That watery, descending riff is one of the most recognisable sounds of the '90s — and it's all about one pedal. Here's Cobain's "Come As You Are" tone.
What makes the tone. The signature is a chorus pedal (a Small Clone-style, set deep) on a clean-ish tone for the riff — that underwater, slightly detuned wobble. The choruses hit with a DS-style distortion, but the chorus stays on throughout. Nirvana often tuned down (to Eb or lower), which thickens it.
The analogue recipe. Chorus pedal always on, deep; clean for the riff and verses, kick in distortion for the choruses. Tune down a half-step for authenticity.
On a Boss GT-100 / GT-1000 / GX-100. A Chorus block on throughout, a DS-style distortion for the choruses, a mid-scooped amp model.
On a Kemper. A clean-to-crunch profile, a deep chorus stomp always on, a DS-style distortion stomped in for the choruses.
Skip the guesswork. The Soulster Tonebook for fans of Nirvana → has the verse/chorus settings ready for Boss GT and Kemper.
Put it on the wall. The "Come As You Are" print → and Seattle poster →.
Comfortably Numb Guitar Tone: Gilmour's Solo Sound
Immigrant Song Guitar Tone: Jimmy Page's Riff