Lab: Measuring Stop-Consonant Voice-Onset Times
The purpose of this lab is to measure voice-onset times for stop consonants, but also to
understand a little bit about how different languages divvy up the phonetic world in different
ways to create their own, language-specific set of phonemic distinctions. The test signals for the
lab are in three .wav files: ‘votsignals.wav’, ‘ba-pha.wav’, and ‘pit-spit.wav’, plus a spectrogram
file: ‘ba-pha.fc’).
Background
VOT (voice-onset time) is the “burst-to-buzz” interval: the interval of time that elapses
between the release of the occlusion (at the lips, alveolar ridge, or the velar/palatal area) and the
onset of periodicity. The onset of periodicity can be seen on a BB gram by the 1st occurrence of
approximately regularly spaced vertical lines corresponding to individual glottal pulses. Stops
for which release and voicing onset are nearly simultaneous, or show a brief lag between release
and voicing onset, are called short lag. Stops that show a significant delay (more than ~20-25 ms
or so, but usually more than ~60 ms) between release and voicing onset are called long lag or
voiceless aspirated. Positive numbers are used for these VOTs; e.g., +80 ms. Stops for which
voicing onset precedes release are called lead or prevoiced, and negative numbers are used for
these VOTs; e.g., -100 ms.
Shown below in some order are signals and BB grams for three words: [pheso] (the
Spanish word peso as it is commonly mispronounced by gringos), [beso] (the Spanish word for
kiss), and [peso] (as close as I can get to the way it might be pronounced by a Spanish speaker).
English has two phonological or phonemic voicing categories: voiced (V+) and
unvoiced/voiceless (V-); i.e., /b d g/ contrast phonemically with /p t k/. However, three phonetic
(not phonemic/phonological) types occur in English. The three phonetic types are the ones
mentioned above: (1) prevoiced/lead, (2) short lag, and (2) long lag/aspirated. How do you get
two phonemic voicing categories out of three phonetic types? Easy. In English, lead and short-lag
stops are allophones or allophonic variants (not variates) of /b d g/. They are in free variation,
which simply means that speakers are free to use either lead or short lag for /b d g/ at their whim.
English is a very permissive language in this way, and listeners are equally permissive – they
treat lead and short-lag stops as equivalent and equally good instances of /b/ (or /d/ or /g/). In
fact, fairly early in native-English speech development, listeners begin to have a difficult time
hearing the difference between lead and short-lag allophones of /b d g/. (Language learning will
do that sort of thing to a person, and this is one of the most important principles in understanding
why learning the sound pattern of a 2nd language can be such a challenge, especially as a person
starts getting up in years.) So, at the more abstract linguistic/phonological/phonemic level,
English distinguishes (or contrasts) lead and short lag as a group with the long-lag category.
Very important note: If you have forgotten or were never quite clear about the all-important
distinction between the terms phonemic and phonetic – i.e., the difference between
phonemic/phonological/linguistic categories on the one hand, and allophonic variants of those
categories on the other hand – it would be a very good idea to dig out a phonetics text and review
these concepts. There’s no way in the world to understand this material on VOT, and especially
its role in 2nd language learning, without understanding those concepts. If you do not have a
phonetics text, see if you can borrow one from a pal (if you have any left) or see me. You can
also find some discussion of these ideas here:
http://homepages.wmich.edu/~hillenbr/204.html
Look for the ‘language’ link (about the 3rd one down), especially the material starting on slide
48. If you review this material and still don’t get it, see me.
Ok, back to the story. Spanish is different. Spanish also has two phonological or
phonemic voicing categories: voiced and unvoiced, but these two voicing categories map onto
phonetic categories in a way that is very different from English. Spanish has only two of the
phonetic types that have been described: lead/prevoiced and short lag. The long-lag/aspirated
phonetic type does not occur at all in Spanish. So how do you get two phonetic categories? Also
easy: Spanish contrasts lead (phonologically voiced) with short lag (phonologically unvoiced).
That’s pretty much it – the lead and short-lag phonetic types that are allophones of +voiced in
English are distinct phonemic categories in Spanish.
The lab exercise
1. votsignals.wav
Start ztool/SpeechTool and open ‘c:\ztool\votsignals.wav’. In some order you will see
three words displayed: [pheso] (the Spanish word peso as it is commonly mispronounced by
gringos), [beso] (the Spanish word for kiss), and [peso] (as it might be pronounced by a Spanish
speaker). Bug the ‘bbgram’ button. Measure VOTs for each of the three words. You already
know how to make time measurements from one of the earlier labs – the one in which you
measured the fundamental period. Line the cursor up with the release burst, note the time (the ‘x’
value in the lower right), then line the cursor up with voicing onset and note the time, then
subtract the two time values to get VOT. If you can see by eye that the two events are nearly
simultaneous, it’s ok to just record a value of zero. That’s it. (If you don’t remember how to
measure time intervals using SpeechTool, take a look at the earlier lab write-up.)
Signal 1
a. VOT: ____________
b. The word is (circle one): [beso] [peso] [pheso]
c. In Spanish, this word is phonologically (circle one): V+ V- neither (does not occur in Spanish)
Signal 2
a. VOT: ____________
b. The word is (circle one): [beso] [peso] [pheso]
c. In Spanish, this word is phonologically (circle one): V+ V- neither (does not occur in Spanish)
Signal 3
a. VOT: ____________
b. The word is (circle one): [beso] [peso] [pheso]
c. In Spanish, this word is phonologically (circle one): V+ V- neither (does not occur in Spanish)
2. ba-pha.wav
If your previous displays are still on the screen, go to ‘Window’ and choose ‘Close all’ (or
just close them one at a time). Open ‘c:\ztool\ba-pha.wav’, then click the BBgram button. (You’ll
probably see a low-frequency buzz running through the entire spectrogram. Ignore it. You
shouldn’t have any trouble differentiating the glottal buzz from the faint buzz that the laptop
manufacturer put there.)
Signal 1
a. VOT: ____________
b. The VOT is (circle one): lead short lag long lag
c. In English, the initial stop is phonologically (circle one): V+ V- neither (not found in English)
Signal 2
a. VOT: ____________
b. The VOT is (circle one): lead short lag long lag
c. In English, the initial stop is phonologically (circle one): V+ V- neither (not found in English)
3. pit-spit.wav (Beware: This is the strange and gnarly pair.)
If your previous displays are still on the screen, close them. Now open ‘c:\ztool\pit-spit.wav’.
Bug the BBGram button.
Signal 1
a. VOT: ____________
b. The VOT is (circle one): lead short lag long lag
c. In English, the initial stop is phonologically (circle one): V+ V- neither (not found in English)
Signal 2
a. VOT: ____________
d. The VOT is (circle one): lead short lag long lag
e. In English, the initial stop is phonologically (circle one): V+ V- neither (does not occur in
English)
Last question: Anything odd going on here? I told you earlier that the English voicing system
contrasts lead and short lag as a group with long lag/aspirated. Here we have two instances of /p/,
so you’d think that they would both be long lag. Are they? If you made the measurements
correctly, and I assume you did, they should both be aspirated. Are they? You should have found
that one of them () is long lag/aspirated, but the other () is short lag/unaspirated.
Now try this slick thing: Use the cursor to highlight just the  part of the sound wave (not
the gram) for the signal on the left, then hit play. It will sound entirely ordinary; i.e., you’ll hear
a normal aspirated /p/. Now try the same thing with the signal on the right – but once again,
highlight only the  part of the sound wave, leaving off the [s] and the closure interval.
Now hit the play button. Does it sound aspirated, or does it sound more like [b] (or maybe the
unaspirated [p] in [peso])? Now use the cursor to select spit, the whole word, including the /s/,
then hit play. It should sound like a /p/ again. Who knew such spooky things could be found in a
nerd fest such as 6010?
So finally, here’s the last question: What’s going on here? If you already know what’s going on
from your previous journeys in the field, just tell me. If not, the answer is not too hard. The
easiest way to figure it out is to take a look at ‘EnglishPhonologicalRulesControllingAspiration.pptx’,
which is a small part of a phonetics lecture on consonant production. Note: There’s a long set up
to this question, but only a sentence or two is needed to answer it.