IR is a zero-latency, realtime, high performance signal convolver especially for creating reverb effects. Supports impulse responses with 1, 2 or 4 channels, in any soundfile format supported by libsndfile.

IR files can be for example here: - https://musical-artifacts.com/artifacts?tags=impulse+response - https://musical-artifacts.com/artifacts?tags=ir

For converting 2ch impupuses to 4ch *True stereo* format use 'convert4chan' utility. See man pages.