Spectrographic Measurements of F1 and F2 for Vowels and Vowel Synthesis
The purpose of this lab is to teach you how to measure formants from computer-generated spectrograms. You will measure formant frequencies of isolated vowels from your own vowels in Dr. Speech. You will need to use the micropohone headsets in the box up front in the S164 cluster. Make sure you return the headsets for other students.
This lab builds on Homework #12. Spectrograms were produced on paper by mechanical systems until about 20 years ago. Since then, computer displays of spectrograms have improved to the point that they are now the standard. The quality of computer generated spectrograms is still poorer than the older spectrographs that were built specifically to produce fine resolution pictures.
Refer to the vowel spectrograms on Homework #12B. Frequency is on the ordinate and increases from the bottom to the top. Markers are shown as crosses at 500 Hz intervals. Frequencies from 0-4000 Hz are marked on the spectrograms. The lowest bar is F1, the second bar is F2, etc. To measure the formant frequencies, we draw a line midway through each bar and estimate the frequency relative to the nearest 100 Hz.. Choose a frequency value during the more steady-state part of the formants, or about 1/3 of the way through the vowel when there is formant movement, e.g. /e/ and /o/. vertical striations represent cycles of vocal fold vibration.
We will use Dr. Speech to make spectrograms that look pretty good and automatically offer the formant frequencies (refer to the Dr. Speech Instructions on Assignment Details). Make spectrograms of your own vowels of English, /i/, /I/, /e/, /eh/, /ae/, /a/, /uh/, /aw/, /o/, /U/, /u/. You are to measure F0, F1, F2 and F3 and put them in a table for each vowel like Table 7.1 in the Speech Chain, except you should include the fundamental frequency, F0.
Speak the vowels as steady-state vowels about 1 second long. Use the the green box to mark off a vowel to make clearer spectrograms, if necessary. Measure F0 first, and then use the 'SG' button with the red, blue & green lines for the spectrogram. You can measure the formants by activating the 'Read x,y' data cursor function, either by clicking once in the spectrogram or under the Analysis menu. Measure F1, F2, and F3 for each vowel in the steady-state portion for your table. Construct an F1 X F2 plot as discussed in class and similar to the male-child plot shown here.. Turn in your table and your F1 X F2 plot.
Now go to http://www.asel.udel.edu/speech/tutorials/synthesis/vowels.html which is an online vowel synthesis tool. Using your table of measured vowel formants and F0, synthesize 6 vowels, /i/, /I/, /e/, /eh/, /ae/, /a/. Use the "GAI" gain as 78, as suggested. If you type in a frequency greater than 3100 Hz for F3, you will get an error - just set to 3100 Hz to avoid the error. Adjust your 3 formants so they sound somewhat like your vowels. Store the six vowels you synthesize following the instructions on the web page. Upload all five vowels to your DropBox in Oncourse that is already available to you (instructions on our Assignment page).
Answer the following questions:
1. Explain what a spectrogram is in your own words. Include a description of formants.
2. Explain what a formant synthesizer is (Speech Chain, Chap. 8, p162-166 is a good reference).
3. Listen to the vowels that you synthesized. Comment on whether they sounded like you and had good quality, or not, and if not, what sounded poor to you.
4. Your F1/F2 plot of vowels so that the vowels should be arranged in a pattern similar to the pattern in the phonetic vowel quadrilateral. Which formant corresponds to vowel height? What values of this formant's frequency are found in high vowels? Low vowels?
5. From your F1/F2 plot of vowels, which formant corresponds to vowel backness? What values of this formant's frequency are found in front vowels? Back vowels?
For your lab report, follow the Guidelines for a Lab Report on our web page. Under methods, describe techniques you learned here for measuring spectrograms and synthesizing vowels. In the results, provide a table of the frequencies for F1 and F2 that you have measured and the F1 X F2 plot . Include the answers to the five quesitons under results. The length of the report should be about 2-3 pages (plus figures).