Poor articulation. Some singers tend to have poor articulation due to the tension on their lips, palate, jaws, and so on. Sometimes, the speaking habit of the singer gets translated into their singing, which can affect the overall quality of their voice.
Limited range in pitch. All types of singing voices have their optimal pitch but due to the lack of coordination of the vocal chords and breath support, the transition in register is not as smooth as everyone hopes. A break will be easily noticed once the singer changes his or her pitch.
Aspirate or hard glottal attack. There are some singers that aspirate before phonation where excessive air is pushed out causing a breathy tone in their singing. The same thing occurs in hard glottal.