Hudson did not use a vocal double. Every high note, harmony line, and raspy belting run heard from Claire Sardina on screen originates from Kate Hudson's actual vocal cords. The production team committed early to an organic audio footprint. While modern Hollywood biopics frequently rely on pitch correction or composite studio tracks patched together from dozens of takes, Brewer sought the chaotic warmth of a smoke-filled room.
Hudson tracked primary vocal passes at legendary production spaces, but key musical sequences were captured directly on camera. Production sound mixers pinned concealed wireless microphones to the actors' wardrobe, allowing Hudson and Jackman to project over live monitor feeds. The result captures genuine human breath, slight pitch breaks born of physical exertion, and spontaneous vocal interplay that pre-recorded lip-sync tracks simply fail to duplicate.
