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Speech Science - CSD 250 CSD 250 Speech Science Basic...

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Unformatted text preview: CSD 250 CSD 250 Speech Science Basic acoustics 1 Next in the speech chain Next in the speech chain Acoustics? Why? Acoustics? Why? The science and technology of the production, transmission, reception, and effects of sound and vibration Acoustics provides objective, quantifiable measures of speech Describing sound: Wave Describing sound: Wave Waveform display of speech More on waves More on waves Even if some anxiety occurs, as it is bound to in life, you should always be calm. Like a wave, which rises from the water and dissolves back into the water, these disturbances are very short, so they should not affect your basic mental attitude. From “The Heart of the Buddha’s Path” by the Dalai Lama (1995) Generating waves Generating waves Source Medium – Examples: stone thrown to a river, tuning fork, falling book hitting the ground, piano or violin strings – For speech: vocal fold vibration, turbulent airflow, sudden release of closure – Examples: water/air particles – For speech: air particles Wave propagation Wave propagation Movement of sound source results in movement of air particles, causing fluctuations in air pressure Fluctuations in air pressure include – Compression, where pressure is high – Rarefaction, where pressure is low What does that mean? What does that mean? Demo 1 Demo 2 Wave vs. particles Wave vs. particles It is the wave that propagates The medium (air or water particles) does not propagate Plotting air pressure Plotting air pressure fluctuation Plotting water pressure Plotting water pressure fluctuation Describing sinusoidal Describing sinusoidal waves Amplitude (Perceptually: Loudness) Frequency/Period (Perceptually: Pitch) Phase Propagation Velocity Wavelength Amplitude Amplitude The maximum deviation from the zero line in air pressure: a’­a & b’­b Frequency Frequency The number of times that a periodic event repeats itself for some standard interval of time Frequency & period Frequency & period Frequency (f ): How often an event repeats itself or completes a cycle within an amount of time (in cps or Hz) Period (T ): The duration of a cycle (in sec or ms) 1 f= T Amplitude and frequency Amplitude and frequency are independent of each other Fig. 2.1: Same freq, diff amp Fig. 2.3: Same amp, diff freq Phase Phase The timing of wave propagation Propagation Velocity & Propagation Velocity & Wavelength Propagation Velocity – The speed of wave – Unit: cm/sec, ft/sec Wavelength – The distance (not time) between recurring events – Unit: cm, ft Wavelength ≠ period Wavelength Wavelength is a measure of distance Period is a measure of time Velocity, frequency, Velocity, frequency, wavelength c = fλ c : Velocity (cm/sec) λ : Wavelength (cm) f : Frequency (Hz) Since f = 1 / T, therefore c = λ / T Velocity of sound is about 34,000 cm/sec Acoustics vs. perception Acoustics vs. Frequency: Acoustic measure of periodicity Pitch: Perceptual response to frequency Amplitude: Acoustic measure of air pressure Loudness: Perceptual response to amplitude Basic acoustics: Summary Basic acoustics: Summary Amplitude: Sound pressure (cf. Loudness) Frequency: Periodicity (cf. Pitch) Phase Propagation Velocity Wavelength Summary Summary Frequency & Period 1 f= T Sound Velocity, Frequency, & Wavelength c = fλ ...
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