Summarize the text and tell me what is Sonova?

Context: Sonova Holding AG is an internationally active Swiss group of companies headquartered in Stäfa that specializes in hearing care. The Sonova group operates through its core business brands Phonak, Unitron, Hansaton, Advanced Bionics, AudioNova and Sennheiser. It is one of the largest providers in the sector worldwide. The group and its brands hold 24% of the global hearing aid market in sales. As of 11 September 2022, Sonova is a component of the Swiss Market Index.

Answer: Sonova Holding AG is a Swiss group of companies headquartered in Staefa that specializes in hearing care.