EEG already preprocessed

Your EEG is already filtered and referenced (e.g. from your own pipeline or from MNE)? You must stop the pipeline from doing it again.

The idea

Re-filtering an already-filtered signal distorts the low frequencies and biases the covariance; re-referencing twice is a silent error. We switch both steps off.

The arguments

Set l_freq and h_freq to None to disable filtering; eeg_reference=None keeps your existing reference.

result = reconstruct_sources(
    subject="sample",
    output_dir="D:/derivatives",
    t1_path="D:/anat/sample_T1w.nii.gz",
    eeg_file="D:/eeg/sample_clean.fif",   # already preprocessed
    digitization="D:/dig/sample.elc",
    simnibs_bin_dir="C:/Users/me/SimNIBS-4.5/bin",
    l_freq=None, h_freq=None,             # <- no re-filtering
    eeg_reference=None,                   # <- keep the reference
    events="find", event_id={"aud_l": 1},
)

Everything else matches the full tutorial: the evoked response and the sources are computed the same way.