The author of NAudio, a 25-year-old open-source .NET audio library, shares his experience using Claude Code (via Anthropic's free OSS program) to modernize the codebase for a major version 3 release. Key modernization efforts include adopting Span<T>, migrating COM interop to GeneratedComInterface for IL trimming and Native AOT support, SIMD/vectorization optimizations, improved memory management for WASAPI wrappers, and restructuring the project layout. Claude Code was used as a pair programmer for API design discussions, large-scale refactoring across hundreds of files, test scaffolding, documentation auditing, and tackling previously out-of-scope features like a spectrum analyzer and synthesizer. The author is candid about limitations: AI can introduce subtle bugs (especially in COM interop causing access violations), ignore instructions, or drop code during refactoring. Manual code review remains essential. Despite a claimed 10x speed-up, expanded scope and debugging time mean total hours invested have actually increased. An alpha release on the naudio3dev GitHub branch is planned soon.
