There are several different things that are modulated in forming phonetic sounds. The [International Phonetic Alphabet](https://en.wikipedia.org/wiki/International_Phonetic_Alphabet#:~:text=The%20International%20Phonetic%20Alphabet%20(IPA,speech%20sounds%20in%20written%20form.) categorizes all possible combinations of these to form a script that can accurately describe the pronunciation of words in any language. Notably there are some combinations that are impossible, and there are some possible combinations that are not known to exist in any language.
It would be very difficult to create an instrument that could be manipulated to modulate enough variables to recreate speech. However a talkbox is a really neat little device that plays the sound of an instrument into your mouth so that you can use your own mouth to modulate the sound and make words that sound like a guitar or keyboard or whatever.
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