1. Multimedia: Digitised Sound Data
Section 3

2. Sound in Multimedia Types: Voice Overs Special Effects
Sound can make multimedia presentations dynamic and interesting.
They can also be used to assist user.
Types:
Voice Overs
Special Effects
Musical Backdrops

3. Sound Capture Microphone: CD/DVD: Analogue Can be used for voice-overs
Digital
Capturing music files
Copyright laws may apply
If it comes from the real world how do we convert into digital? ADC

4. Sampling Frequency
Once an analogue signal is received it is chopped up and a sample is taken
The sampling frequency is the number of samples taken per second.
Samples of Sound Wave
Sound Wave

5. Sampling Frequency
Measurements (or samples) will be taken many times each second
The sampling rate for audio CD is 44.1kHZ means thousand samples per second.

6. Sampling Depth
This describes the number of bits which are taken in each sample
This will determine the dynamic range of the recording
An audio CD will have a sampling depth of 16bits (65536 levels)

7. Multimedia: Digitised Sound Data
Storage of Sound Data

8. RAW Uncompressed audio data
Sampled digital data which has not been processed further
The process of sampling he analogue signal and quantising depending on the strength of the signal (amplitude) is called Pulse Amplitude Modulation (PAM)
Quant – turning it into numbers

9. RAW
When data from PAM (Pulse Amplitude Modulation) is stored sequentially it is called Pulse Code Modulation (PCM)
PCM allows digital data to be transmitted over a network or to a sound card as it is easily decoded and used to construct the original sound as it is being received.

10. RIFF Resource Interchange File Format It is a container file
It can contain various types of data (e.g. video, bitmaps, sound, etc)
RIFF is a multimedia file format. The type of information stored is stated by the header.
Header – wave first part of the file

11. WAV File Wave files are RIFF files containing digitised sound data
They are commonly encoded using Adaptive Differential Pulse Code Modulation (ADPCM)
Often used in places such as digital telephone systems and minidisc players.

12. MP3 MPEG Audio Layer-3 (MP3) Uses lossy compression
Based on what humans hear best
Perceptual Audio Compression
Reduces RAW formats to around 10% of original size
3min of CD quality song = 30Mb
3min of MP3 = 3Mb
Quality is adjustable

13. File Size Vs Quality Sampling depth: Sampling frequency: Sound time:
increased sound depth
Greater range of values
Better sound quality and greater file size.
Sampling frequency:
The higher the sampling frequency, the better the sound quality, the greater the file size.
Sound time:
Longer track lasts the larger the file size
Affects file size but not quality.

14. Comparing Bitmap image files and digitised sound files
Each sample records data for a pixel
Bitmap: Resolution
Sound: Frequency
Bitmap: Number of bits for each sample/number of colours used
Colour depth
Sound: Number of bits determines number of signal levels that can be recorded
Sampling Depth

15. Multimedia: Digitised Sound Data
Storage of Sound Data