After that is your next project to fix that sticky "i" key on your keyboard?
I would find out what causes intelligibility, and go from there.
The transmissions are likely digital, so the CODEC is going to have a lot to do with reproducibility of the natural sounds.
MIC quality, and proper MIC selection for the job.
Background noise rejection, like that used on cell phones.
compression, transmission
Then the speaker used to playback the audio should be matched to the MIC specs as close as possible. That way, you know the speaker is able reproduce what the MIC "hears".
Quality materials, and codec are probably the biggies.
AudioGuru, you think a 741 opamp will help?
Just kidding, but you are the sound man.
Also, Mr. RB has made a codec which I believe is designed to reproduce the human voice over smaller bandwidth (1 bit). You may want to look into that.
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