In the diagram below, you can see how the tongue and the lips can alter the shape of the oral cavity and thus change the spectrum of the produced sound.
The two singers here are Vladimir Pasuikov and, with an even lower voice, Yuri Wichniakov, one of the most famous Basso Profondo, who are unique to Russian singing. Their vocal range is at least one octave below the normal bass range (think Paul Robeson). In the first extract the bass hits the low Ab1; in the second the bass hits a G1. Not only do they possess the lowest notes of any choral singer, but the soloists have such full voices that the effect is immediately striking.
Radu Marian singing LASCIA CH’IO PIANGA
Prof. Andrea Angelini, Italy The Quality REGISTERS
Head, Chest, Shoulders, Knees and Toes!Sounds may be generally characterized bypitch, loudness, and quality. Sound "quality" or"timbre" describes those characteristics of soundwhich allow the ear to distinguish sounds whichhave the same pitch and loudness.
What is the timbre?Timbre is then a general term for thedistinguishable characteristics of a tone. Timbreis mainly determined by the harmonic content ofa sound and the dynamic characteristics of thesound such as vibrato and the attack-decayenvelope of the sound.
HarmonicsThe spectrum of the sound produced by ourvocal chords is changed by the resonances of thedifferent harmonics in the cavities locatedbetween the vocal cords and the outside: thepharynx, the mouth and the nasal cavities.Depending on the form of these cavities, certainfrequencies will be faded while others will beamplified and will be more audible. The areaswhere the harmonic frequencies are amplifiedare called formants.
The first formantThe detection of the first formants allows us todistinguish between vowels and then allow us tospeak (and to sing). What counts forunderstanding of speech, is the relative positionof the formants and not so much their absolutevalue, thus it is possible to sing vowels atdifferent pitch and to remain understandable.
The singing formantIt is an area of resonance of the human voicelocated around 2800/3000 Hz for the men and3000/3200 Hz for the women. This is the regionwhere our ear is the most sensitive, while theinstruments of classical music only produce lowfrequency in this area, allowing the voice goingout over the orchestra.