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THE GENERATION OF SOUND

Periodic and aperiodic sounds No sound can be produced without a supply of force or energy. It is the breathing

mechanism that constitutes the energy supply, the expiratory phase. In order that

sound will be generated, the steady flow of energy in one direction has to be

converted into oscillations. For speech, the larynx performs this function, with the

vocal cords. The alternate opening and closing of the vocal cords results in theemission of successive puffs of air into the space above the larynx and this stream of

pulses constitutes the basis of the sound generated by the larynx.

Sound waves are air pressure

waves. At a given instant of time a

sinusoidal air pressure wave will be

distributed in space. It will have a

peak pressure at one point, zero

pressure at a distance of one-

quarter wavelength from the

maximum, a peak pressure at one

wavelength from the first peak, etc.A wave can be described as a

disturbance that travels

through a medium transporting

energy from one location to

another location.

Sound-> longitudinal wave and

a mechanical wave.

Longitudinal wave is a wave

which particles of medium

move in a direction parallels tothe direction in which the wave

moves. Mechanical wave requires a medium in order to transport their energy.

Theyre not capable of transmitting invacuum (vaco). Wave length is the length of one

complete circle of a wave.

Compression (region of high air pressure)/Rarefaction (region of low air pressure)

A wave is an energy transport and the amount of energy carried by a wave is related to

the amplitude a measure of force. A high energy wave is characterized by a high

amplitude and a low energy wave by a low amplitude. Amplitude is an amount of

maximum displacement of a particle on the medium from its rest position.

The greater of the ampl

Intensity: The amount of energy which is transported past a given area of the mediumper unit of time is known as the intensity of the sound wave. The greater the

amplitude of vibrations of the particles of the medium, the greater the rate at which

energy is transported through it, and the more intense that the sound wave is.

Loudness is subjective depending on the person/intensity is objective.

Frequency of vibrations refers to how often the particles of the medium vibrate when

a wave passes through the medium, the unit of frequency is Herz (Hz) or cycle per

second.

Intensity -> decibels (dB)

Frequency-> rate of vibration of the vocal folds.

Increasing length and mass (ex. Double-bass/violin): Increasing tension -> higher

frequency and vibration

Each standing wave pattern is referred to as a mode of vibration, so the string is

vibrating simultaneously in a number of different modes, that is over its whole length.

Imagine Fundamental Frequency (Fo)= 100 Hz which

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This mode of vibration involving the whole length of the string is called the

fundamental mode and the frequency to which it gives rise is the fundamental

frequency. The frequency produced by other modes (B, C, D) are harmonics. The

prequency of harmonics are multiples of the fundamental frequency.

The period of a wave is the time for a particle on a medium to make one complete

vibrational cycle. Frequency and period are different, yet related quantities. Frequency

is the cycles per second and period second per a cycle.P=L/f second/cycle F=L/P

Amplitude is a measure of force. It is linked with the sensation of loudness, and it

refers to the maximum displacement in a cycle of movement.

The time taken by one cycle of opening and closing of the cords depends upon the

balance between the subglottal

pressure and the resistance offered by

the vocal folds. The physical factors

which regulate the frequency of

vibration are the mass, length and

tension of the vibrating structures. The

vocal folds have many modes of

vibration in addition to the

fundamental mode. Frequencies

generated by these other modes of

vibration are multiples of this

fundamental frequency.

The glottal wave is periodic, that is it consists of repeated cycles of motion, and

therefore it must be made up of a fundamental frequency plus a range of harmonics.

The fundamental frequency has the greatest amplitude, and the amplitude of each

succeeding harmonic would be falling off progresively as the frequency increases.

In speech the fundamental frequency is

changing all the time but the components of

the larynx tone are always harmonics of the

fundamental and the effect of the

resonances of the vocal tract is to produce a

peak in the spectrum of the output at the

harmonics which are the closest to the true

resonance

The spectrum of the resulting sound always

has the same general outline or envelope

although the fundamental frequency is

continually changing. This means a

certain sameness of quality is heard in a

range of sounds with different

fundamentals. If this were not the case,

speech sounds could not fulfill the

linguistic function that they in fact have.

The term used for a resonance of the

system in this context is a formant.

Differences in formant structure are the

result of differences in articulationwhich affect the shape and hence the

dimensions of the vocal tract. The most

important modifications are due to

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different places in the tract, the location corresponding to what is referred to

phonetically as the point of articulation of the sound.

What about voiced consonants such as /z/?

CORRELATOS ARTICULATORIOS, ACSTICOS Y AUDITIVOS

The spoken message undergoes a series of modifications during speechcommunication.

It is convenient for us to grasp the dynamic nature of speech and the non-monotonic

relations between articulatory, acoustic and auditory parameters of speech analysis.

The speech chain:Transmission Phase

- String of language units

- Chain of nerve impulses

- Sequence of muscle movements

- Train of sound waves

Reception Phase

-Train of sound waves

-Sequence of muscle movements

-Chain of nerve impulses

-String of language units

Non-monotonic relationsThe changes in the acoustic parameters as the articulatory parameters vary

through ranges of values are often non-monotonic. The same type of relation is

also often observed between certain acoustic parameters and some aspects of the

auditory response to the different acoustic patterns.

ACOUSTIC-ARTICULATORY RELATIONSHIPSAccording to the source-filter theory of speech production,(Fant, 1960), the

production of speech sounds can be described as a process involving: The generation

of sound sources, and The filtering of these sound sources by the airway above the

glottis.

In the formation of vowel sounds the action of the glottis produces the basic source

of sound; this sound is then transmitted through the pharynx and oral tract to the

outside air. We can think of the tract as a filter that emphasizes some of the

components of the source sound, namely, those at or near the resonant frequencies

of the tract. Estimates of the acoustic consequences of changes in vocaltract shapes

lead to the following relation between tongue-body position and the first formant

frequency: vowel height is ____ correlated with F1 frequency.

ACOUSTIC-AUDITORY RELATIONSHIPSIt seems that not all items of acoustic information are equally important from

the point of view of speech reception. No doubt that the perception of speech is

necessarily structured by the inherent constraints of the auditory system.

Results from psychoacoustic studies have shown that the listeners sensitivity

to frequency changes is not the same across the frequency range. The auditory

system is more sensitive to frequency changes at lower than higher frequencies.

In addition, subjective auditory impressions of loudness differences do not

match sound pressure differences. For soft sounds , large changes in perceived

loudness result from relatively small changes in sound pressure, while for loud

sounds, relatively large pressure changes produce only small changes in perceived

loudness