Michael McAuliffe

Synthesizing a vowel continuum

This page will focus on making a continuum between “bit” and “bat”, primarily to illustrate the benefits of frequency anchoring. However, I have many /bVt/ words recorded that can be used as end points for many different continua around the English vowel space:

The temporal structure for creating a continuum follows that in the morphing tutorial.

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You’ll notice that the region corresponding to the vowel in each sound files shows a fair bit of difference, indicative of their different formant structure. Rather than mixing the sound files directly, we’d like to shift the formants around, so we have to align the formant peaks during the vowel as below.

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The continuum created for the “bit” and “bat” endpoints using morphing substrates of bit-bat_A.mat to bit-bat_B is below.

Step File Step File Step File
1 bit-bat001.wav 2 bit-bat002.wav 3 bit-bat003.wav
4 bit-bat004.wav 5 bit-bat005.wav 6 bit-bat006.wav
7 bit-bat007.wav 8 bit-bat008.wav 9 bit-bat009.wav
10 bit-bat010.wav 11 bit-bat011.wav    

Listen specifically to steps 6 and 7 to hear something approximately “bet”-like, as the continuum goes through the /ɛ/ formant region.

In contrast, a continuum created without frequency anchoring sounds using morphing substrates of bit-bat_nofreqeuencyalignment_A.mat to bit-bat_B is below.

Step File Step File Step File
1 bad_bit-bat001.wav 2 bad_bit-bat002.wav 3 bad_bit-bat003.wav
4 bad_bit-bat004.wav 5 bad_bit-bat005.wav 6 bad_bit-bat006.wav
7 bad_bit-bat007.wav 8 bad_bit-bat008.wav 9 bad_bit-bat009.wav
10 bad_bit-bat010.wav 11 bad_bit-bat011.wav    

The boundary between the two is much more abrupt and the synthesis quality is generally not as good.