Psychological psychoacoustics is needed to perceive sound to extract features and meaning from them -human experience

Transcription

1 Physics of Sound qualitative approach basic principles of sound Psychological psychoacoustics is needed to perceive sound to extract features and meaning from them -human experience Fundamentals of Digital Audio any sound can be generated from 1.principles 2.analysis 3.synthesis overview of digital audio synthesis concepts computer music basics sampling, additive/subtractive synthesis, multiple wavetable, granular synthesis, FFT abstractions Mapping Strategies sound design for interaction Interactive Music turning analytical models into new sounds

2 Sources of the course materials Designing Sound by Andy Farnell, Machine Musicianship by Robert Rowe, The Theory and Techniques of Electronic Music by Miller Puckette, The Computer Music Tutorial by Curtis Roads, Handmade Electronic Music: The art of Hardware Hacking by Nicolas Collins Example codes Tom Erbe Andy Farnell Miller Puckette

3 Sound "Sound is an organized movement of molecules caused by a vibrating body in some medium - water, air, rock or whatever. Stevens, S.S. & Warshofsky,Fred.: Sound and Hearing : Time-Life Science Library : 1980 "Sound is the auditory sensation produced through the ear by the alteration... in pressure, particle displacement, or particle velocity which is propagated in an elastic medium. Olsen, Harry F.:Music, Physics and Engineering : Dover Publications, Inc. N.Y., 2nd ed. : Physical phenomenon, vibration of air, a physical disturbance (a "pressure wave") that travels from a source

4 Sound If a tree falls in the forest, and there is no one to hear it, will there be a sound? so, it can refer to your sensation when that wave reaches to your ear-drum.

5 Sound If a tree falls in the forest, and there is no one to hear it, will there be a sound? so, it can refer to your sensation when that wave reaches to your ear-drum. The source, or creation of sound waves, The nature of these wave, and how they are transmitted, The detection mechanism (usually, your ear)

6 Sound If a tree falls in the forest, and there is no one to hear it, will there be a sound? so, it can refer to your sensation when that wave reaches to your ear-drum. The source, or creation of sound waves, The nature of these wave, and how they are transmitted, The detection mechanism (usually, your ear) 1) Production 2) Propagation 3) Perception of sound.

7 Sound 1) Production of sound comes from rapidly vibrating things. Feel your throat as you talk, your vocal cords vibrate. ALL sound comes from some kind of vibrations. a guitar string vibrate when you pull it... you see the vibration that causes the sound

8 Sound 2) Propagation of sound depends on the "medium", the material. Mostly, we'll think of sound in air. We'll talk about HOW sound can travel through air - we speak of the "sound wave", which travels. (In air, at about 344 meters/sec)

9 Sound 3) Perception happens at our ears. There are physical interactions with features inside your ear, which result in electrical signals to your brain, which are interpreted, as "sound". Some aspects of this are very well understood, but the "higher level" (neural/cognitive) aspects are still very much "under study".

10 Sound SOUND arises when something vibrates... Vibration means something going back and forth and some rate, at some frequency. we might say it's periodic, it keeps moving back and forth, passing the starting position at some frequency. we can easily conclude that sound is a wave (of some kind)

11 Physics of sound Waves waves carry energy from one place to another they move by propagation through a medium medium is made to vibrate waves are imaginary things instantaneous velocity of the medium is different than the speed of the wave

12 Physics of sound Propagation sound bounces around the material like a ripples in a pool the effect of this moving wavefront is a wave Sound waves in a gas are longitudinal the movement of material points is forward and backwards in the same direction as the propagation. transverse waves move in a direction perpendicular to the displacement of the medium. like those seen on the surface of the water

13 Physics of sound Longitudinal sound waves Transverse waves light waves Longitudinal First, compression of the medium Then, rarefaction Speaker- ear Transverse

14 Physics of sound periodic motion examples in nature: trees swaying, tides key points - for motion that repeats itself or it is periodic there is a regular time characteristic of that motion there is a force that constantly acts to restore the object to its midpoint or equilibrium point Simple Harmonic Motion- SHM

15 Physics of sound

16 Physics of sound

17 Physics of sound Amplitude The amplitude of an wave is a measured quantity at some point. in all cases it has negative and positive magnitudes relative to the rest point for sound waves, a positive amount corresponds to a compression of the medium and a negative value to the rarefaction. Speed taken as constant within the life of a sound event in the air, it travels at about 344m/s, faster in liquid and even more in a solid Wavelength measure of how long a wave is in meters, and it is measured between the closest 2 points with the same displacement movements in the same direction.

18 Physics of sound Frequency and Period The motion of some point, being displaced, returning through its rest point, overshooting and coming all the way back to its rest point once again, is a cycle. and the time taken to do this is the period in seconds. the number of times this happens each second is the frequency Phase It describes an orientation with respect to an earlier orientation like upside down back and forth

19 Physics of sound wave repeats itself, e.g. mass of a spring distance for the wave to repeat called wavelenght frequency = number of cycles / second = Hz period = time for wave to repeat frequency x wavelength = speed or velocity f x λ =v

20 Physics of sound called "superposition of waves". It's a description of how waves interact, they superpose (add), but are individually unaffected.

21 Physics of sound superposition of sound waves Two sounds of slightly different frequencies can add At some times, they re in synch ( in phase ) => add up (constructive, LOUD) At other times, they get out of synch => cancel (destructive, SOFT) Alternates back and forth, at beat freq = freq(#1) - freq(#2)

22 Physics of sound

23 Sound Design and Interactive Music Diagram of the Ear

24 Sound Design and Interactive Music Diagram of the Ear

25 Diagram of the Ear

26 Diagram of the Ear

27 Diagram of the Ear synapse Ions cause the movement of 'packages' of another chemical, a 'neurotransmitter' called glutamate. The glutamate stimulates the nerve fibre, and causes an electrochemical message to rush along the nerve in the direction of the brain

28 Digital Audio Digital Signal Processing converts naturally occurring analog signals into digital form so those signals can be enhanced and modified for various applications. In +me analog signals have infinite number of values

29 Digital Audio In +me analog signals have infinite number of values Digital Advantage - Processed and transmitted more efficiently and reliably - Reproduced with greater accuracy and clarity - Stored more compactly - Not as affected by unwanted voltage fluctuations (noise) Analog signals Purpose is to remove unwanted Signals Nyquist Sampling theorem Analog to Digital Converter Digital Signal Processing Digital to Analog Converter Reconstruction filter lop hip bp Amplifying modifying To get rid of the junk

30 Digital Audio Nyquist Sampling theorem Hz CD sampling Hz DAT Hz DVD video Hz DVD audio

31 Digital Audio Nyquist Sampling theorem Sample and hold In between samples keep in at that sample

32 Digital Audio Analog to Digital Converter Quantization Signing digital quantity for that analog value

33 Digital Audio

34 Digital Audio Analog to Digital Converter 4 bit 8 bit 16 bit 32 bit 64 bit

35 Digital Audio Digital Signal Processing converts naturally occurring analog signals into digital form so those signals can be enhanced and modified for various applications. In +me analog signals have infinite number of values