1. Data representation – Sound.

2. Learning Objectives - Candidates should be able to:
(n) explain how sound can be sampled and stored in digital form
(o) explain how sampling intervals and other considerations affect the size of a sound file and quality of its playback.

3. Recap
How many colours could be represented per pixel in a 4 bit colour pallet
The more bits per pixel the greater the colour depth, better image quality
Resolution is the number of pixels per inch (PPI) or (DPI)
As we know, a bitmapped image when enlarge does not gain more pixel, these pixels are merely stretched

4. Definitions Type Definition Other Fact Analogue Continuously variable
Music
Speech
Activation Sensor
Digital
Binary pattern
Can be stored
Can be processed

5. When To Use Which? Analogue Playing Music Telephone Call Analogue
Music stored on USB Key
Fibre optic transmission
A song being edited in Audacity
Electricity along a copper wire
Analogue
Digital
Digital
Digital
Analogue

6. How do we store sound on computers?
Sample the sound at set intervals.
Max possible Value
Max possible Value
+128
+128
time
time
-127
-127
Min Possible Value
Min Possible Value

7. Analogue to Digital Conversions

8. Sampling
Sampling Resolution = The number of bits needed to store one sound sample
Sampling Rate = The frequency at which samples are taken
The bigger the sample interval the lower the sample rate
The height of the wave is sampled at regular
intervals
The height is represented by a code (011, 111, …)

9. What affects the quality / file size?
How often you take a sample…(sample rate)
44100 Hz
16000 Hz…
The Sample Resolution
How many bits you use for each sample
16 bits per sample gives 65,536 possible levels. (216)

10. Digital Mono Storage Requirement
16 bits per 44.1KHz
44100 sample X 2 /
1024
44100 Samples
Sec
16 Bits
Sample /
1 Byte
8 Bits /
1 Kb
1024 Bytes *
How Much Storage For A 5 Second Clip?
= 86.1 Kb/Sec
86.1 Kb/Sec * 5 Sec = Kb

11. Digital Stereo Storage Requirement
16 bits per 44.1KHz by 2 channels
44100 sample X 4 /
1024
1 Byte
8 Bits
1 Kb
1024 Bytes
44100 Samples
Sec
16 Bits * 2
Sample * * *
= Kb/Sec
How Much Storage For A 15 Second Clip?
Kb/Sec * 15 Sec = Kb

12. Limericks…
There was an old person from Fratton Who would go to church with his hat on. 'If I wake up,' he said, 'With a hat on my head, I will know that it hasn't been sat on.'
There was a young man from Dealing Who caught the bus for Ealing. It said on the door Don't spit on the floor So he jumped up and spat on the ceiling
There was an old man from Milan, Whose limericks never would scan. When told this was so, He said, 'yes, I know. 'But I always try to get as many syllables into the last line as I possibly can.'
There was an Old Man from Nantucket Who kept all his cash in a bucket. His daughter, called Nan, Ran away with a man, And as for the bucket, Nantucket

13. Activity…
Understanding the structure of a Limerick
Write your own to explain the file size of audio recordings.
You need to include the words sample rate and Sample frequency

14. Open Audactiy Plug headphones / mic in before you open application.
Once you have a Limerick
Using a Microphone provided record your Limerick
Start with the sample rate set to 44,100
Export the file
Repeat the exercise with the sample rate set to 16,000
Explain the difference in file size
Show your working.