i Register
In some senses, subtonic is marked as dated. Watch for register when choosing this word.
adj
Of or pertaining to imperfectly articulated sounds or utterances that are inaudible or barely audible, as characterized by Dr. James Rush (Guide to Pronunciation, 1833).
noun
The note immediately below the upper note of a musical scale.
An imperfectly articulated sound or utterance, as characterized by Dr. James Rush (Guide to Pronunciation, 1833).