1. Introduction to Acoustics dr inż. Michał Bujacz bujaczm@p.lodz.pl Visitng hours: tuesday 15:00-16:00 wednesday 10:00-11:00 „Lodex” 207

2. Acoustics [gr. akoustikós ‘related to hearing’] field of physics and engineering that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound http://www.physics.byu.edu/ 2

3. Sound „phys. mechanical disturbance in a compressive medium capable of inducing an auditory sensation, as well as the auditory sensation itself” (Encyklopedia PWN) 3

4. Longitudinal wave (wzdłużna) Particles oscillate in the direction of wave propagation. Areas of increased and decreased pressure. http://www.physics.byu.edu/ What’s the range of movement of the air particles moved by sound ? 0.008nm t o 0.1 mm 4

5. Harmonic signal http://hyperphysics.phy-astr.gsu.edu 5

6. Physics vs. perception Physical definitions: - Intensity (natężenie) or amplitude (amplituda) - Frequency (częstotliwość) - Spectrum (widmo) - Speed (prędkość) Psychoacustic definitions: - Loudness (głośność) - Pitch/tone (wysokość/ton) - Tembre (barwa) 6

7. Speed of sound c = 344 m/s c = 331 + 0,6*T[ o C] SubstanceTemperature (°C)Speed (m/s) Gases Carbon Dioxide0259 Oxygen0316 Helium0965 Liquids Ethanol201162 Mercury201450 Water201482 Solids Copper-5010 Glass-5640 Steel-5960 7

8. Intensity of sound Intensity = the amount of energy passing through an area in time http://hyperphysics.phy-astr.gsu.edu How does amplitude change with distance ? 8

9. Measures of sound level Pressure (rms) from 0.00002 N/m2 (threshold of hearing) to 20 N/m (threshold of pain) atmospheric pressure 100000 N/m2 9

10. Decibel scale Ratio of power: Ratio of amplitude: dBpower ratioamplitude ratio 601 000 0001 000 50100 000316.2 4010 000100 301 00031.62 2010010 3.162 63.98 2 321.414 011 -30.5 0.7071 -60.2510.5 -100.10.3162 -200.010.1 -300.0010.03162 -400.000 10.01 10

11. Confusing „sound levels” Sound Power Level (SWL) - energy emitted by sound source per second (cause) Sound Pressure Level (SPL) - pressure (amplitude) changes at receiver (effect) Sound Intensity Level (SIL) - energy delivered to receiver area per second (effect) 11

12. http://www.physics.byu.edu/ 12

13. Loudness 1Fon = 1dBSPL at 1kHz 13

14. Frequency 14

15. Audio frequency ranges TonesExamples Low bass : 20 – 80 Hz Lowest two octaves. Explosions, storms, lowest church organ notes Upper bass : 80 – 320 Hz 3 th – 4 th o ctaves Drums, bass, cellos, wind instruments Lower mid : 320 – 2560 Hz 5 th – 7 th o ctaves Most instruments and human speech Upper mid : 2560 – 5120 Hz 8 th o ctave Highest notes on most instruments, whistles, most sensitive perception range High/treble : 5120 Hz – 20000 Hz 9 th - 10 th octave Percussion (hi-hat, cymbal), higher harmonics of sounds, noise 15

16. Human perception 16

17. Musical tone (pitch) Musical scales – divided into octaves (intervals), e.g. C (dur) A 4 = 440Hz Psychoacoustic scales – Mel or Bark http://www.sfu.ca/ 17

18. Freq. components 18

19. Fourier transform 19

20. Spectrum of a sound 20

21. Real spectrum Amplituda (dB) Częstotliwość (Hz) 21

22. Cutting the spectrum into octaves 22

23. Tembre/quality Set of features distinguishing sounds of the same base frequency on different instruments Spectrum dependent (harmonics and noise) and transients (sudden changes) Described semantically (np.brightness, warmth, coarsness, clarity) 23

24. Sound envelope 24

25. Anatomy of hearing 25

26. Cochlea 26

27. Future topics - Psychoacoustics - Spatial audio - Room acoustics (wave phenomena) - Spectrum analysis (Fourerier, DFT, FFT) - Noise and sound standards - Math of Music - Electroacoustics - Studio equipment - Sound synthesis - Speech signals - Speaker sets 27

28. Graphical materials PROGRAMMING EXERCISE BOARD EXERCISE ORAL EXERCISE HOMEWORK EXERCISE 28