Austin Shijo wanted a Linux version of a Windows audio effect that pushed music out of the head and made it feel less pressed against the ears. Writing on epestr.com, he describes first trying to rebuild the effect by hand with PipeWire, HRTF databases and an LLM as a sounding board. The MIT KEMAR set was recorded in an anechoic chamber and sounded wrong to him. SADIE II, which includes room responses, came closer, but the project stalled.

The second attempt skipped the algorithm entirely and measured the filter instead. He only had access to the program on a friend’s laptop, so he built a single test file, played it through the effect once and recorded the output.

The file packed in impulses at three amplitudes across both channels, a logarithmic sine sweep, steady tones, a multitone, repeated sections and a noise segment, plus clicks at the start for alignment. The checks confirmed the main surround mode was linear and time invariant, so four impulse responses captured it.…