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As a Spanish learner who didn't grow up listening to the tiny difference between similar groups like ta te ti to tu y da de di do du,pa pe pi po pu and ba be bi bo bu. It is not easy for me to hear and to speak the differences, but after training I may be able to speak them correctly. However, I need to think carefully before speaking it and I find that speaking the 'd' pairs is a bit harder and need more tongue movement. So my question is: how do people speak these words correctly when they speak Spanish fast, because there is no time to do the tongue movement with the right part of the mouth? Is it still important to speak these similar groups correctly when speaking Spanish fast, or is it hard to speak them accurately when they speak fast. I am not able to hear the differences between them at all when they speak fast!!