Final answer:
Low pitch is produced when the vocal folds are relaxed and there's low air pressure, leading to slower vibrations and a lower pitch.
Step-by-step explanation:
Low pitch in human voice is produced when the vocal folds are relaxed and there is low air pressure. This occurs because the vocal folds open and close rhythmically, creating a pressure buildup. As the air travels up and past the relaxed vocal cords, it causes them to vibrate at a slower rate, which results in a lower pitch. Conversely, a voice becomes louder when the airflow from the lungs increases, which increases the amplitude but does not necessarily change the pitch.