Windows Media Audio Voice (WMA Voice) is a lossy audio codec that competes with Speex (used in Microsoft's own Xbox Live online service[46]), ACELP, and other codecs. Designed for low-bandwidth, voice playback applications,[47] it employs low-pass and high-pass filtering of sound outside the human speech frequency range to achieve higher compression efficiency than WMA. It can automatically detect sections of an audio track containing both voice and music and use the standard WMA compression algorithm instead.[3] WMA Voice supports up to 22.05 kHz for a single channel (mono) only.[47] Encoding is limited to constant bit rate (CBR) and up to 20 kbit/s.