At your risk.
Music deals with vibrating molecules. for example of the metal piano string, or the vibrating molecules of air which will also hit the ear drum of the listener to create the sensation of hearing in the listener's mind.
Electronics deal with the corresponding vibration of electrons. For example inside the copper wire of a cable which carries the music of a symphony or a beautiful song.
A microphone converts the vibration of air molecules to a corresponding vibration of electrons in the cable at the output of the microphone. The microphone preamplifier will magnify or amplify these vibrations.
The cause of making the air molecules to vibrate in turn travels at the speed of sound in air, the speed of sound in air. The cause of making the electron vibrate in turn inside a wire travels at the speed of light in the metal of this wire. The speed of the light or electromagnetic wave in this metal.
It would seem correct to assume that a perfect sound system would convert exact replicas of the molecule vibration to the electron vibration.
More than often this is not true especially in popular music where the sound reproduction is louder than the moment a singer sings to record.
A reason for this is that the sensitivity of the human mind to frequency is also a function of intensity. For example for soft sounds a bass guitar needs to be as much a s a million times, that is 60db more powerful than a flute (mid range note) in order to sound as loud.
But when higher intensity is involved the sensitivity of the listener's mind to bass frequency becomes much closer to the sensitivity to mid frequencies for a similar sensation of loudness.
The curves that describe this phenomenon are called Equal Loudness Curves.
Due to the fact that the frequency response curve of the human hearing mechanism depends on intensity it may be trivial to assume that for perfect recording and reproduction we need flat frequency response from microphone of singer to the loudspeaker of listener.
It is more appropriate to consider flat frequency response from record producer mind to the listener's mind.
For example a singer reproduced at higher level than while recording will sound bass heavy.
In addition the frequency spectrum of a singing voice depends on effort when singing. For example when a singer sings softly the bandwidth of the voice is much higher with an increase in bass and high frequency content than when singing loud where most energy is concentrated on mid frequencies.
This would make a softly sung melody sound even more bass heavy when reproduced at a higher level.
To make such a situation sound correct to the listener's mind is not only a great work of engineering but also a great work of art.
For example Suzan - Leonard Cohen
(A loudspeaker or headphones convert electron vibration back to air molecule vibration so that we can listen to the beautifully made example below):
Further Reading:
Sound and Hearing - S.S Stevens, F. Warshofsky - Time Life Encyclopedia
Sound Picture Recording and Reproduction Characteristics - D.P. Lowe, K. F. Morgan - Journal of the society of motion picture engineers
Elements of Sound Recording - Frayne, Wolfe
https://en.wikipedia.org/wiki/Equal-loudness_contour
