Two sounds close enough to trade places: the “ch” of chair and the “sh” of shoe. Swap one for the other and a different word comes out — this page is how to keep them apart, in both directions.
Begin with a complete stop — tongue tip against the ridge — then release into the sh friction.
“Sh is a whisper; CH is a whisper with an ENTRANCE! Touch the ridge first, then burst — like flinging open the shutters!”Nunzio, when he hears it
You cannot hear your own swap. That is the whole problem.
Nunzio records you reading a sentence, scores every sound in it on your phone — nothing is uploaded — and tells you which of these two actually came out. Nunzio — Accent Coach is coming to the App Store and Google Play.