Week 1. Acoustic parameters of stress in Welsh

In many languages, the acoustic correlates of stress include raised (higher) pitch, and louder, longer and more peripheral vowel qualities. However, these acoustic correlates are not universal: a fascinating counterexample is given by modern Welsh, as shown by Briony Williams in her PhD thesis and in several articles arising from it (Williams 1982, 1986, 1999). In a perception test, two English and one Welsh listener judged the placement of stress in a list of 20 isolated words read by a native speaker. Their judgements were correlated with the following acoustic parameters:

1. shorter duration of the vowel
12. longer duration of the vowel
2. lower envelope amplitude within the vowel
11. greater envelope amplitude within the vowel
3. f0 change within the vowel of less than 15 Hz (i.e. monotonous)
10. f0 change within the vowel greater than 15 Hz (often very much greater)
4. higher f0 at start of the vowel
9. lower f0 at start of the vowel
5. greater mean amplitude of vowel
8. lower mean amplitude of the vowel
6. greater peak amplitude of vowel
7. lower peak amplitude of the vowel
Williams 1982 figure 1
It can be seen from this figure that Welsh vs. English speakers seem to associate quite opposite acoustic features with stress; in particular, syllables perceived as stressed by Welsh listeners have shorter vowels, lower amplitude within the vowel, monotonous pitch (i.e. no pitch movement) on the stressed vowel. The shorter vowels of stressed syllables may however be associated with a longer following consonant (Williams 1998: 8). Although stressed syllables in Welsh are not associated with pitch movement or peaks, it has also been noted that final syllables in Welsh are often associated with a pitch peak, despite being unstressed (Buczek-Zawiła 2014).

Given the resource constraints of the time at which it was carried out, Williams's study was based upon a rather small amount of recorded material from a few speakers. In order to test the results against a larger amount of data from more speakers, this term's experiment will be an acoustic investigation of some phonetic correlates of Welsh stress in a set of isolated words (citation forms) as spoken by a larger number of speakers. The data will be drawn from the Paldaruo Speech Corpus (http://techiaith.cymru/data/corpora/paldaruo/?lang=en):

Hypotheses that could be tested:

1. Stressed vowels in Welsh are of shorter duration than unstressed vowels
2. Stressed vowels in Welsh are of lower amplitude than unstressed vowels
3. There is <15 Hz change in f0 in stressed vowels
4. Final, unstressed vowels have higher f0 than the (typically, immediately preceding) stressed vowels

Depending on the time available, and the number of students who join the class, we don't need to do all of these, but it is generally advisable in acoustic-phonetic studies to examine a number of different variables because we may get null results with some of them but positive results with others, and we can't tell in advance which parameters will prove most interesting. It is also possible to find no significant differences at all in any of the planned comparisons, which might be a little disappointing but if that happens, it happens. If it did happen, it could be because of insufficient or unsatisfactory data; we can cross that bridge later, if we come to it.

Materials

The Paldaruo corpus was collected in order to train a speech recognition app. It is therefore designed to capture a lot of variation in speech using highly controlled data. It has two parts: randomized isolated words, recorded in sequences of 8 to each .wav file, and short read sentences. We'll use isolated words; the filenames are all of the form *sample*.wav, for example ff3a2aa6-61f2-4d06-a806-7feb99ffdfb2_sample1.wav. Each such sequence of 8 words is available as spoken by hundreds of speakers. A listing of the contents of all the audio files is provided in the corpus as a file called "samples.txt"; I have deleted the sentence transcriptions and highlighted the words with repeated vowels in a document file (see samples.pdf and selection.pdf). The point of selecting those words with the same vowel repeated in two syllables is in order to be able to compare the stressed vs. unstressed version of that vowel as spoken by the same speaker in the same word. There will be all sorts of random variation between speakers and perhaps even between words (different numbers of syllable, coarticulatory contexts etc.); it is also well established that different vowels usually have different durations, amplitudes and "inherent" pitch; for example, open vowels are typically longer and louder than mid vowels, which are in turn longer and louder than close vowels. Therefore, a word such as gyda [ˈgida] might not be a very good basis on which to conclude that stressed vowels have lower amplitude than unstressed vowels, because all other things being equal we expect [i] to have a lower amplitude than [a] anyway. Camfa [kamva], in sample 84, would be a more sensible choice of test-word because one might suppose/expect that the vowels would be pronounced alike, all other things being equal (which they are not ... ), so if they are not pronounced alike it could be because of stress. 

So by comparing the pronunciation of "the same" vowel in two different positions in a spoken word we can control for many unwanted confounding factors in a fairly simple way.

Homework, to prepare for week 3:
 Week 3. Measurements

Here are some zipfiles with a specific portion of the data for you to work on, as discussed in week 1 (not necessarily to do all of it, just divided up between us so that we don't duplicate effort unncessarily). Please let me know when you've downloaded them, so I can take them down from this site.

    Frances.zip    |    Felicia.zip    |    Anastasiia.zip    |    Songjun.zip    |    Toby.zip

In order to test any of the hypotheses, it will be necessary to identify and demarcate (i.e. mark the beginning and end) of the stressed vowels, and for hypothesis 4 perhaps also the final unstressed vowel (except that in disyllabic words it might be simpler to just look for an overall increase in f0 across the whole word).

In the past, one might have made all the measurements of each sound recording one at a time, with considerable manual intervention. But that approach is unnecessarily time-consuming. It is preferable to use scripts to automate the processes of measurement as far as possible. However, since it would be wrong to simply assume that the measurements obtained in that way must be correct, it is important to validate the accuracy of the measurements in some way. The two main methods I advocate are (a) statistical comparison of measurements from the same word(s) as spoken by different speakers; (b) checking a representative sample of the data against manual measurements. The strength of (a) is that it allows one to identify what the general pattern of e.g. pitch or amplitude or timing is for all tokens of a given word, and use that to identify and check the tokens that deviate most of all from the general pattern, on the basis that severe measurement errors will be outliers.

The main parameters we want to measure are (a) vowel durations, (b) "amplitude envelopes" and (c) f0.  For good (most reliable) measurements of vowel durations, it would be best to avoid words with [w], [j], or [l] before or after the vowel. [ɬ] should be fine, because it is voiceless. Nasals can be a bit problematic if one wants to measure formant frequencies, but that is not a main focus of this experiment. Stop consonants and voiceless consonants, on the other hand, are especially good contexts for delimiting vowels.

In order for measurement scripts to work, we need to first label (annotate) the audio with start and end times of each word we are in and each vowel we want to measure. We can do this using Praat TextGrids. In this week's class, we will look at how to create them, what acoustic features we need to pay attention to (segmental criteria) and what standards to use for the labelling.

Our textgrids need to have two tiers: one called "word" and the other called "seg".
On the "word" tier, we mark the start and end of the word(s) of interest, and transcribe the word itself using normal (Welsh) orthography.
On the "seg" tier, we mark the contrasting stressed vs. unstressed vowels, and postvocalic consonants or consonant clusters. A transcription convention is proposed near the top of WelshTextGrids.html
 
We mark the stressed vowel with a "1", the pre-stressed unstressed vowel (if there is one) with a "0" and the post-stressed unstressed vowel with a "2". We only mark those unstressed vowels that are of the same vowel quality as the stressed vowel, though. Thus, in ohonom we transcribe and mark the segment boundaries of o0 h 01 n 03 m, because all three vowels are relevant, but in ychydig /ə'xədig/ we needn't bother to transcribe or mark the segment boundaries of the final vowel, because it has a different quality from the stressed vowel, and therefore we just mark up @0 x @1 d (where @ is used instead of IPA - although IPA symbols can be used in Praat TextGrids, it takes a little more work and some of the later steps in the analysis can't cope with IPA).


Week 5. Preparing to measure the labelled files

We've started to make Praat TextGrids for the words and segments (vowels and following consonants) of interest; the TextGrids are indexed in WelshTextGrids.html

We decided last year that we should probably not work on the word hynny /'həni/ (in sample 20) because the vowels, although spelled alike in Welsh, are phonetically different vowels. They could possibly by analysed as variants of a single phoneme, but it is perhaps better to ignore this case rather than worry about it. For the same reason, we should probably exclude ystyr /'əstir/ (sample 29). We also decided to exclude ysgolion (sample 39), because of the difficulty of segmenting [i] from [o] in the final syllable or syllables.

To help with the next step, I find it useful to convert the TextGrids to .lab files in the xlabel format. These don't have quite such a detailed, hierarchical structure as the TextGrids; their format is simply that each line has three fields (columns): start_tim end_time label
To convert from TextGrids to .lab files, I have written two awk scripts: tgwords2lab and tgseg2lab. In Linux (or Apple OSX) these can be used in a terminal window like this:

$ awk -f tgwords2lab wavs/12tokens/0aebc50d-044e-4f6e-b0f3-70e6c335abe8/0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid > 0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid.words.lab

$ awk -f tgseg2lab wavs/12tokens/0aebc50d-044e-4f6e-b0f3-70e6c335abe8/0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid > 0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid.seg.lab

(Running awk on a Windows PC/laptop takes a bit of work/trouble, but that doesn't matter because once we've made all the TextGrids I can do that process all together.)

Take a look at
0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid.words.lab
0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid.seg.lab

They are just plain text files. Actually, if we just change the filename from .lab to .csv, then we can also look at them in a spreadsheet!
0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid.words.csv
0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample1.TextGrid.seg.csv

Moving on to actually measuring the acoustics. Using the ESPS signal processing package (as in Coleman and Slater 2001: 221-2) in Linux or OSX (more difficult in Windows, but I've already run this process last year anyway), we can pitch track all 2436 selected .wav files at 10 ms intervals with a single shell command such as:

$ for i in */*.wav;
    do sox $i temp.raw;
    btosps -f 16000 -n 1 -t SHORT -c "" temp.raw $i.sd;
    get_f0 -i 0.01 $i.sd $i.f0;
    pplain $i.f0 >$i.f0.txt;
done

The first column of *.f0.txt is an f0 track, second column is probability of voicing (in the range 0 to 1), and the third column is RMS amplitude.

Coleman, J. S. and A. Slater. 2001. Estimation of parameters for the Klatt formant synthesizer. In R. Damper, ed. Data Mining Techniques in Speech Synthesis. Boston, MA: Kluwer. 215-238.

Extracting measurements from the .f0.txt files, according to the .TextGrid or label files

We can convert all of the .TextGrid files to .lab files at once, in Linux:

$ for i in Data/*.TextGrid
    do awk -f tgwords2lab $i >$i.words.lab
    awk -f tgseg2lab $i >$i.seg.lab
done

Then, we can make "to do" lists of segments of interest for measurement. For example, to make a list of all the "o1" segments:

$ awk '{if ($3 == "\"o1\"") print FILENAME, int($1*100), int($2*100), $3}' *.seg.lab > o1list

(The .f0.txt files do not have times associated with each line (they are just 10 ms frames), so we converted from seconds to frame (line) numbers by multiplying the times by 100.)

Using e.g. 01list, we can extract just the relevant lines of the .f0.txt files, and from those lines calculate the average and maximum f0 and rms amplitude. We need to translate each line of e.g. 01list into a code snippet, like this:

0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample39.TextGrid.seg.lab 231 249 "o1"

=>

awk 'BEGIN {sumrms = 0
 f0 = 0
 maxf0 = 0
 maxrms = 0}
 NR == 231 {
 startf0 = $1}
 NR >= 231 && NR <= 249 {
 f0 = f0+$1
 sumrms = sumrms+$3
 if ($1 > maxf0) {maxf0 = $1}
 if ($3 > maxrms) {maxrms = $3}
 }
 END {print FILENAME, "o1", (249-231)/100, f0/(249-231+1), maxf0, maxf0-(f0/(249-231+1)), startf0, sumrms/(249-231+1), sumrms, maxrms}' 0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample39.wav.f0.txt

Here's the translation (sorry, it's rather cryptic). You can alter the input filename (o1list) and the output script name (o1script) to suit.

cat o1list | sed 's/\./\ /g' | awk '{printf "awk ZBEGIN {sumrms = 0 \n f0 = 0 \n maxf0 = 0 \n maxrms = 0} \n NR == %s {\n startf0 = $1} \n NR >= %s && NR <= %s {\n f0 = f0+$1 \n sumrms = sumrms+$3 \n if ($1 > maxf0) {maxf0 = $1} \n if ($3 > maxrms) {maxrms = $3} \n } \n END {print FILENAME, \"o1\", (%s-%s)/100, f0/(%s-%s+1), maxf0, maxf0-(f0/(%s-%s+1)), startf0, sumrms/(%s-%s+1), sumrms, maxrms}Z %s.wav.f0.txt\n",$5,$5,$6,$6,$5,$6,$5,$6,$5,$6,$5,$1}' | sed "s/Z/\'/g" > o1script

Note that a letter Z is used here solely to avoid '...' quotes within '...' quotes. At the end, we translate the Z to \' using sed.

To execute the measurement script, you need to make it executable and then run it:

$ chmod +x o1script
$ ./o1script

o1script prints out
For example:

0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample27.wav.f0.txt o1 0.13 229.554 235.645 6.09121 202.621 3436.79 48115.1 4073.69
0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample28.wav.f0.txt o1 0.14 197.949 250.995 53.0461 0 2292.96 34394.4 3129.76
0aebc50d-044e-4f6e-b0f3-70e6c335abe8_sample39.wav.f0.txt o1 0.18 223.068 236.573 13.5055 211.956 2530.95 48088 4229.13

A .csv file with all this data in one place is available here

 Week 8.

A zipfile of all the data gathered so far is available here