1 Multimedia Systems 1 Dr Paul Newbury School of Engineering and Information Technology ENGG II - 3A11 Ext: 2615

2 Introduction  Audio Systems  The Physics of Sound  Java Sound API  Input Transducers  Output Transducers  Manipulating Audio  Manipulating Digital Audio  Storing Digital Audio  Digital Audio Formats  PC Audio  Audio Issues

3 Course Aims  ‘The course aims to give the student a broad introduction to audio systems and in particular digital audio’  The course covers the principles of audio capture manipulation and output using a computer based system

4 Course Objectives  ‘The student will understand the components and processes necessary to capture, manipulate and output audio. Along with an understanding of the wider issues involved with audio production and distribution’  They will be required to understand the principles of audio processing, the need for, and the main features of audio systems

5 Structure  Three single lectures per week:  Monday AS2  Tuesday AS2  Friday9.15 AS2  One, 2 hour lab per week  See lab timetable  One problem sheet per week  Fragments of exam style questions  To be handed in to the post box in the photocopier room by the following Friday

6 Course Web Page  All support materials for this course are available at:  This includes  All Lecture slides in.pdf and.ppt format  All Problem sheets in.doc and.pdf format  All Lab sheets in.html.doc and.pdf format  Links to support information on particular topics.

7 Lab Work  Two lab activities  Cool Edit 2000  Java Sound API

8 Course Assessment  Unseen exam 70%  Lab work 30% (Cool Edit and Java Sound API)

9 Reading Material  Look at the web pages for useful links.  Books:  Principles of Digital Audio, 4 th edition Ken C. Pohlmann McGraw-Hill (2000) This is a non-introductory text which covers the whole course. Only worth considering if you wish to find out more detail about the topics covered in the course

10 Introduction Physics of Sound

11 Acoustics  Study of sound  Generation  Transmission  Reception  Sound is the rapid change in air pressure  Speed at which air moves (and thus the sound travelling through it) depends on its density

12 Sound Waves

13 Sound Waves

14  The distance that sound travels through one complete cycle of pressure change  The time this takes is know as the period of the wave and is the reciprocal of frequency  Wavelength v = Velocity of sound (344m/s) f = frequency  20KHz =16.5mm  20Hz = 16.5 meters Wavelength

15 Frequency  The number of vibration cycles that pass a particular point each second  Measured in Hertz (Hz) cycles per second  The pitch of a sound is dependant on its frequency  Human ear can hear between 20Hz –20KHz (bandwidth)  Low frequency – Bass  High frequency – Treble

16 Bandwidth  The difference between the maximum rate of oscillation (or highest frequency) and the minimum rate of oscillation (or lowest frequency) of the sine waves making up the signal is known as the bandwidth of the signal

17 Bandwidth  Telephone bandwidth approx 400Hz to 3.4KHz  Voice on a telephone  Normal voice

18 Bass  Long wavelengths (middle bass 3 meters)  Easily bend around objects  Human hearing is not directionally sensitive to low frequency sound  A single low frequency speaker (subwoofer) can be used

19 Treble  Short wavelength (centimetres)  Easily blocked or reflected by objects  Human hearing is very sensitive to location

20 Timbre  Listening to a flute, violin or tuning fork each producing the same note (pitch) we can distinguish between them  It is the number of overtones (harmonic or not) and their relative amplitudes that determine timbre

21 Amplitude  Strength or power of the sound  Describes the sound pressure displacement above and below the equilibrium atmospheric level  The amplitude of sound travelling through air is usually expressed as sound pressure level SPL  Sound pressure is very small Threshold of hearing microbar Human ears have a large dynamic range

22 Decibels  A Bel is the relationship between two powers (ratio) expressed as a logarithm  Sound source P 1 = 1W  Sound source P 2 = 1mW  Ratio 1,000:1 or 3B or 30dB  Approximately coincides with the way we hear sounds

23 Decibels  In acoustic measurements the reference level is often set to the threshold of hearing W/m 2  Thus the intensity level of a band producing 10W/m 2   130 dB SPL(sound pressure level)

24 Harmonics

25 Harmonics  Fundamental Frequency

26 Superposition

27 Fourier  Any waveform can be decomposed into harmonic components.

28 Multiple Sound Channels  Stereo – the use of two separate sound signals to produces the effect that sound is coming from a spatial position between the two speakers  Binaural - uses special microphones placed inside a dummy head to make a recording  Quadraphonic – four channels, two front, two back  Surround sound – multiple speakers (e.g. 5.1)

29 Fin