First post, by Great Hierophant
- Rank
- l33t
The Game Blaster's sound chip has been described as four IBM PCjr./Tandy 1000 sound chips. This statement is inaccurate in two respects. First, the Creative Music System/Game Blaster uses two identical sound generator chips, relabeled Phillips SAA 1099s. One chip is used in the MGT Sam Coupe. The Tandy 1000 and the IBM PCjr.s have one Texas Instrements SN74689/74696. This chip was used in the Colecovision, the Coleco Adam, the Acorn BBC Micro, the SG-1000/3000, and in integrated form in the Sega Master System/Mark III, Sega Game Gear and Sega Genesis/Mega Drive consoles.
The Game Blaster and early Sound Blasters have two sockets for their relabeled SAA 1099 chips (which may or may not be pin compatible with the standard Phillips chips.) Six tone generators plus two noise generators, 11-bit frequency control, 4-bit volume control, two envelope generators per chip. Each three tone generators is paired with a noise generator, and each channel can output noise, tone or both. Simple AY-3-8910 like envelopes can be applied to two of the tone generators. Each channel can have its volume independently selected for the left and right audio outputs. Noise frequency is predefined or user selectable (which robs a tone frequency generator for this purpose.) Each individual tone and noise generator can be turned on or off as can all of them.
The SN74689/74696 chip is a far simpler chip. Three tone generators plus a noise generator, 10-bit frequency control, 4-bit volume control, mono The noise generator is entirely separate from the tone generators, and the frequency can be predefined or user selectable (which uses a tone frequency generator but allows it to drive the tone generator as well.) Noise can be set to periodic or white noise. The Game Gear, which allows for stereo functionality, simply directs channels to right and or left audio output.