Second half of final Flashcards
Physical qualities of sound waves:
Amplitude: The magnitude of displacement of a sound pressure wave.
Intensity: The amount of sound energy falling on a unit area.
Frequency: For sound, the number of times per second that a pattern of pressure repeats.
Units for measuring sound:
Hertz (Hz): A unit of measure for frequency. One Hz equals one cycle per second.
Decibel (dB): A unit of measure for the physical intensity of sound.
Psychological qualities of sound waves:
Loudness: The psychological aspect of sound related to perceived intensity or magnitude.
Pitch: The psychological aspect of sound related mainly to the fundamental frequency.
Timbre: Psychological sensation by which listener can judge that two sounds that have same loudness and pitch are dissimilar, determined by the harmonic structure of the sounds.
Sine wave, or pure tone:
One of simplest kinds of sounds
Sine wave: Waveform for which variation as a function of time is a sine function
Time taken for one complete cycle of sine wave: Period
There are 360 degrees of phase across one period
Decibel (dB)
A unit of measure for the physical intensity of sound:
Named after the inventor* of the telephone, Alexander Graham Bell.
Decibels define the difference between two sounds as the ratio between two sound pressures: dB = 20 log10 (p1/p0)
Each 10:1 sound pressure ratio equals 20 dB, and a 100:1 ratio equals 40 dB
Doubling in sound pressure corresponds to 6 dB
*Bell actually just stole the patent [citation needed]
Pure tone
A tone with a sinusoidal wave form
Complex sounds
The summation of pure tones
Most sounds in world
Complex sounds can be described by Fourier analysis
A mathematical theorem by which any sound can be divided into a set of sine waves.
Combining these sine waves will reproduce the original sound
Results can be summarized by a spectrum
Harmonic sounds with the same fundamental frequency can sound different because amplitudes of harmonics here three different instruments.
Harmonic spectra: Typically caused by simple vibrating source, (e.g., string of guitar, or reed of saxophone)
First harmonic: Fundamental frequencylowest frequency component of the sound
First harmonic: Fundamental frequency
lowest frequency component of the sound
Timbre
Psychological sensation by which listener can judge that two sounds that have same loudness and pitch are dissimilar – defined by the shape of the harmonic spectrum.
Auditory system is acutely sensitive to natural relationships between harmonics
Harmonic
Harmonic spectra: Typically caused by simple vibrating source, (e.g., string of guitar, or reed of saxophone)
First harmonic: Fundamental frequencylowest frequency component of the sound
Timbre: Psychological sensation by which listener can judge that two sounds that have same loudness and pitch are dissimilar – defined by the shape of the harmonic spectrum.
Auditory system is acutely sensitive to natural relationships between harmonics
VOICES are HARMONIC SOUNDS!
If the Fundamental is taken away from a sound, people will still HEAR IT.
Interaural time difference (ITD):
The difference in time between a sound arriving at one ear versus the other.
Medial superior olives (MSOs): First place where input converges from two ears.
ITD detectors form connections from inputs coming from two ears during first few months of life.
Azimuth
Used to describe locations on imaginary circle that extends around us, in a horizontal plane
Let’s analyze ITD:
Where would a sound source need to be located to produce maximum possible ITD?
What location would lead to minimum possible ITD?
What would happen at intermediate locations?
Medial superior olives (MSOs)
First place where input converges from two ears.
ITD detectors form connections from inputs coming from two ears during first few months of life.
Interaural level difference (ILD):
The difference in level (intensity) between a sound arriving at one ear versus the other.
Lateral superior olives (LSOs): Neurons that are sensitive to intensity differences between two ears
Excitatory connections to LSO come from ipsilateral (same side) ear
Inhibitory connections to LSO come from contralateral (opposite side) ear
ITD and ILD compared:
Low frequencies are diffracted by the head (like an ocean wave around a pylon), high frequencies are absorbed.
Low Frequencies / Timing Cues Dominate
High Frequencies / Intensity Cues Dominate
Stimuli on headphones, where ITDs pointing to the left are offset by ILDs pointing to the right, so the sound is perceived as coming from the midline.
Low Frequencies
Timing Cues Dominate
High Frequencies
Intensity Cues Dominate
Subwoofer placement is less important in a home theater setup due to our inability to accurately localize the low frequencies.
…
Cone of confusion
Regions of positions in space where all sounds produce the same time and level (intensity) differences (ITDs and ILDs)
Experiments by Wallach (1940) demonstrated this problem
THE MOST CONFUSION CONE:
ABOVE-infront-below-behind!!!
Directional transfer function:
Shape and form of pinnae helps determine localization of sound
Describes how pinnae, ear canal, head, and torso change intensity of sounds with different frequencies that arrive at each ear from different locations in space (azimuth and elevation)
Sometimes called Head-Related Transfer Function
BINAURAL RECORDINGS
Recording through microphones inside your head, near the ear drums
Direction transfer function preserved. Then you feel sound as coming from outside of your HEAD!!