Actionable information : 70% of American English sounds have lengthened duration; the others are quick. In contrast, many languages including Indian English produce predominantly quick speech sounds.  Information alert:  Spanish and Japanese are reported to be the most quickly spoken languages in the world because all their consonants and vowels are quick.  For clear understandable American English speech sounds, the slow consonant sounds are as much as double slow compared to the quick consonants, i.e., slow v, f, th, s, z, L, r, w  etc. compared to quick p, b, t, d,  k, g, ch, j. PS Positioning of articulators– including especially tongue, and lips, teeth, jaw, is critical and can be different for accurate English speech sounds.