Madhyama
From Hindupedia, the Hindu Encyclopedia
Madhyama literally means the middle one.
In the four forms of Vak/sound, Madhyama is the second level, which means subtle. The first is vaikhari, which is the external sound. Madhyama is said to be anahata or the subtle sound, which is heard in the subtle planes and not produced. This is also referred to as the cosmic hiss.