The Apple IIGS's sound is provided by an Ensoniq 5503 DOC wavetable synthesis chip designed by Bob Yannes, creator of the SID synthesizer chip used in the Commodore 64. The ES5503 DOC is the same chip used in Ensoniq Mirage and Ensoniq ESQ-1 professional-grade synthesizers. The chip has 32 oscillators, which allows for up to 32 independent voices, though Apple's firmware pairs them into 15 voices (one oscillator is reserved for system timing) for fuller richer sound, as do most of the standard tools of the operating system (the MIDISynth Tool Set groups four channels per voice, for a limit of seven-voice audio). The IIGS is often referred to as a 15-voice system, because one stereo voice is reserved by the OS at all times for timing and system sounds. Software that does not use the OS, or uses custom-programmed tools (most games and demos do this), can access the chip directly and take advantage of all 32 voices.