Some years back while mixing and mastering an album..in attempting to setup my listening room and to calibrate my monitors...I starting with a more quantified approach using audio visualization tools that were available from the Internet... I calibrated my monitors and identified frequencies that were dropped out by recording white noise with various microphones and found the sweetspot in the monitor field...in doing so I stumbled into looking at full songs and vocals and I made a observation that I felt was astounding...I analyzed numerous hit songs by running the song through a visualizer that produced a sonogram...I picked vocal artists who had a quality of voice that I found pleasing to listen to and were hit song singers...
I also analyzed some tunes that were great musically but lacked that vocal sparkle.
What I found is that great singers produce a sonogram that shows significant instrument like qualities with several bands of semitones working together to make the actual note sung very rich and full of harmonic vibration and natural dissonance....a thin voice is just that...it lacks the semitones or they are unevenly distributed semitones that accompany the main frequency of the note sung. When the voice lacks a instrument like sonogram...the voice is unpleasant. Of the voices that were the most rich, Mahlia Jackson had several evenly distributed bands of frequencies accompanying the base note both above and below. The distribution of the semitones led me to assume they were near perfect overtones and harmonies that to our ears made the voice sound full and rich. Even Bob Dylan showed the pattern...despite his broken, breathy, nasal singing style his sonogram was rich with character. I thought for sure his would not.
On hit songs from a variety of genres and eras one thing that stood out was the vocals exhibited the same semitone patterns...in varying degree...most amateurs simply do not have this. I though it might of been tape saturation of vocal effects processing but after looking at raw digital vocal tracks from accomplished vocalists those tones were present on unprocessed tracks.
For comparison I also looked at various instruments...cello, violin, saxophone and guitar and it was shown that the semitones were very pronounced and quite numerous above and below the base frequency....one of the tools I used was a simple iTunes visualizer plug-in that provide a horizontal real-time scrolling image of the music. I simply watched the music with a tool that biologists used for analyzing bird calls and various other sounds of nature.
from this analysis I determined a few things, 1. That my own voice is not pleasing. (lol) 2. The music and sound operate on our brains and in a very complex manner and that our ears and brain are perfectly adapt at understanding the sound of music (no pun) at a very minute level of detail. So the structure of a song, key and tempo I believe is simply a coincidence and if you look at the the vocalist and the character and quality of the voice as well as the sound and tonal balance of the instrumentation, that has a very huge influence on our acceptance of one song over another.. What was interesting is that great vocalists seem to be able to control the number of semitones produced and do so to illicit maximum emotional effect in the song itself...which is the artistry and talent of the musician to take the listener beyond simply listening and to create an emotional response..
All in all my few weeks of dorking around with sound from various instruments, vocal tracks, songs and tone generators I came away with a new found appreciation of great music and how special the people are that make music...and that we separate and celebrate these people and their ability because it is a very rare gift indeed.