The Waterfall’s long, floppy steel bands can be played with lightweight, hard beaters such as ping pong ball mallets. Each band produces a wide range of frequencies, but the lower frequencies are scarcely heard because the bands, being narrow, do not project the lows into the air very effectively. As a result, the sound that reaches our ears is mostly the sizzle frequencies. With bands in this length range, one of those frequencies happens to stand out enough among the many to give the listener some sense of pitch.
A video of this instrument can be found among the demonstrations in this youtube playlist.