I've always assumed that [ts] is one of the lesser affricates of English on the cusp of phoneme status given the single minimal pair in pizza/Pisa. I've never studied English phonetics (only general [phonetics] having Czech as the starting point) so when I started preparing some talks on pronunciation for literacy teachers, I was amazed to find out that [tr] and [dr] are considered affricates and [ts] is at best affricate-like. All the samples on the pronouncing dictionaries' CD-ROMs are distinctly pronounced as affricates and yet the Cambridge one even splits the syllables of pizza as /piːt.sə/.
Is there a phonetic reason for this? Am I being misled by my Central European ears? Or is this just a result of convention? I've asked a few non-expert native speakers to contrast pizza/Pisa and Nazi/*nasi and they were all able to do so effortlessly. When asked to reflect on what sound they were pronouncing, one speaker said: 'it's a sort of squished soft sound' - surely a folk definition of an affricate.
The definition of “affricate” has always been a bit tricky when we are discussing English phonetics. (That’s why we set it as a topic for student essays.) Do we define it in purely articulatory terms, interested only in the manner of articulation? Or are we concerned with English-specific phonology? (E.g., do these entities have phonemic status?)
I don’t understand why Dominik adduces Pisa to go with pizza: the consonant(s) in the middle of the latter are voiceless (ˈpiːtsə), while that in the former is voiced (ˈpiːzə). If we’re looking for minimal or near-minimal pairs, there’s more mileage in blitz blɪts vs bliss blɪs, curtsey ˈkɜːtsi vs cursing ˈkɜːsɪŋ, Betsy ˈbetsi vs Bessie ˈbesi. But then who has ever doubted that ts was in contrast to s in English?
Except for a handful of proper names and recent loanwords and the single item curtsey (derived from trisyllabic courtesy), English ts always involves a morpheme boundary between the plosive and the fricative: cat#s, put#s, hint#s, drift#s, list#s, bat#s#man, eight#some. (Please don’t start quibbling about flotsam.) No word begins with ts (ditto: no quibbling about zeitgeist or tsetse). No single-morpheme word ends with ts (except recent loanwords).
In this respect ts is like tθ, just an adventitious consonant sequence straddling a morpheme boundary. On the other hand tʃ occurs readily in initial, medial, and final position in single-morpheme words: chin, kitchen, touch. It even contrasts with the corresponding plosive-fricative sequence: ratchet vs rat shit. The same is true of tr, at least in initial and medial position.
I would even say that to English ears (or brains) ks is probably more of a single unit than ts (because of box, six, exit etc). (Articulatorily, of course, ks is obviously not an affricate, because the articulation is not homorganic.)