reduced by a factor of 7:

136.5 / 7

= 19.5 kilobytes

MP3

Moving Pictures Experts Group-3

Uses audio compression technology to convert sound into a MP3 format. This reduces the size of a normal sound file by around 90% (so a factor of 10)

For example, an 80-megabyte sound file could be reduced to an 8 megabyte MP3 file.

This is done by removing sounds that humans can’t hear

(perceptual music shaping)

e.g: Music is to be stored on a CD. Each minute of music is worth 12 megabytes.

Calculate how much space the CD would need to store 3 tracks which are 3, 6 and 7 minutes long

=3+6+7 = 16 minutes

=16 * 12 = 192 megabytes

e.g: Calculate how much space the CD would now need (you may assume the file size is reduced by 90%)

192 x 0.1 = 19.2 megabytes

e.g: The CD has 800 megabytes of space. Calculate how many minutes can be stored on the CD

=800 / 12

=66.67 minutes

MP4

MP4 instead of just storing music, it can also store multimedia