Speech Science Oct 7, 2009
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Speech ScienceOct 7, 2009
Outline
Acoustics
Pure Tone
Simple harmonic motion
Particle movement in Sound
Pressure wave movement in Sound
Interference patterns
Complex tones
Frequency and Pitch
Intensity and Loudness
Wavelength
Resonance
Acoustics
What is acoustics
Study of sound
Speech is a continuously changing stream of sound
Clear understanding of nature of sound is necessary to understand the process of speech production and perception.
Acoustics
Sound
An audible disturbance in a medium caused by a vibrating source Has no physical
substance Invisible Most sounds are
complex
A visible pattern of sound waves. A Basic Guide to the Science of Acoustics by David C. Knight, Franklin Watts, Inc. New York (1960). p. 80.
Pure Tone
Pure tone
Simplest of all sound waves
Consists of only one frequency
Pure tones result from a vibration that repeats itself in exactly the same way (periodic) at a constant number of cycles per second (frequency).
Pure tone has a single frequency
A tuning fork produces a pure tone
http://www.youtube.com/watch?v=C5LS6scAL3E
Pure Tone
Tuning fork vibrates in simple harmonic motion (SMH)
Elasticity
The restoring force that causes a deformed structure to resume its original shape
Inertia The tendency for motion to
continue
Inertia and velocity occur simultaneously.
Pure Tone
Swing analogy: velocity gradation in SMH
Pure Tone
Velocity: The speed of an object.
Frequency: Number of completed
cycles per second (expressed as Hertz)
Period: The time taken for one
complete cycle of movement.
Dampening: Decrease in the
amplitude of displacement over time.
Quiz:
If the frequency were 20 Hz, then what is the period?
Relationship between frequency and period
f (in Hz) = 1/T T (in seconds) = 1/f
Pure Tone
Quiz
Which graph shows how the kinetic energy of an oscillating object varies with time in simple harmonic motion? The period of oscillation is T.
Pure Tone
Particle movement in sound: In pure tone, individual
air particles move in SHM in response to the movement of the pure tone vibrator in SHM.
When 540 Hz tuning fork is sounded, every air molecule in the room soon moves in place.
Each air particle completes 540 cycles per second.
Pure Tone
Movements of vibrating body could be displayed as an amplitude-by-time graph
It is known as waveform
Pure Tone
Both waves have same amplitude but differ in frequency.
Upper one is a low frequency wave, reduced number of cycles per second
Lower one is a high frequency wave, increased number of cycles per second.
Lower one has short period compared to upper one.
Pure Tone
Waveforms of different amplitudes
Pure Tone
Quiz
Among top two waves, which one has higher amplitude?
Among lower two waves, which one has lower frequency?
Pure Tone
Pressure wave movement in sound
The molecules of air vibrating in SHM disturb adjacent molecules, and therefore the disturbance is transmitted away from the source.
The disturbance takes the form of a pressure wave radiating outwards.
Pure tones are periodic, the pressure wave is repeated, followed by evenly spaced pressure waves.
http://www.youtube.com/watch?v=C5LS6scAL3E
Pure Tone
Pressure wave movement in sound
Movement of air particle is in the same direction as wave movement, this type of wave is called longitudinal wave. Sound waves are longitudinal.
Pure Tone
Pressure wave movement in sound
Transverse waves: particles move perpendicular to the direction of the wave
E.g., dipping a finger into water
Pure Tone
Pressure wave movement in sound
Energy released by the source of waves results in compression (area of higher pressure) and rarefaction (area of lower pressure) of solids, liquids or gases.
The alternating areas of compression and rarefaction constitute a pressure wave that moves away from tuning fork in all directions. This can be represented as sine wave.
Pure Tone
Pressure wave movement in sound
A waveform display how amplitude varies with time.
It can represent both particle motion as well as the pressure variation in the medium.
Waveform is a abstract representation of the particle’s displacement from rest during a certain time or variations in air pressure generated by the vibrating source and the air molecules.
Sound
Essential constituents of sound
Three prerequisites A source of energy A vibrating source A medium of transmission
Sound
Interference patterns Particles in air can be responsive to many
signals at once.
Signals of the same frequency can interfere with one another when signals are reflected from a barrier.
Sound
When two signals have a common frequency, then the resulting summed waveform depends on the phrase relationship between the signals
Every cycle has 3600, so that half of a cycle would be 1800, one fourth of a cycle would be 900, and three fourths, 2700.
Sound
The sound interference is acute in concert halls.
If the halls are designed poorly, then it may reverberates excessively
This will cause sound to persist for long period of time
Complex Tones
A tone having more than a single frequency component.
Complex periodic sound waves are those in which the pattern of vibration repeats itself exactly over time.
Complex aperiodic sound wave is one in which the vibration is random and displays no repeatable pattern.
Harmonics Periodic complex vibrations
produce signals in which the component frequencies are integral multiples of the lowest frequency of pattern repetition, or fundamental frequency.
The frequency of each harmonic is whole number multiple of the f0 or first harmonic.
E.g., fo/ first harmonic = 100 Hz; Second = 200 Hz Third = 300 Hz Fourth = 400 Hz Fifth = 500 Hz
http://www.zainea.com/perc1.gif
http://www.sfu.ca/sonic-studio/handbook/Graphics/Law_of_Superposition.gif
Spectrum Amplitude of each
harmonic can be displayed using a amplitude spectrum
Spectrum displays each harmonic as a function of amplitude and frequency.
Aperiodic complex tone
Complex aperiodic tones consists of more than one frequency, but the frequencies are not harmonically related
Summary
Periodic Aperiodic
Simple One component frequency- A pure tone
Complex Two or more component frequencies that are harmonically related: a fundamental frequency plus harmonics-A complex tone
Two or more component frequencies not harmonically related: no fundamental frequency; no harmonicsNoise
Complex Periodic Tones
Sine waves
Square waves
Triangle waves
Sawtooth waves
Quiz
Periodic or aperiodic?
Quiz
Periodic or aperiodic? Periodic or aperiodic?
Fourier Analysis
Complex waves composed of sinusoid waves of frequency, amplitude, and temporal relations.
Fourier analysis allows us to analyze sounds as a number of harmonics.
Based on the discovery that any periodic waveform could be represented as a summation of sinusoidal vibrations.
Frequency and Pitch
Frequency and Pitch
Frequency is the physical attribute of a vibrating source. Measured in Hertz (Hz) or cycles per second
(cps). Example: Vocal folds vibrate between 80 and
500 Hz.
Pitch is a sensation or psychological event.
As frequency increases so does pitch, but not in a linear or one-to-one manner.
Frequency and Pitch The units for pitch are
mels.
How do listeners judge the pitch of complex tones?
For complex periodic tones, listeners judge the pitch corresponding to the fundamental frequency of the harmonic series.
Intensity and Loudness
Loudness and Intensity
Decibel: Relative intensity of two sounds. Unit of measure Logarithmic scale
Loudness and Intensity
Intensity or sound pressure: Physical property of the acoustic signal that
correspond to the amplitude of vibration. Measured using sound level meter in decibels
(dB) which is a logarithmic system.
Loudness: Psychological sensation; perceptual. Increases with intensity, but not a linear or one-
to-one relationship. A phon is a unit of equal loudness.
Intensity and Loudness
Equal loudness levels at different frequencies
Heavy line at the bottom is the absolute threshold of audibility
The lighter lines are the phon curves of equal loudness (tones of 1 k Hz)
For quiet sounds, the amount of intensity needed to cause the perception of equal loudness is large between extreme and middle frequencies.
Wavelength
Wavelength is the distance from any point in one cycle to the corresponding point in the next cycle.
It’s represented by the Greek letter lambda (λ).
It depends on two factors:
λ = c/f Frequency Velocity of sound wave
propagation in the medium
Wavelength
The higher the frequency the shorter the wavelength.
λ = c/f c = velocity of the
sound (344 meters per seond)
f = frequency
High frequency sounds are more directional than low frequency sounds.
Resonance
Resonance
Resonance: Vibratory response to an applied force. Everything that vibrates has a natural or resonant
frequency Swing analogy
Natural resonant frequency: It is a frequency at which a system oscillates with
greatest amplitude when driven by a vibrating source.
Resonant frequency of a vibrating source depends on its physical characteristics
Resonance
The human vocal tract is a tube open at one end.
Can calculate the natural resonant frequency using the formula: f = c/λ; where f = frequency, c = the constant
34,400 cm, and λ = wavelength.
The other resonant frequencies will be odd multiples of the natural resonant frequency.
Conclusion
Pure tone is the simplest sound and has only one frequency and it is periodic.
In pure tone, movement of vibrating body is in simple harmonic motion.
Particle movement and pressure wave movement in sound.
Sound interferences
Related Documents
