Singing is like every other sport. You HAVE to warmup if you want to achieve peak performance. Humming is a terrific exercise to warm up your voice before you start to sing. Say the word, “hmmmmmmm?” Now move your pitch up. As you do that, you will feel a buzzing sensation inside your nose. Now move your pitch down. You should feel that same sensation down your neck and into your stomach. Now hum do re mi. Then mi re do. Repeat this 5 times.