Perception of the sound has always remained the key element in the acoustic domain, in fact the very word acoustic means "sense of hearing". Since the so-called unwanted part of the Sound is called Noise, we shall include these two quantities together for this discussion on psychoacoustics which is about how a sound is perceived and appreciated.
There are quite a few ways to represent the sound as a value - Pascal is the base unit, represented in log scale (dB) and further added with filter notations of A, C and so on, however put together these indicate sound pressure / level in some way.
Frequency is another character that sound possess; in terms of physics, frequency carries the information of how many times the sound pressure particle is oscillating over its equilibrium position per given time, usually termed as cycles per second or Hz.
Combining the instantaneous change of sound pressure values and their inherent frequency information, a series of continuously varying sound or noise pattern form in the medium that it passes through and finally get perceived as a typical set of information by the auditory sensing system of humans.
While the change in pressure quantity along with its contained frequencies are a continuous modulation in time and space, so is the way its perception happens at the receiver end; the very way sound is created and the way it is perceived is broadly grouped under psychoacoustics.
A variety of terms come in play in psychoacoustics; the sound quality tools used for assessing the sound and its perception use many subjective terminologies such as tonality, harshness, roughness, articulation index, loudness, fluctuation index and many more; in abstract, these parameters are a combination of frequencies and their amplitudes formed in a particular sequence either at its source or at times in the receiver end.
The term "coloured sound" is one such process that is widely in use in the audio / visual industry; the sounds are created in a particular sequence with some delays, echos (reverbs) and at times with spatial attributes to make it more of an immersed experience of the visuals being cast together.
Human auditory system, in which the ear and its connected sensory organs are a typical Binaural configuration, is influenced by the head and torso anatomy for the way sound is perceived; the very location of outer ears on the skull with torso as base makes the ears to nearly have a 360* sound field.
Any incidence of sound is sensed with relative phase (time) delay between the 2 ears based on the spatial location of the sound source. This way the 3-D imagery is created by the brain to realise the depth, directivity and other characteristics of the sound. To further enhance this experience, synthesised sounds and their modulations are created and thus the psychoacoustics part of perception is initiated.
Finally, the sound and its perception are a complex combination of many factors beginning from its creation, boundary conditions, medium and the receiver. Psychoacoustics plays a significant role in how the sound is perceived based on all these variables.