Speech output systems, AudioResponse Units (ARU), work with synthetic speech output.
Depending on the concept and use, they can respond to two-tone signals and output speech information via a Voice User Interface (VUI) depending on the keystroke. They may be host-based systems that retrieve their information from a database. Voice output systems can handle many requests with consistent quality at all times.
Voice output systems are used in call centers and IVR systems, Interactive Voice Response (IVR).