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sound
auditory sensation in the ear
What is the study of sound?
acoustics
sound wave
carries information or energy from one point to another
sound wave
carries information or energy from one point to another
Two types of waves
longitudinal and transverse
longitudinal wave
compressional wave, sound in air
transverse
direction of wave is perpendicular to the propagation of the wave
Frequency (audible) range of a sound wave
20 Hz to 20 KHz
What happens to polarity if a wave pulse on a string is reflected from a fixed end? a free end?
polarity is inverted; reflects the wave
progressive/ traveling wave
consists of a disturbance moving from source to surrounding place, transferring energy
Standing Wave
A wave pattern that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere
superposition of a wave
constructive/destructive, add or subtract amplitudes
Wave Interference
Two waves collide to create large or smaller wave
wave propagation
the way a wave travels
Wave lengths and doppler effect:
Longer wavelength: when the sound moves away from you- lower pitch Shorter wave length- when sound moves towards you- higher pitch
wave reflection
wave hits barrier and reflects back with little energy loss
wave refraction
wave hits barrier and reflects back with energy loss
diffraction
low frequency waves diffract more than high frequency waves
resonance
the response of standing waves to others of the same frequency
partial harmonics
waves in sound that are integer multiples of the fundamental frequency are of decreasing energy as distance grows from the fundamental frequency
Overtones/partial
all of the tones over the fundamental frequency. Partials: Includes fundamental frequencies, but overtones do not.
acoustic impedance
Opposition of flow of energy
Sound pressure
changes in air pressure due to the passage of sound energy
Outer Ear
- pinna - external auditory canal Ear Drum
middle ear
-Oval window -eustachian tube -auditory ossicles Regulates ear pressure
Inner ear
-cochlea functions in hearing and balance; filled with fluid
place pitch theory of pitch perception:
freq=distance traveled on basilar membrane
critical bands
frequency regions in cochlea need to recognize a separation in the brain btw frequencies
a critical band for a given frequency is:
-100 Hz below 500 Hz -10%-20% of the frequency above 500 Hz
Masking Sound
when to separate sources of sound are perceived simultaneously, obscuring each other
psychophysics
the measure of stimulus strength and sensitivity to the stimulus
Fourier analysis breaks up complex tones into 2 things:
fundamental frequency & harmonics
fourier synthesis
adds amplitudes of waveforms
pure tones with slightly different frequencies are:
beats/rough tones
when two pure tones are within 15 Hz of each other we hear:
the difference in freq. btw the two and the average pitch
when two pure tones are greater than 15 Hz but less than the limit of freq. discrimination:
we hear a rough tone and the average freq.
when two pure tones are greater than the limit of freq. discrimination:
we hear them as individual tones
combination tones
when 2 loud tones are sounded together, a 3rd tone is heard thats not actually present in the audible sound
Dissonance
Uncomplimentary tones; disharmonious, builds tension
consonance
repetition of final consonant sounds
all western scales use the:
octave
pythagorean scale
based on intervals of fifths
equal temperament
12 pitches per octave
What instruments are in the brass family?
trumpet, cornet, trombone, tuba, French horn, etc.
oscillations in a pipe
variations of phase and amplitude
which family has a mouthpiece and a bell?
brass
white noise
all frequencies with each frequency having the same amplitude
phoneme
smallest unit of speech
formants
frequency regions of phonemes where harmonics have high amplitudes
speech sounds can be analyzed using:
spectrograms
spectrogram
graph of frequency (y-axis) as a function of time (x-axis)
Direct current
electrons flowing through a wire in a single direction
volt
unit of energy per unit charge
basic unit of current
Amp
alternating current
voltage that changes in a sinusoidal manner
effective voltage
the ac voltage that would have the same effect as a dc voltage
dynamic loudspeaker
has a cone and voice coil, current flows through coil which moves due to Faraday's law
electrostatic speaker
conductors on outside separated by an insulator, when voltage is applied it bends which moves air and creates sound
shortcoming of a speaker
sound from the back will interfere with sound from the front causing reduced response
Three basic types of enclosures
infinite baffle, acoustic suspension, tuned port/bass reflex system
loudspeakers in general have limited ranges of:
frequency response
woofer
a loudspeaker designed to produce a low-frequency sound
Tweeter
A loudspeaker designed to produce high frequency sounds
how are electrical signals from the amplifier split up and how are they sent to the correct speaker?
split up by frequency and sent to the correct speaker by a crossover circuit
microphone
converts sound pressure or sound velocity to a voltage
what are the two ways in which microphones are classified?
-type of transducer -directionality
electromagnetic microphone
voltage generated by motion of conducting coil, voltage output is low and must be amplified
piezoelectric microphone
voltage generated by squeezing a crystal, has high output impedance
Condenser Microphone
high quality mic that can be very small and is generally powered by phantom power or a power supply
bidirectional microphone
most sensitive to the front and back
unidirectional microphone
most sensitive to front
omnidirectional microphone
equally sensitive in all directions, "perfect"
analog to digital converter
converts sound waves into digital signals
digital to analog converter
converts digital data into voltage/electric charge
how many digits do binary numbers have? digital?
2 (0 and 1); 10
how many bits make a byte? a nibble?
8; 4
Lossy and lossless
-Lossy: can't restore file to original state (usually media) -Lossless: can restore file to original state (usually text files)
what type of recording to compact disks use?
16 bit recording
Nyquist Criteria
Minimum sampling rate (2*max frequency)

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