It seems there might be a bit of confusion in your question, as "embouchure" specifically refers to the way a musician shapes their mouth and uses their facial muscles to produce sound on wind instruments, particularly brass and woodwinds. It involves the positioning of the lips, tongue, and facial muscles to create a proper seal and direct airflow into the instrument.
On the other hand, string and keyboard instruments, such as violins or pianos, do not utilize embouchure in the same way. Instead, sound production on these instruments relies on techniques related to bowing, plucking, or pressing keys.
If you're looking for information about sound production techniques specific to string or keyboard instruments, please let me know!