It’s an old truism of acoustic phonetics that you can’t hear the hold stage of a voiceless plosive (as such).
What you get in the middle of a word such as happy ˈhæpi or lucky ˈlʌki is a short period of silence, as the airstream is for a moment prevented from moving through the vocal tract and out of the body. No air movement means no sound.
How, then, can we identify the place of articulation? How do we know that in the first word we have a bilabial p but in the second a velar k?
We know because of the formant transitions created as the organs of speech move into place for the complete closure (the ‘approach’ phase) and then again as they separate (the ‘release’ phase). You identify the p in happy through its effect on the end of the æ and on the beginning of the i. You identify the k in lucky by what you hear in the course of the ʌ and the i.
In the case of a fully voiced plosive, all you can hear during the hold phase is voicing. Again, you identify the place of articulation through the information contained in the formant transitions before and after, i.e. in the approach and the release. That’s how you know that abbey has a b, ladder a d, and lagging a g.
Let’s get back to the plosive clusters we were discussing on Friday apropos of Gdynia. In an English word such as acting ˈæktɪŋ we normally have the same ‘masking’ phenomenon we observed for the voiced plosives in hugged and Ogden.
In the English kt or gd the plosives typically overlap, in that we make the approach for the second plosive before releasing the first. The sequence of events is velar approach – velar hold – alveolar approach (inaudible, because the velar hold is maintained) – double hold (velar and alveolar) – velar release (inaudible, because the alveolar hold is maintained) – alveolar hold – alveolar release. The only audible phases are the velar approach and the alveolar release. In these the formant transitions supply the clues to the places of articulation.
To identify the place of a plosive it is sufficient to hear either the approach or the release. You do not need both. That is how we can tell that the word is ˈæktɪŋ rather than, say, ˈæptɪŋ or ˈætkɪŋ or ˈættɪŋ.
My impression from my first visit to Poland was, then, that for Polish gd- the two plosives did not overlap in the English way. Rather, the sequence of events was straightforwardly velar approach – velar hold – velar release – dental approach – dental hold – dental release. Rather than taking place during the velar hold, the dental approach was delayed until after the velar release. The tiny transitional nonsyllabic schwa between the plosives is created in the tiny interval of time between the two articulatory gestures, velar and dental.
We can leave the native speakers of Polish to debate whether this non-overlapping is usual, as I supposed, or only found in careful or overenunciated pronunciation, as some seem to claim. My impression is that if we compare English actor with Polish aktor it is typical for the English plosives to overlap but for the Polish ones not to. Similarly with the name Magda.
In strongly Japanese-accented English, on the other hand, a word such as actor tends to have a greater interval between the release of the k and the approach of the t. This space might be identified as a Japanese voiceless ɯ̥ (thus “ アクター”). Typically, it seems to be much longer than the momentary mini-voiceless-schwa of the Polish kt. It reflects the Japanese mora-based timing in which equal time is allotted to each of a, k(u), ta, a.