1 Revision

2 Multimedia Systems 1  Lecture 1 - The Physics of Sound  Lecture 2 - The Java Sound API  Lecture 3 - Input Transducers (Microphones)  Lecture 4 - Output Transducers (Speakers)  Lecture 5 - Manipulating Audio (A/D)  Lecture 6 - Manipulating Digital Audio (D/A)  Lecture 7 - Manipulating Digital Audio (Effects)  Lecture 8 - Storing Digital Audio (CD)  Lecture 9 - Digital Audio Storage Formats (Wav / MIDI)  Lecture 10 - Digital Audio Compression (Perceptual coding)  Lecture 11 - PC Audio (Sound cards)  Lecture 12 - Issues in Digital Audio (copyright)

3 Physics of Sound  Sound waves  Wavelength, Frequency  Bandwidth  Bass, Treble, Timbre  Amplitude, Decibels  Harmonics  Superposition, Fourier  Multiple channels

4 Input Transducers  Dynamic and Condensing microphones  Construction  Principles of operation  Advantages/ disadvantages  Pick-up patterns  Omnidirectional  Unidirectional  Bidirectional  Principles, advantages, disadvantages

5 Input Transducers  Proximity effect, frequency response  Balanced system  Principle of operation  Common mode rejection  Phantom Powering  Feedback

6 Output Transducers  Loudspeakers  Components and operation  Tweeter, Mid range and woofers  Frequency Response  Crossovers  Passive – low, mid and high pass  Active filter  Passive and active speakers

7 Output Transducers  Distortion  Intermodulation  Harmonic  Transient  Loudness  Enclosures  Infinite Baffle  Vented Enclosure

8 Manipulating Audio  The Digital domain  Advantages / disadvantages  Nyquist  Aliasing  Low pass filtering  Digital  Analogue  Oversampling

9 Manipulating Audio  Oversampling

10 Manipulating Audio  Quantization  Levels  Noise  Error/Accuracy  Dithering

11 Manipulating Audio  A to D Principal elements Multiplexer Processing (error correction) Dither generator Sample and Hold Anti- aliasing filter A to D Converter Sample and Hold Anti- aliasing filter A to D Converter Analogue input (L) Analogue input (R)

12 Manipulating Digital Audio  PCM  NRZ, NRZI, FM, PE  Error Correction  D to A Principal elements Demultiplexer Processin g (error correction) Reproduction demodulation Output sample and Hold Output lowpass filter D to A Converter Output sample and Hold Output lowpass filter D to A Converter

13 Manipulating Digital Audio  D/A conversion  Absolute linearity error  Differential linearity error  Sample and Hold  Low pass filtering  Oversampling

14 Manipulating Digital Audio  Effects  Delay  Echo  Reverb  Flanging  Pitch,Tempo  Amplitude envelope, dynamic range  Pan and Balance

15 Storing Digital Audio  Optical storage  Advantages/disadvantages  Audio CD  Frame structure and operation  Audio data  Sync word  Parity  Subcode 0.163mm 1 Frame Sync (24 bits) Sub code Data (96 bits) Parity (32 bits) Data (96 bits) Parity (32 bits) 8 bits P,Q,R,S,T,U,V,W Compact Disc

16 Storing Digital Audio  Audio CD  Eight to Fourteen Modulation Reasons Structure

17 Storing Digital Audio  CD-ROM Data Block  Structure  Why extra EDC/ECC  DAT  Mini Disc

18 Digital Audio Storage Formats  Wave, Au, Aiff  Descriptor  Format information  Data  MIDI  Advantages/ disadvantages  Message Format Status byte, Data byte  General MIDI  Sequencers

19 Digital Audio Compression  Psychoacoustics  Threshold of Hearing & Masking

20 Digital Audio Compression  Amplitude Masking  Critical Bands  Temporal Masking  Perceptual Coding  Conceptual operation  Joint Stereo Coding  MP3

21 PC Audio  Sound Card Components  Digital I/O  CD Analogue Audio Input  Line in/out  Digital Audio Extraction  Advantages/ disadvantages  Synthesis  FM  Wave table

22 Issues in Digital Audio  Intellectual Property  Copyright  Fair Use – Four factors  Exceptions  Sampling  Ownership  Licensing  Napster

23 Fin