Psychoacoustics
Within our principles of audio module we have covered the topic of psychoacoustics, this subject covers the aspects of sound which relate to our own human perception of the phenomena itself and the study of the psychological responses to sound which the listener experiences.
Covering the internal mechanics of how our ears receive auditory signal, the process involves the reception of sound waves from a source into the outer ear which gathers and directs the acoustic signal, where it is then directed down the auditory canal where natural occurring resonators are present, effecting the frequency response of our hearing perception to be more sensitive to specific bands of frequency which are the most resonant (1kHz - 4kHz).
At these stages the auditory signal is still in the form of acoustic energy traveling as air-pressure forming sound waves, until it reaches the middle ear section where it hits the ear-drum tympanic membrane and turns into mechanical energy by the vibration caused by the sound waves on the eardrum passing into the tiny bones it connects to which then link to the inner ear, converting it once again in the inner ear into electrical energy through the cochlea which the signal travels through. As they consist of tunnels of fluid either side of the basilar membrane, lined with hair cells which respond to specific frequencies as they go further up the cochlea, which in finally send the electrical signal to the brain and into our awareness.
When we hear sound there are many different aspects which we can distinguish which impart different subconscious preconceptions we may have of the source of that sound which occur simultaneously as we hear and process what we’re hearing. Firstly there is the source’s volume which can influence the perceived distance between the source and ourselves, louder equates to nearer, quieter to further. This can also be regarded as the loudness of a sound source and can be listed under a sounds dynamic properties; it’s intensity can effect whether we perceive a sound to be gentle or hard even though it has no physical properties to ascribe these terms with.
A sound source’s pitch can have great effect on the emotive response of a listener, as melody is a series of pitches a musician uses the various intervals, chords or lines in their repertoire to draw out those perceptive responses to create an effect through the music they’re performing, pitch being itself the human perception of frequency it is interpreted by our biology as a logarithmic scale as we perceive octaves as a harmonic interval drawn from the halving or doubling of an auditory frequency.
Timbre accounts for all the qualities of a sound which go beyond simply it’s volume and pitch, it is the sum of all the frequency information we receive from a sound source, as there are countless instruments there are also countless sounds which could come under the notation of middle C, and although all the same in pitch they would each sound very different from the rest due to their timbre, which the brain perceives and interprets to tell us whether we are listening to say a piano, a guitar or vocals.
There is lastly sound localisation which people perceive due to the fact that we have two ears receiving a stereo signal which can distinguish the direction of a sound source, a crucial piece of our evolution which in early human history was essential to our survival to find food, is now a property of sound utilised in immersive audio and 3D sound scape scenarios such as surround sound audio that tricks the brain into thinking a sound’s source is somewhere it is not. This is a common aspect to mixing which is utilised, known as panning, directional tweaks to audio are one of the most familiar effects and the reasoning behind it being understood that the separation of one source from others directionally makes it then clearer when we listen into it amongst other sound, a crucial method to allow audio tracks to sound less flat and more immersive.
