Introduction to Acoustics dr inż. Michał Bujacz Visitng hours: tuesday 15:00-16:00 wednesday 10:00-11:00 „Lodex” 207.

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Presentation transcript:

Introduction to Acoustics dr inż. Michał Bujacz Visitng hours: tuesday 15:00-16:00 wednesday 10:00-11:00 „Lodex” 207

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 2

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

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 ? 0.008nm t o 0.1 mm 4

Harmonic signal 5

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

Speed of sound c = 344 m/s c = ,6*T[ o C] SubstanceTemperature (°C)Speed (m/s) Gases Carbon Dioxide0259 Oxygen0316 Helium0965 Liquids Ethanol Mercury Water Solids Copper-5010 Glass-5640 Steel

Intensity of sound Intensity = the amount of energy passing through an area in time How does amplitude change with distance ? 8

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

Decibel scale Ratio of power: Ratio of amplitude: dBpower ratioamplitude ratio

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

Loudness 1Fon = 1dBSPL at 1kHz 13

Frequency 14

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 – Hz 9 th - 10 th octave Percussion (hi-hat, cymbal), higher harmonics of sounds, noise 15

Human perception 16

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

Freq. components 18

Fourier transform 19

Spectrum of a sound 20

Real spectrum Amplituda (dB) Częstotliwość (Hz) 21

Cutting the spectrum into octaves 22

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

Sound envelope 24

Anatomy of hearing 25

Cochlea 26

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

Graphical materials PROGRAMMING EXERCISE BOARD EXERCISE ORAL EXERCISE HOMEWORK EXERCISE 28