Instead of choosing one of the classic EQs that have been modeled one or more times already, Soundtoys searched deep into their gear collection and dusted off a little-known, but much-loved (by those in the know) German equalizer module, the W295b. With Sie-Q, Soundtoys engineers meticulously modeled the musical curves of the W295b, and the harmonic distortion of its discrete transistor circuitry.
Like the more well-known Neve and API modules, the original W295b was used in the Siemens-Sitral line of analog mixing consoles. Those consoles, though built like tanks, were known for their smooth EQ curves and sonically appealing coloration. The W295b in particular is revered for the space and air created by the high frequency band.