We digitally synthesized versions of the sound of a sharp object scraping across a slate surface (which mimics the sound of fingernails scraping across a blackboard) to determine whether spectral content or amplitude contour contributed to its obnoxious quality. Using magnitude estimation, listeners rated each synthesized sound’s unpleasantness. Contrary to intuition, removal of low, but not of high, frequencies lessened the sound’s unpleasantness. Manipulations of the signal amplitude had no significant impact on listeners’ unpleasantness estimates. Evidently, low-frequency spectral factors contribute primarily to the discomfort associated with this sound.