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Topic 3 Physical Acoustics Review

Topic 3 Physical Acoustics Review. WARNING!!!!. This is a REVIEW. Mastery is ESSENTIAL to understand the material later in the course. If you found this material particularly challenging in previous courses it is, spend the time on it NOW. Learning Objectives.

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Topic 3 Physical Acoustics Review

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  1. Topic 3 Physical Acoustics Review SPPA 6010 Advanced Speech Science

  2. WARNING!!!! • This is a REVIEW. • Mastery is ESSENTIAL to understand the material later in the course. • If you found this material particularly challenging in previous courses it is, spend the time on it NOW. SPPA 6010 Advanced Speech Science

  3. Learning Objectives • Outline the physical processes underlying simple harmonic motion using the mass-spring model • Describe the molecular basis of sound wave propagation SPPA 6010 Advanced Speech Science

  4. Mass (inertia) Elasticity Friction Spring Mass Model SPPA 6010 Advanced Speech Science

  5. What is sound? • It may be defined as the propagation of a pressure wave in space and time. • propagates through a medium SPPA 6010 Advanced Speech Science

  6. Medium is composed of molecules Molecules have “wiggle room” Molecules exhibit random motion Molecules can exert pressure A B Sound-conducting media SPPA 6010 Advanced Speech Science

  7. Model of air molecule vibration (Time 1) Air molecules sitting side by side Rest positions SPPA 6010 Advanced Speech Science

  8. Model of air molecule vibration (Time 2) SPPA 6010 Advanced Speech Science

  9. Model of air molecule vibration (Time 3) SPPA 6010 Advanced Speech Science

  10. Model of air molecule vibration (Time 4) SPPA 6010 Advanced Speech Science

  11. Model of air molecule vibration (Time 5) SPPA 6010 Advanced Speech Science

  12. a b c d Time 1 2 3 4 5 Distance Model of air molecule vibration SPPA 6010 Advanced Speech Science

  13. Time 1 2 3 4 5 Distance Wave action of molecular motion SPPA 6010 Advanced Speech Science

  14. Amplitude waveform Position Time SPPA 6010 Advanced Speech Science

  15. Amplitude waveform Question: How long will this last? Amplitude Time SPPA 6010 Advanced Speech Science

  16. Model of air molecule vibration Time 1 2 3 4 5 Questions: Where is a region of compression? Where is a region of rarefaction? Pressure measuring device SPPA 6010 Advanced Speech Science

  17. For example… Pressure Time SPPA 6010 Advanced Speech Science

  18. Learning Objectives • Define the key characteristics of sinusoidal motion (amplitude, frequency/period and phase) • Outline the relationship between the frequency and wavelength of a sound wave SPPA 6010 Advanced Speech Science

  19. Pressure vs. time (pressure waveform) Amplitude Phase (deg) Phase: when a period begins Frequency (F): rate that waveform repeats itself (1/T) Pressure Period (T) Time SPPA 6010 Advanced Speech Science

  20. Phase SPPA 6010 Advanced Speech Science

  21. Initiating a sound waves that differ only in phase A force is applied to molecule at frequency fand time t same force applied at frequency f at time t+a where a < the period of vibration SPPA 6010 Advanced Speech Science

  22. Features of a pressure waveform • Amplitude • Measured in pressure units • peak amplitude • peak-to-peak amplitude • Instantaneous amplitude • Period and Frequency • Period measured in time (basic quantity) • Frequency is a rate measure (per unit time) expressed as Hertz (s-1) • May be expressed as octaves, semitones, etc • Phase • Measured in degrees (relative to period length) • 0-360 degrees SPPA 6010 Advanced Speech Science

  23. Spatial variation in pressure wave wavelength () is the distance covering adjacent high and low pressure regions SPPA 6010 Advanced Speech Science

  24. For example… Wavelength () Pressure Distance SPPA 6010 Advanced Speech Science

  25. Relation between frequency and wavelength =c/F where : wavelength F: is the frequency c: is sound speed in medium (35,000 cm/sec) SPPA 6010 Advanced Speech Science

  26. Additional Concepts • Propagation of waves • Transmission • Absorption • Reflection • Reverberation SPPA 6010 Advanced Speech Science

  27. Learning Objectives • Draw and describe time-domain and frequency-domain representation of sound • Distinguish between simple and complex sound sounds with regard to physical characteristics and graphical representations • Distinguish between periodic and aperiodic sounds with specific emphasis on terms such as fundamental frequency/period, harmonics, and overtones • Distinguish between continuous and transient sounds • Describe how waves sum, define Fourier's theorem and be able to describe the basics of Fourier analysis SPPA 6010 Advanced Speech Science

  28. Time domain Called a waveform Amplitude plotted as a function of time Frequency domain Called a spectrum Amplitude spectrum amplitude vs. frequency Phase spectrum phase vs. frequency May be measured using a variety of “window” sizes Graphic representation of sound SPPA 6010 Advanced Speech Science

  29. Same sound, different graphs Time domain Frequency domain SPPA 6010 Advanced Speech Science From Hillenbrand

  30. Classification of sounds • Number of frequency components • Simple • Complex • Relationship of frequency components • Periodic • Aperiodic • Duration • Continuous • Transient SPPA 6010 Advanced Speech Science

  31. Simple periodic sound • Simple: one frequency component • Periodic: repeating pattern • Completely characterized by • amplitude • period (frequency) • phase • Other names: sinusoid, simple harmonic motion, pure tone SPPA 6010 Advanced Speech Science

  32. Simple periodic sound: Graphic appearance SPPA 6010 Advanced Speech Science From Hillenbrand

  33. Complex periodic sounds • Complex: > one frequency component • Periodic: repeating pattern • Continuous • Frequencies components have a special relation • Lowest frequency: fundamental frequency • Symbol: fo • Frequency component with longest period • Higher frequency components: harmonics • integer (whole number) multiples of the fo SPPA 6010 Advanced Speech Science

  34. Complex periodic sounds: Graphic appearance • Time domain: • repeating pattern of pressure change • within the cycle, things look complex • Frequency domain: • spectral peaks at evenly spaced frequency intervals • “picket fence” appearance • Auditory impression: sounds ‘musical’ SPPA 6010 Advanced Speech Science

  35. Complex periodic sounds: Graphic appearance SPPA 6010 Advanced Speech Science From Hillenbrand

  36. SPPA 6010 Advanced Speech Science

  37. Amplitude vs. Phase Spectrum Amplitude spectrum: different Phase spectrum: same SPPA 6010 Advanced Speech Science

  38. Amplitude vs. Phase Spectrum Amplitude spectrum: same Phase spectrum: different SPPA 6010 Advanced Speech Science

  39. (Complex) Aperiodic sounds • Complex: > one frequency component • Aperiodic: Does not repeat itself • Frequency components are not systematically related • May be • Continuous • Transient SPPA 6010 Advanced Speech Science

  40. Aperiodic sounds: Graphic appearance • Time domain: • no repeating pattern of pressure change • Frequency domain: • the spectrum is dense • No “picket fence” • Auditory impression: sounds ‘noisy’ SPPA 6010 Advanced Speech Science

  41. Aperiodic sounds: Graphic appearance SPPA 6010 Advanced Speech Science From Hillenbrand

  42. Analysis of complex waves • Waves can be summed • Complex waves are the sum of simple waves • Fourier: French Mathematician: • Any complex waveform may be formed by summing sinusoids of various frequency, amplitude and phase • Fourier Analysis • Provides a unique (only one) solution for a given sound signal • Is reflected in the amplitude and phase spectrum of the signal • Reveals the building blocks of complex waves, which are sinusoids SPPA 6010 Advanced Speech Science

  43. Learning Objectives • Draw and differentiate the waveform and the waveform envelope • Draw and differentiate the amplitude spectrum, the phase spectrum and the spectrum envelope SPPA 6010 Advanced Speech Science

  44. The “envelope” of a sound wave • Waveform envelope: • imaginary smooth line that follows the peak of the amplitude of a sound pressure waveform • Spectrum envelope: • Imaginary smooth line drawn on top of the amplitude spectrum SPPA 6010 Advanced Speech Science

  45. Waveform envelope Time SPPA 6010 Advanced Speech Science

  46. Spectrum envelope SPPA 6010 Advanced Speech Science From Hillenbrand

  47. Thought Question Can an aperiodic and complex periodic sound have identical spectrum envelopes? SPPA 6010 Advanced Speech Science

  48. Amplitude Spectrum: Window Size • “short-term” vs. “long-term average” amplitude spectrum SPPA 6010 Advanced Speech Science

  49. “Instantaneous” Amplitude Spectra SPPA 6010 Advanced Speech Science

  50. (Long Term) Average Amplitude Spectrum SPPA 6010 Advanced Speech Science

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