Demi Lovato Vocal Range

Vocal Type: Mezzo-Soprano
Vocal Range: 3 Octaves Eb3-Eb6
Vocal Strengths: Wide Range in Chest Voice (up to A5 live) and Strong Vocal Endurance. An overall top-echelon belter.Uncanny ability to emote with her vocal delivery, and possesses a unique, slightly raspy tone when singing mid-range. Incredibly versatile in terms of what genres her voices fits with. Can go from Rock to Balladry to Broadway to Rand B in a flick of a switch. This used to be a con, but is now a strength: her melismatic control. If you listen to old recordings of her and compare them to 2011 live performances, you can't imagine how much she's improved in that department. What used to sound incredibly messy and uncontrolled is now clean, precise and musical. Turned a con to a strength through experience.

Vocal Weaknesses: She needs serious work with her head voice and falsetto, probably because she never used it very much in her past work. She really doesn't have the best control in that technique, and could stand to get vocal training. Her low register could also use some work, though it's WAY better now than it used to be. Back then this part of her register was so foggy and unsupported at times that it would sound like she was speaking rather than singing. It could still use more work, but she's getting there.
Her vocal tone, though unique, certainly isn't for everybody. I'm sure that there are some people that hate how raspy her voice can be at mid-range. I think it adds character and emotion, but it may be viewed as a negative by some.

Selena Gomez Vocal Range

Vocal Type: Mezzo-Soprano
Vocal Range:  2 Octaves, 6 notes and 4 semitones D3-C6
Whistle Register: No
Vocal Pluses: Sold, clear tone to the low/mid range and chest voice, with a warm, soft head voice.
Vocal Negatives: Voice doesn't appear to have much dexterity, and the lack of vibrato on the chest notes make them sound a little harsh to the ear.

Whitney Houston Vocal Range

Vocal Type Mezzo Soprano
Vocal Range: 3.2 Octaves. A2- C6 (approx)
Whistle Register: No
Longest Note: 9 seconds - 'I will always love you'
Vocal Pluses: The timbre of Whitney Houston's voice is her crowning glory: thick, luscious and velvety. Her midrange is where the voice finds its strength, and she is famed for her powerful, dark and emotive belting at the top part of this range. The higher chest notes, past a C5, lose power and weight as they ascend higher and are mixed with the head voice, but they still retain a notable, and identifiable, character. The head voice, on its own, is thick, warm, and slightly smoky with a resonance that mirrors that of her midrange belting voice. Whitney is able to switch to this part of her voice with apparent ease.

Whitney Houston is famed for having brought melisma/vocal runs to the masses, and as such, it is no surprise that her voice is able to execute incredibly fast, and complex runs with pinpoint accuracy. She also has the stamina to hold notes- see I Will always love you- for lengths of time without wavering in pitch. Notes can also be coloured with the use of her impressive vibrato, which she can modify the speed of to dramatic effect by quivering her lip. Her trademark vibrato, along with the midrange belt and thick head voice, is one of the iconic aspects of her remarkable voice.

Vocal Negatives: Whitney Houston's voice can become shrill in the upper range, especially when attempting to belt the higher fifth octave notes.

Shakira Vocal Range

Vocal Type: Coloratura contralto
Vocal Range: 3 Octaves 1 note E3-D6
Whistle Register:No
Vocal Pluses: Unique and versatile vocal styling that incorporates a yodelling like technique as well Arabic influences. The voice has a heaviness pervading throughout, though surprisingly it seems to be most prevalent in the midrange and low belting range.  This weight can be removed, revealing a contrasting crisper, lighter and more youthful sounding timbre. Her head voice is strong and bright, becoming more piercing the higher it becomes, but isn't often used. She is capable of complex meslisma, usually built on a middle eastern musical scale, as well as able to hold sustained notes with or without vibrato. The vibrato itself, is quick but controlled.
Vocal Negatives: Her voice sounds as if it's artificially gaining its weight via her larynx being forced down, as her talking voice is light. Her vocal styling and intonation can also make comprehending her lyrics hard to do.