I love Tiffany, but she just doesn't know how to sing. Everyone always defends her and says she's sick, but no, she just sings badly! She doesn't use good technique, and that makes her throat hurt which eventually makes her sound like she does in these performances. This is why she had nodes twice already. Taeyeon and Seohyun both sing as much as she does with SNSD and TTS promotions, and sure sometimes they sound tired but they can still sing well long into promotions. You can start hearing Tiffany's singing affecting her voice after just one week of promotions, making her sound sick and hoarse. She seriously needs better training, her voice is lovely at the beginning of promotions before she ruins it with her bad techniques.