Tonal sounds

Tonality refers to two types of sounds:

* *Tonal sounds*, which are more musical in nature, including melody, motif, and harmony
* *Atonal sounds* (also called non-harmonic sound), which resemble everyday sounds or noise – they don’t conform to traditional musical compositions

Sounds can be designed using tonal or atonal elements, and sometimes a sound will be comprised of both. Tonal sounds work best to communicate personality, emotion, and state changes, whereas atonal sounds better support motion transitions and express a sense of haptic feedback.

University of Michigan - Ann Arbor

Sound attributes can be adjusted in a variety of ways to create a specific effect.
* Representing sound 
* Timbre
* Tonality
* Dynamics
* Envelope
* Effects

Sound Attributes

People can discriminate changes in frequency between two tones by about 2 Hz for sounds up to 2000 Hz. Pitch relies on the subjective expereince of sound, which means frequency of sound is not the only determinant of pitch. There are two complementary ways that pitch information is encoded.

Encoding pitch information

Material Design Documentation

Sounds have measurable characteristics that can indicate how effective a sound will be at creating a desired effect. A technique that portrays these characteristics is called sound visualization. On a graph, the x-axis portrays one characteristic (such as time) and the y-axis portrays another characteristic (such as amplitude). In some cases, a characteristic is graphed using only a single axis.

These guidelines describe how sound can be visualized as a function of time, frequency (how high-pitched or low-pitched a sound is), or timbre (the character of a sound).

* Time
* Frequency
* Timbre

Representing Sound

The timbre of a sound describes its quality and character (without regard for its pitch or volume).

* Timbre types

Timbre

Tonality

In sound design, *dynamics* refer to changes in volume or loudness on either a micro scale (volume changes to a single sound) or a macro scale (volume changes to a set of sounds). 

Dynamic variation allows sounds to feel natural and realistic. Dynamic changes can highlight sonic moments of interest, create a sense of progress through a musical narrative, and give sound a natural quality.

* Examples

Dynamics

The envelope of a sound refers to changes in a sound’s amplitude over time. An envelope is comprised of many technical components, but the two most basic are the rise (*attack*) and fall (*decay*) of a sound.


Envelope

**Reverb** and **delay** are effects that can add a sense of space and depth. To keep sound effects from becoming too prominent a part of an earcon’s sound, they should be used sparingly.

The more reverb and delay a sound has, the more **wet** the sound is as opposed to dry.

Effects of sound attributes

The physical location of a sound can be distinguished based on the activation of receptors near the base of the cochlea and near the apex. Treble sounds vibrate at the base of the cochlea while basss sounds at the apex. Coplex sounds activate multiple areas of the cochlea with simultanious peaks of vibration along the basilar membrane. 

Place Coding

Directly encoding the auditory stimuli at the rate of auditory neurons. If there is a sound at 500 Hz, there will be neurons firing 500 action potentials per second. The firing is phase-locked to the stimuli, and the representation is averaged across ceveral cells. High-frequency sounds closer to the frequency of the action potential instead of the encoded auditory frequency.

Encoding multiple frequency allows the system to have higher than the maximal neural firing rate. 

Temporal coding

Audible frequency range is the span of sound frequencies a species can hear, and this range differs across species. In the textbook examples, chickens hear roughly $$125$$ to $$2000$$ Hz, mice hear roughly $$1000$$ to $$91000$$ Hz, beluga whales hear roughly $$1000$$ to $$123000$$ Hz, dogs hear about $$70$$ to $$45000$$ Hz, and cats hear about $$45$$ to $$64000$$ Hz.

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