Associate similar vowels

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The CMUDict is based on regional spoken American English dialects. Certain vowels listed as different would be conflated (or more or less conflated) when sung by a contemporary singer (barring any overpowering accent). Example: DOCK and DOG have the same short "AO" vowel even in my spoken dialect of English, but the CMUDict lists these as different vowels.
This may be a manual (subjective) association process, as there are only 210 possible vowel pairs.
Grading this scale (0 no rhyme, 1 similar, 2 perfect rhyme) may also help with similar vowel association.