Nature of Sound Hade PDF

Chapter 2: Sound: a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium Acoustic: branch of physics dealing with the generation, transmission, and modification of sound waves. Relating to the sense or organs of hearing, to sound, or to the science...

Chapter 2: Sound: a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium Acoustic: branch of physics dealing with the generation, transmission, and modification of sound waves. Relating to the sense or organs of hearing, to sound, or to the science of sounds. Psychoacoustics: the study of the relationship between sounds and their perception by the listener, especially with regard to how the perception depends on the. physical characteristics of the sound rather than on the mind of the listener. BASIC PHYSICS CONCEPTS The basic physics concepts that are relevant to the study of speech production and perception: Mass(m): is a fundamental property of an object that refers to the amount of matter in the obj. Force (F): is defined as any influence that causes an object to undergo a change in spd, dr, shp. Weight: is defined as the force of gravity on an object and is related to its mass. Volume: is defined as the quantity of three-dimensional space occupied by a liquid, solid, or gas. Density: is defined as mass of a substance, a material, or an object per unit of volume, or mass divided by volume. Speed:I s the distance traveled by an object in a given unit of time, measured in meters per second (m/s). Velocity: has the same numerical value as speed (m/s) but also specifies the direction of the movement. Momentum: refers to the mass time velocity of an object during motion, measured by kilograms times meters per second (kg-m/s). Acceleration: occurs when velocity changes as a function of time. The acceleration of an object is directly proportional to the force applied and inversely proportional to the object’s mass (m). Inertia: is the resistance any physical object to a change in its state of motion or rest.  Elasticity: is the property of a material that returns it to its original shape after it has been deformed by an external force. Stiffness: the mount of force required to displace the objectby some distance Work: occurs when a force is exerted over a distance and is measured in newton’s times distance in meters. Energy: is defined as the ability to do work. Forms of energy include chemical energy, electrical energy, thermal energy (heat),radiant energy (light), mechanical energy (movement) Power: refers to the rate of work done or energy used in a period of time and is measured in watts. Intensity: refers to power per unit of area and is measured in watts per square meter in the MKS system or watts per square centimeter in the CGS system. Pressure: is defined as force acting perpendicularly on a specific surface area. PROPERTIES OF SOUNDS Vibrations Frequency Intensity Duration VIBRATIONS: Vibrations: Sound is vibration of air particles produced by the vibration of an object or objects. A sound wave is the vibration of air molecules around their resting state following the disruption of the surrounding environment, which can be solid, liquid or gaseous. The vibrations of an object and the sounds produced by the vibration are affected by the properties of the object: Length Stiffness Mass Simple harmonic motion or oscillation: The simplest form of vibratory motion. The back and forth movement with its characteristic pattern of acceleration through the rest position and deceleration at the endpoints of the movement. Inertia and Elasticity The properties of inertia and elasticity are necessary for an object to vibrate. An object will remain motionless or inert, in resting state, unless some force acts upon it. Inertia: of an object is the tendency of the object to remain at rest or inactive unless disturbed by an external force. Elasticity: is restoring the force and it’s also the property of an object to be able to spring back to its original size, form, location or position, and shape after being stretched ( tuning fork). Condensation and Rarefaction Condensation : the resulting increased density, which results in an increase of pressure. Moves tympanic membrane inward slightly Rarefaction: the resulting decreased density of air in the area between the two groups of molecules, resulting in lower pressure. Moves tympanic membrane outward slightly Displacement Displacement:0ccurs when an abject is displaced from one point to another point. Simple harmonic waveform: is usually plotted over a time period of one or more cycles. Cycles: is movement away from one point and return movement to the same point in the same direction. Period: the time required for completion of one complete cycle of movement. Instantaneous Displacement, d(t): Describe the location of the vibrating at any given time or any instant. displacement is constantly changing over time. Displacement in a waveform is referred to as amplitude (distance) between the peaks of vibration. RMS amplitude is a third way of expressing amplitude of a waveform. - Peak Amplitude - Peak to Peak Amplitude - RMS amplitude Damping Damping: Decrease of vibration due to resistance. Is a decrease of amplitude. Forced Vibration: vibration will be maintained as long as a constant force is applied to the object to keep it in motion. Media for sound production Sound system: Source:anything that vibrates Medium:anything with molecules Receiver: anything that can detect vibrations - A medium is a necessary ingredient for the production of sound. Media, is plural of medium, include air, water, solid. - Sound occurs when a disturbance creates changes in pressure in air, water, or solid. Behavior of Air: - Air is a gas composed of: - Nitrogen (78%) - Oxygen (21%) - Traces of other elements (1%) including water vapor, carbon dioxide, and argon - Molecules are not stationary - But due to molecules thermal energy constantly move around in random pattern and at extremely high speed. -→ Brownian motion. FREQUENCY: Frequency: is one cycle of vibration which is one back and forth movement. Where the molecule moves to maximum distance from original spot , back to rest position, and moves to maximal point in the opposite direction and back again to rest position. refers to the rate at which an object vibrates and is measured in hertz (Hz). Frequency is objective measurement of a physical phenomenon. The frequency of sounds depends on: is influenced by properties of a vibrating object: - Length - Stiffness - Mass Categories of frequency: - Sine waves and Pure Tones - Phase - Wavelength - Resonance Sine waves and Pure Tones A sine wave or sinusoid represents a single frequency. Sine waves are commonly referred to as pure tone. A pure tone is a sound that consists of one single frequency (A single frequency tone). The sound wave, if we recorded it, would be a perfect sine pattern that repeated over and over with a given repetition rate. Phase Essentially, phase refers to sound waves. The first illustration below shows what happens when we’ve got two channels of a signal in phase. When both channels are in phase, we hear the sound at the same amplitude level at the same time in both ears. But if one side of the stereo signal is reversed, as shown in the third illustration, the signals will cancel each other out. In fact, if we were using a pure sine wave, combining both signals out of phase would result in silence,since the sounds would literally cancel each other out.  Wavelength The wavelength of a sine wave is the distance from some point on a sine wave to a second point 360 degrees after the beginning or the point at which the next cycle begins. The wavelength of a sound is related to its frequency. Speed of sound is a factor in the relationship between wavelength and frequency. Wavelength refers to the distance in meters or centimeters covered by one complete cycle of pressure change. Resonance Resonance frequency (fr): is also known as the natural vibration frequency of the object. - depends on the physical characteristics of the object: size, shape, length, density, tension, stiffness, as well as the volume of air enclosed within the object.length, density, tension, stiffness. Resonance: tendency of a system to vibrate with greatest amplitude in response to a frequency that matches or comes close to its own natural frequency. INTENSITY: Intensity: of a sound is related to the maximum displacement or the amplitude of a waveform. Force and Pressure Pressure: is defined as force acting perpendicularly on a specific surface area. Force: is defined as any influence that causes an object to undergo a change in speed, direction, shape. Pressure is a force exerted on an area, the amount of force and of sound pressure is directly related to the amount of vibration of an object, its displacement, and the velocity of the vibration. Pressure increases or decreases with changes in the strength and speed of the vibration. Units of Force and Pressure Dyne: is a unit of force commonly used in audiology and hearing science. A dyne in the amount of force required to accelerate 1 gm 1cm / sec2. Micro-Pascal (uPa): is a common unit of pressure and is a tiny fraction (a millionth) of Pascal. The minimum amount of force that is detected by a healthy young ear is approximately 0.0002 dyne/cm2 corresponding to a pressure of 20 uPa. Power and Intensity Power: refers to the rate of work done, or energy used in a period of time and is measured in watts. Intensity: refers to power per unit of area and is measured in watts per square meter in the MKS system or watts per square centimeter in the CGS system. The Decibel (dB) The decibel scale (dB) is designed to measure sounds that compares the amplitude and/ or intensity of any sound to a standard reference sound. The reference sound has an amplitude of 20 micropascals and intensity of 10-12 w/m2. Which it corresponds to 0 db. Sound pressure and Sound Intensity Sound Pressure – Indicates the amplitude level of sound at a specific location in space, and is a scalar quantity. The level is dependent on the location and distance the sound is observed relative to a sound source. Sound pressure is measured in Pascals. Sound Power – The rate at which sound is emitted from an object,independent of location or distance that the sound is observed.Sound power measurements are often specified in the noise regulations of many different kinds of products, from construction equipment to computer printers. Sound power is measured in Watts. Sound Intensity – Sound intensity is sound power per unit of area. It indicates the flow of sound through a specific area. Sound intensity is measured in Watts/m2. Calculation of Sound Intensities and Sound Pressure Measurement of Sound Calibration Different References for Decibels DURATION: the length of the time from the beginning to the end of a sound. - Dimensions of Duration -Onset: the initial portion of the sound -Rise time: it is defined as the time from the beginning of the sound at the baseline to the point where maximum amplitude is first reached. -Plateau: is the segment of sound during which amplitude is consistent or unchanging. -Fall time: It consists of the time required for the sound to decrease in amplitude from the maximum point to zero amplitude or back to the baseline. -Offset: the final portion of the sound. PSYCHOACOUSTICS: the branch of psychophysics involving the scientific study of sound perception and audiology—how humans perceive various sounds. More specifically, it is the branch of science studying the psychological responses associated with sound (including noise, speech, and music). Psychoacoustics is an interdisciplinary field of many areas, including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science. Pitch Perceptual correlate of frequency; when the frequency changes we hear different pitches. - Frequency is physical and pitch is perceptual. Just noticeable difference (JND): In the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable at least half the time (absolute threshold).This limen is also known as the difference limen, difference threshold, or leastperceptible difference. The just-noticeable difference (jnd) (the threshold at which a change is perceived) depends on the tone's frequency content. Below 500 Hz, thejnd is about 3 Hz for sine waves, and 1 Hz for complex tones; above 1000 Hz, the jnd for sine waves is about 0.6% (about 10 cents). The jnd is typically tested by playing two tones in quick succession with the listener asked if there was a difference in their pitches. The jnd becomes smaller if the two tones are played simultaneously as the listener is then able to discern beat frequencies. The total number of perceptible pitch steps in the range of human hearing is about 1,400; the total number of notes in the equal-tempered scale, from 16 to 16,000 Hz, is 120. Loudness Loudness, or volume, is the way that the human ear perceives sound. At its simplest, when the amplitude is increased, sound gets louder, and when it is decreased,sound gets quieter. - Amplitude is physical and loudness is perceptual. - Just Noticeable Difference (JND) for Intensity: is the minimum amount of change in a stimulus that can be detected. Using sound as an example, if a decibel level change from 60 decibels to 62 decibels is undetectable and a change from 60 decibels to 63 decibels can be detected, we know that at an initial stimulus of 60 decibels, a change of 3 decibels is the Just Noticeable Difference.  Duration Temporal Integration: Detection of sound is influenced by duration of the sound. Is used to describe the relationship between duration of sound and its detection by auditory system of the listener. - Just Noticeable Difference for Duration: Gap Detection: Used to describe the detection of a temporal interruption in a quasi-continuous sound. In people with normal hearing in laboratory situations, a gap of approximately 3 ms is just detectable. AUDIBILITY OF SOUND Minimal Auditory Field (MAF): is the threshold before which a tone cannot be heard by a participant. Participants are presented with tones in a sound field without wearing any headphones to better emulate hearing something in a real-life situation. The MAF is the threshold below which a tone or sound cannot be heard. Minimal Auditory Pressure (MAP): is the minimum level of a tone which can be presented via headphones to a participant at the minimum threshold of audibility. The MAP is the minimum level which a tone or sound can be produced and then heard by the participant, even when wearing headphones. Reference Equivalent Threshold Sound Pressure Levels (RESPLs): the sound pressure levels of pure tones at which an adequate number of young listeners without hearing loss just perceived the tones. PROPAGATION OF SOUND Speed of Sound: Sound travel or is propagated through a medium that is solid, liquid, or air. Speed of sound is defined by the distance the sound wave travels during a unit of time. 3 major factors influence the speed of sound through air: 1- Temperature  2- Moisture and humidity 3- Barometric Inverse Square Law: The intensity of sound decreases as sound waves travel farther from the source of the sound.The decrease of intensity of sound associated with the increased distance from the source of the sound. INTERFERENCE WITH PROPAGATION OF SOUND: Interference: incident and reflected waves are combining with each other. - Constructive interference (reinforcement): waves combine, reinforce each other and increase the resultant amplitude. - Destructive interference (cancellation): Waves combine and decrease the resultant amplitude. COMPLEX SOUND A complex tone is a sound wave that repeats with a given pattern BUT the pattern is not a sine wave. As we will see the complex tone consists not only of one frequency sine wave but rather a number of different frequency sine waves superimposed on top of one another (Two or more sounds of different frequencies).  - Fundamental frequency: the lowest frequency of the sound. The fundamental frequency of a voice is determined by the rate at which the vocal folds vibrate. - Harmonic frequency: frequency above the fundamental frequency Speech: is a highly complex sound. TRANSIENT SOUNDS Extremely brief sounds with durations of milliseconds or even a brief portion of just one millisecond are called transient sounds. NOISE - an unpleasant sound especially a loud one comprising of shouts too and is mostly undesired. - is characterized by irregular fluctuations of vibrations. Consist of two or more frequencies but the frequencies are not systematically related to each other. Types of Noise in Hearing Testing: - White Noise: - Narrowband Noise - Speech Spectrum Noise - Octave Band Noise Formants: The air inside the vocal tract vibrates at different pitches depending on its size and shape of opening. We call these pitches formants. You can change the formants in the sound by changing the size and shape of the vocal tract. Formants filter the original sound source. After harmonics go through the vocal tract some become louder and some become softer. Music: A music sound is characterized by a fundamental frequencycombined with harmonics, depending on the timber of the instrument.