Acoustics Exam: Sound in Space & Time

Sound in Space and Time a. How does sound propagate across space and time? i. Sound as a pressure wave 1. Involves molecules bumping into each other 2. Atmospheric pressure: PATM a. How close molecules are together at rest b. Positive vs negati...

Sound in Space and Time a. How does sound propagate across space and time? i. Sound as a pressure wave 1. Involves molecules bumping into each other 2. Atmospheric pressure: PATM a. How close molecules are together at rest b. Positive vs negative i. Positive: closer together (dark bands on spectrogram) 1. Aka. Compression ii. Negative: far apart (lighter bands on spectrogram) 2. Aka. Rarefaction ii. Sound must travel through something (a medium) 3. Solid, liquid, gas 4. A solid is more elastic than a liquid, and a liquid is more elastic than a gas. iii. How does an air molecule move when a sound source causes it to move? 5. Production: Vibration c. Air vibrating back and forth: propagation 6. Rest position 7. Properties of the molecules d. Move back and forth e. Transfer of energy f. friction 8. Mass and elasticity generate inertia and recoil forces, respectively g. Mass iii. Given proper amount of energy, a mass can be set into vibration iv. Inertia: something in motion/ at rest will remain unless acted upon h. Elasticity: ability to stretch but go back to original state (aka. Recoil) Descriptions of Sound b. Physical descriptions of sound: their meanings, how to measure them, and how each relates to one another (when applicable) iv. Temporal: occurs over a period of time 9. Period: amount of time required for the completion of one cycle i. Period = seconds per cycle (seconds/cycle) j. **T=1/f** 10. Frequency: Pitch; Perceptual measure; correlate of frequency (Hz) k. number of cycles per second (cps) l. has an inverse relationship with period m. **f=1/T** 11. Amplitude: Loudness; Perceptual measure; correlate of intensity (dB) n. Logarithmic scale: intensity ratios v. 0dB- auditory threshold (1 IR) vi. 30dB- whisper (100 IR) vii. 50dB- quiet conversation (100,000 IR) viii. 70dB- normal conversation (10 mil) ix. Hearing range: 0-120/140 dB 3. After 85dB hearing damage 4. 140 dB: jet engine v. Spatial: occurs across space 12. Wavelength: distance between compression/rarefaction (high and low pressure) o. This maximum pressure to minimum, and back to maximum is also called a cycle p. Speed of sound: distance covered by wave at room temperature x. c=33,600 cm/s xi. allows ability to localize where sound is coming from q. **λ=c/f** c. Perceptual/psychological descriptions of sound: cannot be described as numbers vi. Pitch vii. Loudness Visual Depictions of Sound d. Know the axes viii. Temporal domain 13. Waveform: amplitude over a period of time 14. Spectrogram: tells us about a moment in time/avg. of energy r. Closer together waves= lower value of fundamental freq. ix. Frequency domain 15. Spectrum: frequency over a period of time s. Includes z-axis: amplitude Types of vibration e. Simple vs. complex vibration x. Simple vibration: Can be described by frequency, amplitude, and starting phase 16. **Pure tones:** A sine wave characterized by frequency, wavelength, or amplitude. t. Graphic way to represent sound waves u. Each cycle of compression and rarefaction, as a function of time A graph with a blue line Description automatically generated 17. Complex vibration: Combinations of simple vibrations f. Periodic vs. aperiodic vibration (with examples) xi. Periodic: repetition of a wave xii. Aperiodic g. What are harmonics and when do they form? xiii. Fundamental frequency: lowest frequency component xiv. Higher wave components -- harmonics 18. Only exist in complex periodic wave forms V. What is resonance? xv. Frequency depends on shape and size of bowl xvi. Adding acoustic energy at just the right time so that it builds upon itself (amplifies) 19. Object + energy=vibration xvii. Resonators: shape acoustic energy (ex. VFs; Helmholtz resonator) h. When do standing waves form? xviii. Standing wave: cause predictable regions of high and low pressure xix. Complex acoustic event: \>1 frequency + periodic acoustic event = harmonics xx. Resonators allow for standing wave development i. Formants: building blocks of vowels xxi. Caused by standing waves xxii. Tube resonators allow multiple frequencies to resonant multiple formants together complex sound waves (vowels) j. Relationship between wavelength and resonance (tube resonators) xxiii. Wavelength just right for tube resonator standing wave k. Pressure conditions associated with tube resonators xxiv. Open tube 20. Open (pressure) at both ends 21. Standing waves form when whole number multiples of one half of a waves' length = length of the tube 22. Half wavelength rule: lowest frequency (fundamental frequency) that will resonate has a wavelength that is twice the length of the tube 23. Patm at ends of the tube=Patm of wave xxv. Tube open at one end and closed at the other 24. Pressure conditions: v. Max pressure at closed end w. Patm (neutral) pressre at open end 25. Standing waves form when odd number multiples of one quarter of a wave fit conditions of tube 26. Quarter wavelength rule: lowest resonant frequency (fundamental frequency) = 4 times the length of the tube  l. Which resonator is most like the human vocal tract? xxvi. Open at one end and closed at the other VI. Damping: energy loss m. Due to friction, absorption, radiation, gravity Critical Damping - A2 Level Physics - YouTube n. Measured through bandwidth: number represents loss VII. Vowel production o. Vocal Fold Vibration xxvii. Myoelastic-aerodynamic theory of phonation 27. Subglottal pressure build up and VFs open 28. Muscle elasticity pull them back together rapidly xxviii. Nature of vocal fold vibration 29. Periodic (technically 'quasiperiodic') 30. Slowly opens 31. Rapidly shuts xxix. Specific manner of vibration generates many harmonics 32. Quarter wavelength rule x. Formant production p. Theories and Models Related to Vowel Production xxx. Source-filter theory (i.e., Acoustic Theory of Vowel Production) 33. Vocal fold vibration = source 34. Harmonics present in source 35. Vocal tract (resonator)= filter of the source 36. Output signal: peaks created due to hitting fundamental frequency filter shape (able to amplify) xxxi. Perturbation Theory: a method for studying how small changes to the vocal tract affect formant frequencies 37. Formants of a perturbed tube will be different from those of a neutral tube 38. Effect of constriction on formants y. Constriction in a region of maximal pressure: formant increase z. Constriction in a region of minimal pressure: formant decrease 39. F1: almost min pressure 40. F2: max pressure 41. F3: almost max pressure xxxii. Stevens and House Model 42. F1 and F2's relationship with tongue position (inverse) a. F1: tongue height b. F2: tongue advancement 43. Impact of lip rounding on all formants, but F2 most affected c. Lip rounding = lower F2 q. Vowel Formants and Vocal Tract Length xxxiii. Formants of a neutral tube 44. Be able to calculate vocal tract length given formant frequencies or a given formant's wavelength 45. Be able to calculate formant frequencies given vocal tract length xxxiv. Impact of age and biological sex on vocal tract length 46. Males F0(rate of VF vibration) drops after age 12 d. Length, tension, thickness, and pathologies affect the rate of vibration e. Subglottal pressure: intensity of VF vibration 47. VT gets longer with maturation in males xxxv. How does vocal tract length affect formant frequencies? 48. Longer= lower resonant freq. 49. Shorter= higher resonant freq. xxxvi. Vowel Identification in Waveforms and Spectrograms 50. Know what to look for f. Formants g. Vertical striations (looks like a barcode/UPC label) h. Somewhat consistent spacing between peaks in the waveform  Spectrogram: Definition & Examples \| StudySmarter