Talked about process writing part for certain instruments (4)
I believe the answer is:
reed
'for certain instruments' is the definition.
I can't judge whether this defines the answer.
'talked about process writing part' is the wordplay.
'talked about' shows a homophone (sound like).
'process' becomes 'ray' (raying is a kind of processing).
'writing part' becomes 'ed' (I can't justify this - if you can you should believe this answer much more).
'ray' sounds like 're'.
're'+'ed'='REED'
Can you help me to learn more?
(Other definitions for reed that I've seen before include "Type of musical instrument" , "Bilk had one" , "Marsh plant with tall straight stem" , "Tall water-loving grass" , "Carol" .)