Points: By and large, language-systems are independent of the medium in which they are manifest.
The natural or primary medium of human language is sound.
Therefore, the study of sound is more important in linguistics than any other language-medium.
But this does not mean that we study all the sounds that humans are capable of producing. The linguist is interested in only those sounds produced by human speech-organs which have a role in language.
***By this time, you are already familiar with the various levels of linguistic analysis - phonetic phonology, morphology, syntax, and semantics. You know that phonology deals with the pattern in of speech sounds in a language?