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Is there a difference between an affricate and a plosive+fricative consonant cluster?

According to wikipedia, there is a difference between a plosive+fricative sequence, as in the following example

  • catch it /kæt͡ʃ.ɪt/
  • cat shit /kæt.ʃɪt/

But I honestly can't hear the phonetic difference unless the speaker carefully puts a pause between the morphological boundaries.

The semicircle in the IPA /t͡ʃ/ seems to suggest that /t/ and /ʃ/ are coarticulated, or at least articulated together more than in a typical consonant cluster.

Is there any difference between the affricate /t͡ʃ/ and the cluster /tʃ/? (similarly with /dɮ/, /p̪f/, /ʥ/, and so on) If so, what's the difference, and how could one tell the difference between an affricate and a simple plosive+fricative sequence?

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+1 this is something I've been curious about since the first time I learnt about affricates –  Louis Rhys Sep 16 '11 at 2:55
    
NB your English example only works for speakers who don't pronounce catch /kɛtʃ/. –  Mark Beadles Oct 18 '12 at 16:36

5 Answers 5

up vote 26 down vote accepted

But I honestly can't hear the phonetic difference unless the speaker carefully puts a pause between the morphological boundaries.

You have very good instincts, because this statement is halfway to the answer. An exploration of the topic is best started in a discussion of the differences between the words shoe and chew, which differ only in that the former has a fricative initially and the latter has an affricate.

The period of silence (caused by voiceless stop closures like [t]) that characterizes stops and the "stop" portion of affricates is indistinguishable from regular silence. We only ever "identify" the presence of "stoppiness" as well as the nature of the stoppiness (e.g., bilabial vs. velar) by the influences that the silences have on neighboring segments.

In the case of the postalveolar fricative versus the postalveolar affricate, in the postalveolar affricate, the stop asserts its status by altering the nature (non-technical term used here; I will elaborate) of the following fricative.

Let's compare my totally amateur recordings of shoe versus chew.

Shoe

shoe

Chew

chew

What do you notice?

There are two major differences that linguists have narrowed down as the cues our ears and minds use to differentiate shoe from chew:

  • The fricative is longer in duration than the affricate in general.
  • The loudest point in the fricative occurs much later as a proportion of total fricative length compared to the affricate.

You can even test this out for yourself by doing some basic audio editing in Praat or Audacity.

When our brains hear catch it or cat shit, it is applying these two metrics to figure out which one it heard. Slow ascension to maximum amplitude and relatively long frication noise? Must be shit.

This only really tells part of the story, though. Let's explore the production side a little.

When an oral stop happens, the tongue (or lips) completely constrict the oral pathway. No air (and consequently sound, to an extent) can get in or out. That being said, in the transition process when a non-obstruent like a fricative or an oral sonorant follows a stop in the same syllable (this does not apply all the time, but the story is really complicated), what happens is that in the last few dozen milliseconds air starts coming out from the bottom of the vocal tract. Air pressure behind the stops exceeds air pressure outside the stop. And when the stop is released, air molecules quickly crack from behind the stop to in front of it relatively quickly (on releases of all oral stops, aspirated or not, especially into vowels, you can feel a marked burst of air on your lips or if you put your hand in front of your mouth). This is what we call the stop burst.

Now, many different sorts of things can happen following the stop burst. In the case of the fricatives after stops, the closure relaxes slightly, causing the air to burst, but it remains relatively tight, and air traveling turbulently as it goes through and comes out of that tight corridor is what causes frication noise.

So the story of the affricate (stop into fricative) is that significantly higher than atmospheric pressure builds up behind the closure. When the stop bursts and the tongue goes into constriction position for the fricative, that high pressure of air is released over the early span of the fricative, causing a high amount of noise.

Compare this to what happens when you pronounce a bare fricative. In those cases (e.g., shoe), your tongue goes into fricative position (small constriction), and then your lower vocal tract just starts pushing air through the constriction. The noise does not begin amidst extremely high pressure behind the constriction. That lack of an air pressure gradient causes it to be quieter.

The quicker climb of the affricate case causes a "critical noise/vibration" level to be reached more quickly and the tongue to retreat from its constriction position, hence the shorter duration of fricatives in general (the critical level hypothesis is not that thoroughly explored to my knowledge, but it seems to explain a lot).

So that's the story of fricative versus affricate.

Bring it all the way back to your case, what happens when there's a "syllable break" is important. When there is a syllable break after the stop, the pressure buildup behind the stop closure releases (sometimes audibly, depending on the dialect). Then, the tongue assumes the fricative constriction position during a period of neutral pressure, and then the air starts flowing, and the sound occurs as a regular fricative.

I'm sure this is poorly edited, so I welcome volunteers who would be kind enough to correct me on all the errors I may have made.

@aedia asked in a comment a very interesting question that I'll address as an edit:

perhaps try something like at shoe vs. achoo

That's actually a slightly different case in my mind. The prosodic characteristics of at (being a very weak unit) in at shoe may cause segmentation issues. While I still haven't read anything that's totally convinced me that phonemic affricates exist in English, I suspect that proponents of phonemic affricates might argue that the resegmented form is proof that /tʃ/ the cluster and /tʃ/ the affricate are distinct. Rambling aside, this doesn't appear to prevail in my dialect and the fricative in at shoe emerges like a vanilla fricative:

At shoe

at shoe

Achoo

achoo

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Very well done! –  Daniel δ Sep 15 '11 at 22:48
1  
perhaps try something like at shoe vs. achoo as well (assuming you pronounce them with the same 'a'... I can't think of a more semantically sensible example) to fully cover the plosive+fricative issue in the question? I like the recordings :) –  aedia λ Sep 15 '11 at 23:05
    
What software is that? –  Mechanical snail May 23 '12 at 23:25
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@Mechanicalsnail: praat –  Steven Xu May 24 '12 at 14:16

The main difference is phonological, not phonetic. In many languages including English, /t͡ʃ/ is a separate phoneme from /t/ and /ʃ/, although the phonetic pronunciation could be identical in some dialects. That is, most speakers would perceive the phoneme /t͡ʃ/ as sounding different from /t/ and /ʃ/, even if the waveforms are identical.

In many circumstances, however, the waveforms may not be identical and you may be able to tell the difference between an affricate and a plosive+fricative sequence due to other phonological processes in a particular language. For example, many American English speakers would pronounce cat shit (phonemes: /kæt.ʃɪt/) with unreleased final t's [kʰæt̚.ʃɪt̚] or even final glottal stops [kʰæʔ.ʃɪʔ].

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When you say they are separate phonemes in English, what is it that makes them so? Often we perceive the phonemes of our own language differently to how linguists analyse them - or am I wrong in thinking that? Also as I recall we do not naturally perceive phonemes at all but syllables. We have to learn to perceive phonemes and some people find it very difficult to do so. –  hippietrail Sep 16 '11 at 15:35

The Wikipedia article in question makes some points that can help in telling the difference. Look at the narrow transcription:

  • cat shit → [ kʰæʔʃɪt̚ ]
  • catch it → [ kʰæt͡ʃɪt̚ ]

Here /t/ debuccalizes to a glottal stop before /ʃ/ in many dialects

If you don't notice this in your dialect, I suggest trying some of the examples of places /t/ debuccalizes:

get ready ['ɡɛʔ'ɹɛɾi]
cotton ['kɑʔn̩]

(these strike me as particularly obvious examples where it would be unlikely to articulate the /t/ in American English).

Wikipedia also says

In the stop-fricative sequence, the stop has a release burst before the fricative starts; but in the affricate, the fricative element is the release. [in reference to one of the non-English examples]

The acoustic difference between affricates and stop+fricative sequences is rate of amplitude increase of the frication noise, which is known as the rise time. Affricates have a short rise time to the peak frication amplitude while sequences of stop and fricative have relatively longer rise time (Howell & Rosen 1983, Johnson 2003, Mitani et al. 2006).

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Like @Krubo, I always thought of the distinction between an affricate and a stop-affricate sequence as being primarily defined in phonological terms. (But of course this does not preclude phonetic differences.) But also, like @hippietrail, I was under the impression that native speakers generally don't have intuitions regarding whether sounds are separate phonemes or not.

So I always thought that in order to tell whether a stop+fricative corresponds to a single affricate phoneme, or a sequence of phonemes, one has to examine its (or their) phonological behaviour with respect to previously motivated phonological restrictions.

For example, if a language disallows syllable margins of a certain complexity, and the only way you could analyze an example with the relevant stop-fricative according to your previously-motivated syllable template is in a way that treats the stop-fricative as a single phoneme (or a sequence of phonemes), then you have an argument that the stop-fricative is a single phoneme (or seq. of phonemes).

Or if you know that vowels are always, say, lax before a complex coda, but not before a simplex coda, and vowels are not lax before the stop-fricative, then you have an argument that the stop-fricative is a single phoneme.

Or a metathesis process, or gemination process, might treat the stop-fricative as a single unit, etc.

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Your ability to hear the difference can be dependent on the language you speak. Most languages don't make a strong distinction between affricate and a plosive+fricative and it may be difficult for their speakers to hear the difference. Some languages have a very clear distinction however.

For example compare these two words in Polish

  • czy - "if, whether" (pronounced [t͡ʂɨ], a bit like chee)
  • trzy - "three" (formal transcription is [tʐɨ], but often pronounced [tʂɨ], a bit like tshee)

This Wikipedia article contains multimedia files for "czysta" vs. "trzysta".

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What's the phonetic difference between those? –  Mechanical snail Sep 13 '12 at 5:37
    
@Mechanicalsnail [t͡ʂ] is a single sound, but [tʂ] are formally two. IPA indicates the difference with ligature. –  bytebuster Sep 27 '12 at 15:35
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@bytebuster Explaining that "[t͡ʂ] is a single sound, but [tʂ] are formally two" is begging the question; the OP is asking why this situation is exists. The phonetic symbols are discrete, but the articulation and auditory phonetics of the two sounds are extremely close. –  Mark Beadles Oct 18 '12 at 16:40
    
@MarkBeadles The OP has not asked why it happens, but it must be just a coincidence; likewise various anecdotes "experts exchange" and so on. –  bytebuster Oct 18 '12 at 16:55

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