Exam 1 Flashcards
What is needed to produce & transmit a sound?
A source (oscillations) such as a tuning fork and a material medium to conduct the oscillations such as air.
Frequency
of cycles*/second. Unit is Hz
(1 cycle = 1 compression + 1 rarefaction)
What range of frequencies can humans hear?
20 - 20,000 Hz
Equation for frequency & period
“Indirect” relationship
Absolute vs. relative units for sound intensity, pressure & power
Why is the relative decibel scale used instead of absolute scales?
- Absolute units deal with too large/small numbers
- The dB scale is a log scale, so big numbers are squeezed into smaller units
- Log 10 = 1; Log 100 = 2, Log 1000 = 3, Log 10000 = 4
Equation for dB (SPL)
- Pref = 0.0002 dynes/sq.cms (Lowest absolute sound pressure normal hearing subjects can hear at 1000 Hz)
- P = absolute sound pressure
Equation for dB (IL)
- Iref=10-12 watts/Sq.mts (Lowest absolute sound intensity normal hearing subjects can hear at 1000 Hz
- I= absolute sound intensity
Equation for wavelength
v = 340 m/s at 20º C
What is wavelength?
- Refers to the distance a sound wave occupies during one cycle of oscillation
- “Indirectly” related to frequency
In-phase vs. out-of-phase sounds & effect on amplitude
Pitch
- Psychological attribute corresponding with frequency (Hz)
- “Directly” related to frequency; higher freq. = higher pitch
- Unit is mels
Loudness
- Psychological attribute corresponding with sound intensity & pressure levels
- “Directly” related to sound intensity & pressure levels; higher dB = higher loudness
- Units are Sone & Phon
Pitch vs. Frequency Graph
We’re not that good at resolving frequency changes beyond 1500 Hz. Completely normal.
Equal loudness contour graph
- Hearing system is not very sensitive to hearing the very lows & very highs (dB SPL levels).
- For a sound at 100 Hz, you need a minimum of 40 dB SPL to hear it. At 30 Hz, you need almost 70 dB SPL to hear it. AT 1000 Hz, you only need 0 dB SPL.
Minimum Audibility Curve (MAC)
- Dark line on graph
- Shows that there’s more energy (dB SPL) needed to hear very low & high frequencies, and less needed for middle frequencies.
Threshold of feeling (on ELCG)
Top line: threshold of feeling/discomfort/pain. At this level, it doesn’t matter if it’s a very low/high frequency. We can still hear it.
Best volume for listening to music
If you really want to appreciate changes in frequency, you should listen at 50-70 dB. Here, you can isolate different frequencies & pick up pitch & loudness variations.
Best frequencies for hearing
- Relatively less energy (less dB SPL) is required to for frequencies between 1000 to 4000 Hz (these are most sensitive frequencies for hearing)
- More energy (more dB SPL) is required to hear very low frequencies below 500 Hz and above 4000 Hz
Simple sounds
- Have a single frequency of oscillation (ex: sounds from a tuning fork, pure tones from an audiometer)
- Have Simple Harmonic motion (SHM)
Complex sounds
Have multiple frequencies of oscillation (ex: human voice)
Complex periodic sounds
Have fundamental frequency (lowest pitch, maximum amplitude) and all additional frequencies are harmonically related to FO
(music, voiced speech sounds)
Complex aperiodic sounds
- No FO
- All additional freq. are not harmonically related to the FO
- Cannot assign a pitch
- Ex: voiceless speech sounds, white noise
Transient vs. continuous complex aperiodic sounds
- Transient: finger snap
- Continuous: waterfall
What does an audiometer do?
Generates pure tones
Spectral Analyzer
- Electronic device that performs a fourier analysis.
- Gives you a graph with amplitude on the Y axis and frequency on the X axis.
How do we generate periodic & aperiodic speech sounds?
- Air from lungs is source.
- If vocal folds are engaged, we produce a complex periodic signal.
- Vocal tract: VFs to lips (pharyngeal cavity, tongue, oral cavity, lips).
- All voiceless consonants we produce are aperiodic. Vowels & voiced consonants are periodic.
How are speech sounds modified beyond the vocal folds?
- A: Spectral analysis of the glottal pulse coming from the vocal folds. There is an Fo (right around 100 Hz, which would be avg. for male adult speaker).
- B: When sound passes through the vocal tract, it changes what comes out of it. Length of straightened vocal tract in avg. adult is 17cm. Resonating frequencies R 1-3 (peaks): frequency point w/ maximal amplitude.
- C: Output: interaction of glottal pulse + resonating frequencies of vocal tract. A + B = C. Energy levels close to resonating frequencies are enhanced & vice versa. Peaks are formant frequencies. All of the vowels that we produce sound different because the formant frequencies significantly change when the position of the tongue/lips changes.
Central suditory system structures
- Brainstem Auditory Nuclei
- Auditory Cortex of the Temporal Lobe
Peripheral auditory system structures
- Outer, Middle and Inner Ear
- Auditory Nerve
Peripheral auditory system functions
- Outer & middle ear collect & conduct sound energy
- Cochlea in inner ear analyzes frequency & intensity (Fourier analysis)
- Auditory nerve transmits electrical energy/spikes to the brain
Central auditory system functions
- Receive & Transmit Electrical Signals
- Responsible for:
- Localization
- Middle Ear Muscle Reflex Function
- Improved Speech Discrimination in Noise
- Auditory Memory
Temporal bone: petrous portion
- at base of skull
- houses essential organs of:
- hearing (cochlea & cochlear branch of 8th nerve)
- equilibrium (semicircular canals, vestibule, & vestibular branch of 8th nerve)
- houses internal auditory meatus, where 8th nerve exits
Temporal bone: mastoid portion
Posterior portion. You can feel the mastoid process. Contains mastoid air cells.
Temporal bone: squamous portion
Forms part of cranium. Contains EAM.
Temporal bone: tympanic portion
Forms base of ear canal.
Pinna/Auricle
- Works as an antennae
- Collects and transmits sounds to the External Auditory Meatus
- Helix: outermost rim
- Antihelix: innermost rim
- Tiny space at the top: triangular fossa
- Concha: deep cavity
- Tragus: little bump
- Lobule: lobe; no functional benefit in terms of amplification
Concha Effect
- Open concha area improves hearing for high frequency sounds (3-6000 Hz)
- 5000 Hz sound improved by 12 dB SPL on average
- Referred to as the resonance frequency related to the concha effect
External Auditory Meatus/Canal Structures
- Length = 24 mm/2.4 cms (Adults)
- Anterior 1/3= Cartilaginous (Wax producing glands and Hair follicles located in this region)
- Posterior 2/3 = Bony
External Auditory Meatus/Canal Functions
- Protective (Wax and shape of the EAM)
- Conductive (Transmit to the Middle Ear)
- EAM acts like tube open at one end and closed at the other end
- Provides Improved Hearing at 3 kHz (Referred to as the Resonance Frequency of the EAM). About 15 dB SPL at 3 kHz
