In my experience, if I cannot hear myself it means I AM playing in tune! As soon as I have a spell of poor intonation, I hear it and correct it (maybe). If I need a quick check anyway I point the horn at my stand - that usually gives it a boost back. Usually, though, I rely on my knowledge of the individual instrumental idiosyncrasies and I find that generally, if I do not think about it, my ear-brain-embouchure link takes care of the details for me. If you've ever tried to play or sing out of tune, you know how hard you have to work to make it 'bad'. That's the 'survival instinct' I refer to; the natural tendency we have to make it right. At some point, one learns to rely on and trust that.