PortAudio

Every platform has its own way of talking to the sound card, and Windows has several at once. PortAudio grew out of discussions on the music-dsp mailing list in the late 1990s, with Ross Bencina and Phil Burk doing most of the driving, and puts a common layer over all of them: ASIO, WASAPI, Core Audio, ALSA, JACK and a few more. A program opens a stream, picks a sample rate and buffer size, and gets either a callback or a blocking read/write interface.

Audacity is the best-known user, but the library also sits under Python's sounddevice and a long tail of research and hobby projects. Thin, old and boring in the best sense — if you need something bigger, you reach for JUCE.