Treble is an aspect of pitch. It is the experience of high-frequency sounds. This is often used when explaining musical sounds, though it also talks about the locational vibration of the basilar membrane at the base of the cochlea.

Sound: treble

Bass is an aspect of pitch. It is the experience of low-frequency sounds. This is often used when talking about musical sounds or instruments, though it also talks about the locational vibration of the basilar membrane at the apex of the cochlea.

Sound: bass

In practice, pitch perception is explained by a combination of the temporal and place theories, with their respective contributions depending on the sound's frequency. For frequencies up to approximately 4000 Hz, both the firing rate of neurons (temporal cues) and the specific location of stimulation on the basilar membrane (place cues) work together to determine pitch. However, for frequencies above this 4000 Hz threshold, pitch is encoded exclusively through place cues.

Hybrid Model of Pitch Perception

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. 

Grinnell College

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

The place theory of pitch perception proposes that pitch is determined by the specific location on the basilar membrane that is most stimulated by a sound wave. According to this theory, different frequencies activate different areas of the membrane. Specifically, the base of the basilar membrane is most sensitive to high-frequency sounds, while the tip responds best to low-frequency sounds. Consequently, the hair cells located in these distinct regions function as specialized pitch receptors: those at the base are considered high-pitch receptors, and those at the tip are considered low-pitch receptors.

Place Theory of Pitch Perception

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

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

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.

Tonality

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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