RE-EDIT: Wait im confused how come he's switchin between loud and soft?
It's a style of recitation. There is nothing wrong with reciting like that.
This explanation by SoundVision might help:
The term tarteel is derived from the Arabic root rtl
meaning the recite slowly. Tarteel is measured recitation of the Quran in rhythmic tones. It follows all the rules of tajweed giving every letter its correct articulation, observing all qualities of letters. Tarteel is the method most popular reciters of the Quran use today.
Example of tarteel is the recitations I linked to on Islamway.
Tajweed is from Arabic root jwd
. Literally it means beautification or making things excellent. Muslims use this term for the rules of reciting Quran in precise accordance with the established rules of pronunciation and intonations, such as tafkheem, velarization, Ghunnah, chanting, and Iqlaab, transposition. This discipline is taught in Islamic schools as ilmut tajweed (art of tajweed).
Example of Tajweed is recitations on kitabullah.com
The difference between Tarteel and Tajweed:
Tarteel and Tajweed, both, follow the rules of ilmut tajweed. Tarteel, however, is relatively faster paced then Tajweed. Unlike the word Tajweed, the term Tarteel is used by Allah in the Quran: And recite the Quran with tarteel in slow, measured rhythmic tone (73:4).