This is a Shepperd Tone generator and its default patch. This provide the classic endless rising or falling tone.
Shepperd Tone Generator: The endless rising / falling tone. Bandwidth set the interval between each sine and also the interval between the sweep start & stop frequencies. The speed simply sets the sweep rate. At fastest rate or at low bandwidth, the "endless" tone fx dissapear and you start to distinguish AM/FM kind of sounds. by SoundMod