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1. Sound is Kinesthetic

Like touch, hearing is a form of mechanosensation. Hearing sound is not much different from when a person taps you on the shoulder or the wind against your body, and any sound may illicit a movement response, whether it is a piece of music or a loud noise. Producing natural sound requires movement, whether vocally or using an instrument or object.

The outer ear is comprised of the pinna or auricle, having many folds and curvatures, and the ear canal, which leads to the ear drum. The outer part of the ear canal is made of cartilage and is also fibrous, being a continuation of the cartilage of the pinna. The inner part of the canal is bony.

The middle ear consists of the tympanic membrane or eardrum. Central to the middle ear is a small air filled chamber, the tympanic cavity. Inside the chamber are the ossicles, the three smallest bones in the body. These bones are called the malleus, incus, and stapes, sometimes referred to as the hammer, anvil, and stirrup. These bones aid in the transmission of sound to the inner ear from the eardrum. Vibrations from the ear drum are converted into pressure waves in the fluid of the cochlea through the oval window. The vibrations may be amplified up to 20 times that of what they were at the ear drum. The vibratory area of the ear drum is 14 times larger than that of the oval window.

The inner ear consists of the cochlea, which is spiral shaped and filled with fluid. It is divided by the organ of Corti, which is the means by which neural signals are sent to the brain. Inside this organ is the basilar membrane, which vibrates when waves propagate the fluids through the oval and round windows connected to the middle ear. Each ear has around 15,000 hair cells. Frequencies are picked up at unique locations along the basilar membrane, with movement of the hair cells on the membrane causing them to become depolarized by the fluids and adjacent hairs. The depolarization causes the hair cells to release neurotransmitters and an electrical signal is sent to the auditory nerve and auditory cortex. The range of human hearing is around 20 Hz to 20 kHz. The threshold of pain is around 120 dB.

2. Sound is Spatial

Hearing sound lends the sound to a particular location in perception, not unalike vision, though much less precise, as one may visualize a sound source with their eyes closed.

The distance between ears causes a time delay which allows us to determine the location of a sound horizontally, and how far away it is. Additional locational information is gathered by the frequency response or filtering by the ear itself allowing us to determine the vertical location, and perhaps if it is in front or behind.

3. Timbre Allows us to Distinguish Unique Sounds

Timbre allows a person to identify and isolate a sound from others. A unique timbre may be associated with a location in perception though it may come from the same location – as in front of or behind another sound, or be perceived as having spatial aspects – shape or form, and even color in certain individuals.

Timbres that are similar to speech will induce responses from the part of the mind that uses language and identifies words and grammatical structures.

4. Sound is Time-Based

Individual events heard less than around 50 milliseconds apart will be perceived as one event, otherwise they will be perceived as separate events. The type of wave and sound will effect the delay time it takes to perceive separate events. Pops and clicks may be very close to each other and perceived as separate events. This effect may be related to the range of hearing as the intervals within the frequency range of hearing will be perceived as one sound; a 50 millisecond delay is the length of a 20 hertz wave.

Rhythms may lend themselves to perceptions of cycles within the body, such as breathing in phrases or heart rate as tempo. Tempos usually do not drop below 40 beats per minute or go above 200 beats per minute – a slightly extended range of heart rates.

5. Sound is Pitch-Based

Frequencies in sounds with tone qualities lend themselves to pitch perception. Different pitches are picked up at different locations in the cochlea of the ear.

Pitch may be associated with a spatial location. In general these are in a range from low to high. In certain individuals pitch may be associated with color, though unique colors associated with specific pitches are not agreed upon.

Frequencies that are played together out of tune or out of phase produce beats in which the amplitude rises and falls. Phases are related to the localization of sound as a given sound will reach each ear at a slightly different time. This is similar to how stereo vision works, and many interesting stereo effects in audio can be achieved by using slight delays. Beats may produce the effect of a third tone in binaural beats.

Melodies may be strongly related to memory. They may both cause memories to arise, and be remembered easily. Predictable melodies such as scales may produce perceptual effects for expected notes, such as filling in gaps of expected notes when another sound is played that would mask the predictable pattern.

Combination tones may result from a missing fundamental, or when the harmonics of a fundamental are produced by two other notes without the fundamental itself.

An object will resonate with a frequency dependent on its width or length. The body has its own resonances, and those within the throat, mouth, nasal cavity have been used in making music with timbres having rich harmonic content.

Individual ears may localize sound as the shape of the ear effects frequencies reflected, and different points and positions may reflect different frequencies. Cupping one’s ear in various positions is all that is necessary to hear the differing frequency response. Amplitude also effects distance perception and this is effected by the external parts of the ear.

As an object or the head moves the frequency response changes in the perception of a single ear, and this change in filtering of frequencies can be compared to the initial position. The mind is perhaps acclimated to a regular frequency response resulting from reflections inside and outside the ear, and when altered, can be tricked into thinking a sound is coming from somewhere else.

Because individual timbres tend to be associated with overtone qualities and locations, pitches that are harmonically related may attain a location of their own within the mind of the listener, and if pitches are shared between these chord locations, when the chords modulate to those nearby, a change in location may be perceived. When many pitches are played rapidly and successively in different registers while moving through keys, the pitches may be perceived as coming from different locations, and not merely as high and low. This is a new possibility for the relationship of pitch and spatial location.

6. Polyphony Has Many Possible Effects

Harmony is a result of physical properties of sound, as multiple pitches within the harmonic series will produce consonances, and those higher in the harmonic series will be perceived as being dissonant. Harmony may also be present in color, and as notes correspond to others harmonically in a relative manner by interval, such may be the case with color; colors opposite each other or those that produce neutrals may produce the sense of color-dissonance.

Consonances and dissonances in music are strongly associated with emotions. The minor third in speech reflects its use in music as an interval that communicates sadness. Various chords and successions of chords tend to produce feeling.

Many types of canon exist in counterpoint: mirror, table, retrograde, crab canon in which the same material is altered or produces effects in its repetitions at different starting points and intervals.

Ostinato and droning are commonly used in many cultures. This may produce the effect of a central location or tonality.

7. Sound is Attention-Based

A single melodic line produced by one timbre may be perceived as two or more while in different registers, and indistinguishable if each note is put in a unique register in a technique called pointillism.

Multiple lines produced by different timbres may be perceived as a single melodic line, if the line produced by both timbres in combination is predictable. They may alternate between the impression of a single line and multiple lines dependent on tempo and the complexity of the melody. This can be achieved by a technique called hocketing, in which two lines alternate between the dominant notes. Hockets are more apparent if they are panned or from different sources, and may be recombined into a single line. Hockets can be composed by writing a melody first and then dividing it into separate parts.

The mind tends to follow predictable patterns of rising or falling notes in a scale one after another or continuously rising or falling sound. As one sound continues to rise, another may be introduced in a lower register undetected until the other is out of the range of hearing.

The mind tends to want to pay attention to one line at a time, and when two lines alternate between notes played at the same time and notes played between the others, the mind has choices of which information to pay attention to.

8. Sound Induces Emotions

This aspect of music and sound is highly subjective, and which songs and pieces produce emotions in different individuals varies.

Basic harmonic sonorities tend to be associated with happiness or sadness, and more subtle and complex harmonies and progressions with other feelings, becoming more subjective depending on their complexity.

Different modes tend to illicit different emotional responses.

9. Sound Creates and Uses Memories

Everybody has had the experience of a song getting stuck in ones head – perhaps because they do not know how it ends.

The memorization and learning of musical material has been shown to increase learning abilities in other areas.

Sound may cause images and memories to arise within the mind.

10. Sound and Music are Universal

Sound is closely related to language and the formation of words and meanings.

Sound is closely related to vision as it uses spatial information, and to movement as it is highly kinesthetic in nature.

Sound is related to learning and all other subjects.

To which extent perfect pitch and other musical abilities are learned is debatable.

Categories for Auditory Illusions

Replacement, masking, expected notes

Localization using pitch, timbre, harmonics

Contour confusion, up and down scales and repetitions

Stereo confusion, left and right bouncing back and forth

Otoacoustic emissions

Speech, timbre fragmentation and reorganization