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Introduction to Acoustics

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. Acoustics. [gr. akoustikós ‘related to hearing’]

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Introduction to Acoustics

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  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/

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

  4. Longitudinal wave (wzdłużna) • Particles oscillate in the direction of wave propagation. • Areas of increased and decreased pressure. What’s the range of movement of the air particles moved by sound? http://www.physics.byu.edu/ 0.008nm to 0.1mm

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

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

  7. Speed of sound • c = 344 m/s • c = 331 + 0,6*T[oC]

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

  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

  10. Decibel scale • Ratio of power: • Ratio of amplitude:

  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)

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

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

  14. Frequency

  15. Audio frequency ranges

  16. Human perception

  17. Musical tone (pitch) • Musical scales • – divided into octaves (intervals), e.g. C (dur) • A4 = 440Hz • Psychoacoustic scales • – Mel or Bark http://www.sfu.ca/

  18. Freq. components

  19. Fourier transform

  20. Spectrum of a sound

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

  22. Cutting the spectrum into octaves

  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)

  24. Sound envelope

  25. Anatomy of hearing

  26. Cochlea

  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

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