For my MA thesis, among other things, I am coding the realisations of /t/ in English, by L2 speakers, as: 1) "normal" t, or 2) flapped, d-like t, 3) missing t, and 4) glottalised t.
While I have tried to code it by ear, I would prefer a more secure method. I have been looking at the wave forms of the sounds in praat (http://www.fon.hum.uva.nl/praat/), but still find it difficult. There are times when a /t/ sounds like a [d] to me, but looks like a [t] in praat. I think the reason that it sounds like a [d] may be due to a reduced VOT (voice onset time). Also, there are times when the t looks like it is invisible or glottalised, but on closer examination, there does seem to be a tiny t-wave form. I also find it difficult to tell objectively whether a t is simply missing or whether it is glottalised.
Do any of you have any tips or resources for this?