We don't have synonyms for spectralist yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are specialist and spectrality.
(adj) :
Of, pertaining to, or participating in spectralism, a school of musical composition strongly influenced by the spectrographic analysis of sound
(adj) :
Of, pertaining to, or participating in spectralism, a school of musical composition strongly influenced by the spectrographic analysis of sound