A witch flew into the Wigmore Hall on Tuesday. Raising her violin bow like a broomstick, and clad in wind-torn silks, Iva Bittová, the Czech violinist and singer extraordinaire, made her entry up and along the aisle, gurgling and gargling musical spells from deep within her throat.

Bittová’s “Improvisation”, as it was billed, lasted for 10 minutes. And the audience, for whom a couple of Janácek string quartets played by Bittová’s compatriots the Skampas is usually quite enough excitement for one evening, was entirely bewitched. As the fluttering, rasping and groaning rose higher and higher, the bow was lifted on to the strings. Teeth clicking collided with double-stopping, and coloratura met high harmonics so that, increasingly, it became impossible to tell whether it was larynx or horsehair that was vibrating.

Janácek, who notated the cries of hens and geese with glee, would have loved it. And his own music was to follow, magically transformed in an arrangement by Bittová and the Skampa Quartet, of his Moravian Folk Poetry in Songs.

Every quartet, it seems, must now have its tame — or not so tame — folk singer. Just as the Takacs are teaming up with Márta Sebéstyen, so the Skampa tuned their fiddles to the raw, childlike and ever metamorphosing voice of Bittová. They all raised their own voices as well as their bows to celebrate the Gnats’ Wedding; they conjured Love as fickle as a swift river; they turned and twirled with Bittová’s midnight-blue skirts as they seduced the Bailiff’s Daughter.

Before the interval, the Skampas’ Janácek quartets (the Kreutzer Sonata and Intimate Letters) had emphasised their folk roots, focusing on the physical muscle rather than the metaphysical mystery of what is, for these musicians, all too familiar territory. And, at the end, a graphic soundscape for voice and quartet called Rain; and two movements from Bittová’s first composition for string quartet: a vocal/visual fusion that very nearly had them dancing in the aisles.