Chapter 2 Communication and Internet Technologies

Bit depth

OBJECTIVES:

• Show understanding that sound (music), pictures, video, text and numbers are stored in different formats

• 16-bit resolution means each sample can be any binary value between 0000 0000 0000 0000 and 1111 1111 1111 1111.
• 24 bit means the maximum binary number is 1111 1111 1111 1111 1111 1111 which creates 16,777,215 possible values.

Bit rate

OBJECTIVES:

• Show understanding that sound (music), pictures, video, text and numbers are stored in different formats

• The bit rate of a file tells us how many bits of data are processed every second.
• Bit rates are usually measured in kilobits per second (kbps).

Calculating bit rate

• The bit rate is calculated using the formula:

Bit Rate = Frequency × bit depth × channels

• Size of a file is calculated using the formula:

Size = Bit Rate × Time

Bit rate

OBJECTIVES:

• Show understanding that sound (music), pictures, video, text and numbers are stored in different formats

A typical, uncompressed high-quality audio file has a sample rate of 44,100 samples per second, a bit depth of 16 bits per sample and 2 channels of stereo audio. The bit rate for this file would be:

• 44,100 samples per second × 16 bits per sample × 2 channels = 1,411,200 bits per second (or 1,411.2 kbps)

A four-minute (240 second) song at this bit rate would create a file size of:

• 1,411,200 × 240 = 338,688,000 bits (or 40.37 megabytes)

SUMMARY

• Computers convert text, images and sound into binary to process and store.
• In summary, sample rate is the number of audio samples recorded per unit of time and bit depth measures how precisely the samples were encoded. Finally, the bit rate is the amount of bits that are recorded per unit of time.

KEY TERMS

• Analogue – the stream of data used in the ‘real world’, e.g. a sound wave
• Digital – data that is represented in 1s and 0s (binary)
• Sampling – reading the height of a sound wave at a set interval; this is converted into a binary number

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