If you're into the embedded/edu/stem/steam space at all, the micro:bit v2 codebase for audio is being integrated more widely this year, and expanding our audio processing components might be a fun, bounded project if you want something smaller, but reasonably high impact?
See https://github.com/lancaster-university/codal-microbit-v2 for the ecosystem, or https://github.com/lancaster-university/codal-core/tree/mast... for the relevant section of the API.
If you're interested do feel free to suggest stuff via feature suggetions and such on the issue trackers, and PR's welcome :)