Two sounds close enough to trade places: the “a” of apple and the “uh” of cup. Swap one for the other and a different word comes out — this page is how to keep them apart, in both directions.
Push your tongue forward and low, and drop your jaw wider than feels natural.
“Too central, too shy! Bring the tongue forward, drop the jaw, open big — this vowel is front-row seats, bello!”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.