Psychoacoustic concepts
"Psychoacoustics, is the study of things like hearing thresholds, loudness, just noticeable differences, masking, and localisation.”
(Martin 2011)
Let’s break this down to its break this down so we can better understand its relevance to song analysis. To do so we only really need to understand the hearing thresholds, loudness and localisation aspects.
Hearing thresholds
The human ear has a frequency range of from roughly 20Hz to 20kHz. This threshold changes as we grow older and with exposure to loud noises. On an interesting note although frequencies above 20kHz are not perceived by the human ear. However, for example a 25kHz harmonic on a stringed instrument can have and effect on the perceived timbre of the sound. (Blackmere, 2012)
(Adminofthissite, 2012)
Understanding this threshold, we should take steps to ensure the best possible listening environment. This includes speakers and headphones with a flat response curve. When analysing any piece of music I use at least 2 sources mostly my reference monitors KRK VXT4's and reference Sub KRK S10, I also utilise my Audio-Technica ATH-M70x reference headphones. These both have relatively flat response curves and give me the truest representation of sound I can afford.
Here is the frequency response curve for my monitors.
(Decks.co.uk, 2017)
Loudness
"Loudness is a psychological term used to describe the magnitude of an auditory sensation."
(Fletcher & Munson, 1933, p. 82)
The human ear is an interesting piece of the human evolution. We have an amazing ability to hear sounds. However, we don't hear all sounds equally. Harvey Fletcher and W. A. Munson in 1933 did the first psychoacoustic research into equal loudness which found we perceive volume differently for different frequencies at different amplitudes (see below).
(Martin, 2011)
This research allows us to understand how the human ear reacts to different frequencies. When analysing music or audio it is important to keep this in mind as perceived loudness in a 50Hz tone requires a greater amplitude than the equivalent "loudness" at 3kHz. The red line on this graph represents the threshold at which sound is perceived at all.
Localisation
Understanding what sound is playing and how loud it is is part of the battle when analysing a piece of music. To fully grasp sound we must also understand its direction in a virtual stage. In everyday life we hear sounds all around us. If a sound hits our left or right ear first we perceive it as coming from that side and if a sound hits both ear simultaneously it is coming from the front. Music uses these techniques to give us a virtual sound stage and if we can understand how we perceived the sound we can rather accurately determine its location.
(Mark AndersonAudio, 2016)
References:
Adminofthissite. (2012, October 2). 20Hz to 20kHz (Human Audio Spectrum) [Video file]. Retrieved from https://www.youtube.com/watch?v=qNf9nzvnd1k
Blackmere, D. (2012). The World Beyond 20kHz. Retrieved from http://recordinghacks.com/articles/the-world-beyond-20khz/
Decks.co.uk. (2017). [VXT4-FREQUENCY-RESPONSE]. Retrieved from https://www.decks.co.uk/products/studio-monitors/krk/vxt4
Fletcher, H., & Munson, W. A. (1933). Loudness, Its Definition, Measurement and Calculation. The Journal of the Acoustical Society of America, 5(2), 82-108. doi:10.1121/1.1915637
Mark AndersonAudio. (2016, August 17). Interaural Time Difference and Interaural Level Difference [Video file]. Retrieved from https://www.youtube.com/watch?v=7-tJoSS5fmg
Martin, G. (2011, October 23). Physiological acoustics, psychoacoustics and perception. Retrieved from http://www.tonmeister.ca/main/textbook/intro_to_sound_recordingch6.html