Nada refers to the internal sacred sound, said to arise from the heart.
Nada Yoga may be called the Yoga of Sound, Yoga of the Inner Sound or Yoga of Sacred Sound, and refers to listening to the inner sound.
Mantra Yoga is the repetition of sacred sounds. Repeating a mantra is known as chanting. The practice of chanting mantras may be considered its own branch of yoga (along with Hatha Yoga, Karma Yoga, Bhakti Yoga, etc) or as a practice within other branches.
Kirtan is call-and-response devotional chanting.
The English term “Yoga of Sound” encompasses all forms of “sonic mysticism” including nada and mantra.
Expert Gary Kraftsow uses the accessible term, “vocal sound techniques” to include humming and chanting (both simple syllables and mantras).