Crom-Tech had the power to so completely confuse an audience that it didn’t know how to react. When the band opened for Fugazi at Fort Reno in the summer of 1997, Crom-Tech played a 20-minute set full of lightning-fast guitar and drum interplay, screamed over completely incomprehensible vocals. When the band was done, the punk kids that filled the park greeted its members not with cheers or jeers, but only blank stares. Crom-Tech is gone, but the confusion lives on in Orthrelm. There are no vocals, but former Crom-Tech guitarist Mick Barr still blurs the line between all-out improv and prepared interaction. Orthrelm is bound to perplex the innocent bystanders when it plays with Blonde Redhead and Nima Majd at 9:30 p.m. at the Black Cat, 1831 14th St. NW. $10. (202) 667-7960. (Jacob Long)