The Takacs Quartet, considered one of the world’s best chamber ensembles, has launched its first season without longtime violist Roger Tapping, who left the group this past summer. So how is the Takacs sound faring with new violist Geraldine Walther, late of the San Francisco Symphony? Very well, thank you. “With less than a month’s worth of performances under her belt, Walther — with her warm, honeyed tone, her clarity and confidence — is already a fit with the group, which sounded remarkably, delicately in balance… There was an incredible airiness to Sunday’s performance, with its refined, tremulous atmospherics: It evoked sunlight passing through fog. You could ‘see’ each refracted ray.”