1. BPC: Art and Computation – Summer 2007 Digital Media – Audio, part 2 Robert Putnam putnam@bu.edu

2. BPC: Art and Computation – Summer 20072 Outline Perceptual qualities of sound (e.g., timbre, pitch) Sound recording and playback: analog v. digital Sound in VR

3. BPC: Art and Computation – Summer 20073 Curriculum connections Qualities of sound –Music theory Overtone/partial series, temperaments –Physics of musical instruments Modes of vibration

4. BPC: Art and Computation – Summer 20074 Curriculum connections Sound recording and playback –Physics of analog sound reproduction Loudspeaker as electromagnet (demo) –Electronics Amplification / Sound reproduction –Mathematics Digital signal processing: sampling, filtering

5. BPC: Art and Computation – Summer 20075 Curriculum connections Sound in VR –Film / Theatre Sound design

6. BPC: Art and Computation – Summer 20076 Qualities of sound Pitch –Perceptual quality –Closely related to frequency –Doubling of frequency: “octave” –Recorded examples –Demonstration (musical instrument)

7. BPC: Art and Computation – Summer 20077 Qualities of sound Timbre –Tone “color” –Made up of combinations of (related) harmonics or “partials” E.g., modes of vibration of string –Part of how we distinguish different instruments/voices –Recorded examples –Demonstrations (voice, musical instrument

8. BPC: Art and Computation – Summer 20078 Qualities of sound Noise –No clearly identifiable pitch –Combination of unrelated harmonics –Analogy with white light –Examples –Demonstrations (voice, musical instrument)

9. BPC: Art and Computation – Summer 20079 Qualities of sound Time variation –Most naturally occurring sounds are not static; i.e., they vary over time Amplitude Pitch Timbre –Examples –Demonstration

10. BPC: Art and Computation – Summer 200710 Sound recording technologies Analog recording – Changes in air pressure recorded as continuously variable physical quantity Phonautograph: squiggles on carbon- coated drum Phonograph: squiggles on vinyl Tape recorder: change in magnetic field orientation in granules of iron oxide Movie film: changing light/dark pattern on plastic film

11. BPC: Art and Computation – Summer 200711 Analog recording technologies Phonautograph

12. BPC: Art and Computation – Summer 200712 Analog recording technologies Mechanical: Gramophone, LP record, etc.

13. BPC: Art and Computation – Summer 200713 Analog recording technologies Magnetic: Wire, tape recorder.

14. BPC: Art and Computation – Summer 200714 Analog recording technologies Optical: movie soundtrack.

15. BPC: Art and Computation – Summer 200715 Analog sound reproduction Amplification Loudspeaker demo

16. BPC: Art and Computation – Summer 200716 Digital recording Digital: “device or system that represents changing values as discontinuous, or ‘discrete,’ values.” Example: clock with number readout.

17. BPC: Art and Computation – Summer 200717 Digital recording concepts Sampling rate: e.g., 44,100 samples/second (CD rate) Word size: e.g., 16 bits (= 2 bytes) Quantization: selection of sample from finite set of values. Nyquist frequency: 1/2 sampling rate (so = ~22Khz for CD)

18. BPC: Art and Computation – Summer 200718 Possible special topics CD recording technology MP3 compression MIDI: Musical Instrument Digital Interface

19. BPC: Art and Computation – Summer 200719 Sound in VR Sound server concepts –Sounds assigned location in 3D audio space (often corresponding to visible 3D model) –Sound rendering consists of altering sound volume in speaker array to indicate direction and distance –Sound mixing happens automatically –*Internet telephony (i.e., live audio) supported

20. BPC: Art and Computation – Summer 200720 Uses of sound in VR Communication (via telephony) Sound effects Music selections Ambient audio Live audio (via telephony) Previous projects have involved controlling synthesizers or musical instruments remotely.

21. BPC: Art and Computation – Summer 200721 Sources of sound in VR Studio and field recordings Free sounds: http://freesound.iua.upf.edu/ Commercial recordings* *discussion about “fair use”

22. BPC: Art and Computation – Summer 200722 Sound in VR Demonstration –Proximity triggering –(Variable) Distance attenuation –Sound localization

23. BPC: Art and Computation – Summer 200723 Discussion