THEORY OF AUDIO Flashcards
WHAT IS THE FIELD OF AUDIBLE SOUND?
-between 16,000 Hz to 20,000 Hz
-20Hz to 20kHz
-mechanical energy in the form of pressure fluctuations in an elastic medium
WHAT IS ACOUSTICS?
-the wave of mechanical energy transported through a medium
WHAT IS ULTRASOUND?
- sound with frequencies higher than 20,000 Hz
- higher than 20 kHz
WHAT IS INFRASOUND?
-sound is lower than 20 Hz
WHAT ARE WAVES LIKE IN LIQUID AND GASEOUS STATES?
-progressive longitudinal waves
(particle displacement parallel to direction of wave propagation, particles oscillate back and forth between their equilibrium)
WHAT ARE WAVES LIKE IN A SOLID STATE?
-progressive transverse waves and longitudinal waves can occur
HOW ARE SOUND WAVES DISTORTIONS?
-they do not transport environment particles only their oscillating movement
WHAT ARE THE SPEEDS OF SOUND IN DIFFERENT MEDIUMS?
-slowest in gases, faster in liquids, fastest in solids
WHAT IS SOUND PRESSURE?
- sound pressure, or acoustic pressure (p),
is the local pressure deviation from the ambient (equilibrium) atmospheric pressure, caused by a sound
wave
-max speed will have a max pressure
-lowest value of air sound pressure = 2.10^-5 Pa
-The Sound Pressure Level (SPL) is a logarithmic scale of sound pressure (p) defined relative to a reference sound pressure that is approximately the sound pressure of a 1000 Hz sinusoid that is just barely audible; its unit is dB (decibel):
L = 20 log (p/p0), where p0 = 2 x 10-5 Pa
WHAT IS SOUND INTENSITY?
-the energy that passes through the unit area perpendicular to the direction of sound per unit time (W/m(squared))
-threshold of hearing = 1x10^-12 W/m^2
-proportional to the square of the amplitude of the sound wave
-as sound waves travel away from their source, the energy is spread over a greater surface area causing a reduction in the intensity of the sound wave
WHAT ARE THE DIFFERENCES BETWEEN TONE AND NOISE?
A tone is a single frequency and is regular and periodic (vocal cords), while a noise is a single tone or a collection of tones and is irregular (drums)
WHAT FREQUENCY OF SOUND IS IMPORTANT FOR SPEECH INTELLIGIBILITY AND WHICH THE EAR IS MOST SENSITIVE TO?
-2 to 4 kHz
WHAT IS THE DYNAMIC RANGE OF THE EAR?
-in the middle of the audible frequency range of about 120dB
WHAT IS FREQUENCY MASKING?
-the inability to hear two tones when they are playing simultaneously
WHAT IS THE SOUND WAVE?
-the pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water or any other liquid or solid matter) as it propagates away from the source of the sound
-require a medium to transfer energy
WHAT IS PITCH OF A SOUND?
-an auditory sensation of a frequency
-depends on frequencies
-frequency is objective but pitch is subjective
-human brain determine pitch of a sound wave, it doesnt actually have one
WHAT IS TONE COLOUR / TIMBRE?
-the quality of a sound that distinguishes it from another
-determined mainly by its frequency spectrum
EG: difference between guitar and piano playing the same note
WHAT IS SOUND VOLUME?
-subjective term
-the determination of the sound which sound waves act on the pitch
WHAT IS SOUND INTENSITY?
-objective term
-sound power per unit area
-lowest value corresponds to the sound intensity threshold of hearing (0.00001 Pa), the highest sound intensity determines the threshold of pain (100 Pa)
-dynamic range of human hearing is 120dB
L= 10 log (I/I0), where I0 = 10-12 W/m2
-measured in dB HL (Thresholds below 20 dB HL are considered in the normal range, while thresholds above 20 dB HL are reported as the hearing loss (mild, moderate, severe or profound)
WHAT IS THE DOPPLER EFFECT?
-changes in the frequency of any sound or light wave produced by a moving source with respect to an observer
EG: ambulance siren being so loud when past you but quiet as it goes further away from you
COMMON DECIBEL LEVELS
WHAT IS THE WEBER-FECHNER LAW?
-perceived intensity is proportional to the logarithm of the stimulus
WHAT IS FREQUENCY?
-how often the vibration repeats
-expressed in Hz cycles per min
-distinguishes mechanical waves (infrasound, ultrasound, ultrasonic)
-at constant speed of propagation - wavelength is inversely proportional to frequency
(waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths)
-objective
WHAT FORMS THE OUTER EAR?
-pinna and auditory canal
-role is to bring the soundwave to the eardrum at the end of the auditory canal
-role of the pinna is the reflection and focusing of the incoming sound wave to the auditory canal
-tympanum is the closed end of the eardrum which enhances the sound frequency range of 2-5kHz by its resonance
-air filled