GF1
The GF1 was co-developed by Advanced Gravis and Forte Technologies (creator of the VFX1 Headgear virtual reality helmet) and produced by Integrated Circuit Systems under the ICS11614 moniker. The chip was actually derived from the Ensoniq OTTO (ES5506) chip, a next-generation version of the music-synthesizer chip found in the Ensoniq ESQ-1 and Mirage, as well as the Apple II.
The GF1 was purely a sample-based synthesis chip with the polyphony of 32 oscillators, so it could mix up to 32 mono PCM samples (or 16 stereo samples) entirely in hardware. The chip had no built-in codec, so the sounds had to be downloaded to onboard RAM before they could be played back. Sound compression algorithms such as IMA ADPCM were not supported, so compressed samples had to be decompressed prior to loading.
The sound-quality of the GF1 was not constant, and depended on the selected level of polyphony. A CD-quality 44.1 kHz sample rate was maintainable up to 14-voice polyphony; the sample rate progressively deteriorated until 19.2 kHz at the maximum 32-voice polyphony. The polyphony level was software programmable, so the programmer could choose the appropriate value to best match the application. Advanced sound effects such as reverb and chorus were not supported in hardware, although software simulation was possible (a basic "echo" effect could be simulated with additional tracks, and some trackers could program effects using additional hardware voices as accumulators).
Read more about this topic: Gravis Ultrasound