Data Representation: Sound

Hearing Aid (Microphone)

Light Sensor

Heat Sensor

Question: What do they all have in common?

Lesson Objectives All Most Some We are learning today: The basic concept of analogue / digital data How computers store data about sound, temperature and light. What is meant by the term “Bit Sampling” What is meant by the term “Bit Resolution” What is meant by the term “Bit Rate” How the bit sampling / bit rate affect file sizes All Most Some

The basic concept of analogue / digital data Digital signals are discrete (not continuous) They are either OFF or ON In binary terms 0 or 1 Analogue signals continuous (infinite possibilities) Affected by noise The basic concept of analogue / digital data

What does it mean by continuous? Vinyl Record CD The basic concept of analogue / digital data

The basic concept of analogue / digital data Digital vs Analogue The basic concept of analogue / digital data

Sample Rate The number of samples of sound taken by a computer, which represents sound digitally, in a second. What is meant by the term “Sample Rate”

Sample Rate CD’s currently have a sample rate of 44100 Hhz or 44khz. Which means the sound is sampled at 44 100 times a second. What is meant by the term “Sample Rate”

Sample Rate What is meant by the term “Sample Rate” Reading Volt .10 sec -1 .25 sec 1 .40 sec 7 .55 sec 6 .70 sec 5 .85 sec 2 1.00 sec Signed Binary 10000001 00000001 00000111 00000110 00000101 00000010 What is meant by the term “Sample Rate”

A single square on an image is a pixel.

Bit / Colour Depth Any black / white images have a colour / bit depth of 1-bit. The pixel is either white or black.

These are 8 bit /16 bit images. Bit / Colour Depth These are 8 bit /16 bit images. This means a pixel can choose between 0-255 or 0-65535 colours.

Bit / Colour Depth To store true colour (photo quality) you need at least 24bit (from 0 – 16 million colours).

Each pixel in this image stores the colour code: 9F7FA8 100111110111111110101000

What is the sample resolution this? Remember: I used 1 ‘I’ for each sample. The number of bits assigned to each sample. What is the sample resolution this? Reading Volt .10 sec -1 .25 sec 1 .40 sec 7 .55 sec 6 .70 sec 5 .85 sec 2 1.00 sec 1.15 sec -3 Signed Binary 10000001 00000001 00000111 00000110 00000101 00000010 10000011 8 bits What is meant by the term “Sample Resolution”

Bit Rate Bit Rate – The number of bits required to store 1 second of sound. This is then played back at Mbps (Megabits per second) What is meant by the term “Bit Rate”

What is the bit rate for this? Bit Rate – The number of bits required to store 1 second of sound. This is then played back at Mbps (Megabits per second) Reading Volt .10 sec -1 .25 sec 1 .40 sec 7 .55 sec 6 .70 sec 5 .85 sec 2 1.00 sec 1.15 sec -3 Signed Binary 10000001 00000001 00000111 00000110 00000101 00000010 10000011 What is the bit rate for this? 56Mbps What is meant by the term “Bit Rate”

Recap Sample Rate – No of samples per second Sample Resolution – No of bits assigned to each sample Bit Rate – Amount of bits for 1 second of sound What is meant by the term “Bit Rate”

File Size Sample Rate = 8000Hz Sample Resolution = 16 bit File Size = Sample Rate * Sample Resolution * Length of sound Sample Rate = 8000Hz Sample Resolution = 16 bit Length of Sound = 30 seconds 8000 * 16 * 30 = 3 840 000 bits or 480 000 bytes How to calculate a file size

How can the different rate effect the sound quality. 8khz 22khz 44khz How the bit sampling / bit rate affect file sizes.