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Basic Acoustics: Simple and Complex Waves

Basic Acoustics: Simple and Complex Waves. THE SPEECH PROCESS . SPEAKER LISTENER ACOUSTICS NEURO- PRODUCTION AUDITION MUSCULAR AERODYNAMICS ARTICULATION NEUR0- PERCEPTION RECEPTION.

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Basic Acoustics: Simple and Complex Waves

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  1. Basic Acoustics:Simple and Complex Waves

  2. THE SPEECH PROCESS SPEAKER LISTENERACOUSTICSNEURO- PRODUCTION AUDITIONMUSCULAR AERODYNAMICS ARTICULATION NEUR0- PERCEPTION RECEPTION

  3. There is a one-to-many relation between the articulatory gesture (e.g., lip closure) and the acoustic consequences of that gesture in different contexts. Yet the listener is able to deal with these variable signals and can usually get back to the intended gesture. ARTICULATORY GESTURE/p/ /k/pa pu pi / ka ku kiACOUSTIC CONSEQUENCES /p/ /k/PERCEPT

  4. We will explore here both of these phases of the speech process. We begin today with the acoustic phase: transmission of sound by movement of air molecules—i.e., by sound waves. We are centrally concerned with the complex sounds produced by the human vocal tract, but we will begin with a simpler description of vibration and wave motion.... and then will work our way into the vocal tract.

  5. A TYPE OF SIMPLE VIBRATORY MOVEMENT:TUNING FORKS Rest Force (inward displacement) Elasticity (rest position) Inertia (outward displacement) Elasticity (rest position) Etc.The motion of the prongs sets adjacent AIR MOLECULES into a similar pattern of movement about their rest position.

  6. Representing wave motion:.01 sec 300 Hz Wave A: .01 sec Wave B: 300 Hz 600 Hz Wave C: .01 sec

  7. SOME PROPERTIES OF WAVES amplitude (dB): maximum displacementfrequency: number of cycles per second (Hz)period: number of seconds per cyclevelocity: speed in a certain directionwavelength ():distance in space occupied by one cycle; = velocity / frequencyphase: time aspect of wave; that part of cycle through which wave has advanced at a given point in time

  8. Physical dimensions of waves: amplitude wavelength = velocity / frequencyTemporal dimensions of waves: period frequency = 1 / period velocity (of sound in air = 340 meters/sec)If a wave's period = 20 ms, what is its frequency?If a wave's frequency = 100 Hz, what is the wavelength?What is the frequency of a sound with a wavelength of 68 cm?

  9. 2 waves 180° out of phase PHASE: Waves A and B have the same frequency & amplitude,but different phases: 90° Wave A 0° Time  Wave B

  10. To define a sine wave, need to know: frequency amplitude phase

  11. Vibration of Air Molecules Let’s return to our tuning fork ...The motion of the prongs sets surrounding air molecules into a similar pattern of movement about their rest position. In addition, the movement of air particles closest to the tuning fork exerts force on adjacent particles. Thus the disturbance is transmitted outward from source via a pressure wave.

  12. A A B A C B A B C A B C A B C A B C A B C A B C A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F G A B C D E F GEach particle: movement over time transcribes wave motionBody of air: areas of compression and rarefaction TIME

  13. WAVEFORMS: represent air particle displacement OR air pressure variation PARTICLE MOTIONAIR PRESSURE VARIATION Amount of Displacement Rest position Time + Pressure - Equilibrium Time

  14. Sound waves produced by the human vocal tract are complex:Complex aperiodic ( = non-repeating) Complex periodic ( = repeating) COMPLEX WAVES

  15. Complex waves: can be represented as the sum of a number of sine wavesComponent (wave) = one of a # of sine waves present in a complex waveFourier analysis: analysis of complex wave into its sine wave componentsDescription of complex waves: frequency amplitude phase of component waves

  16. Two important relations between a complex wave and its components:(1) Amplitudes add Sum of displacement of components at a given point in time = displacement of complex wave at that point in time(2) Frequency of lowest-frequency component wave = frequency of complex wave (in naturally occurring periodic sounds)

  17. Representing components of complex waves:POWER SPECTRUM100 200 300 Frequency (Hz) Amplitude PHASE is not represented: The phase at which components combine affects wave shape, but it does not affect how the complex wave sounds to the human ear. With one exception ...

  18. FUNDAMENTAL FREQUENCY Fundamental frequency (F0) of complex periodic wave: = frequency of repetition of complex wave = highest common factor of component frequencies = lowest-frequency component in natural soundsIn naturally occurring periodic sounds: all components are at whole # multiples of F0 These multiples are HARMONICS.(PRAAT demonstration: combining sine waves to form complex wave)

  19. No vibration A first foray into acoustic analysis: VOICE ONSET TIME VOT = interval between release of articulatory stricture and onset of voicing Release of stricture Supralaryngeal gesture Articulators together Articulators apart Articulators apart Glottis No vibration Glottis Glottis TIME 

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