The YM2413, also called OPLL, is a very low budget sound chip manufactured by Yamaha Corporation and based on their YM3812 (OPL2). To make the chip cheaper to make, many of the internal registers were removed. The result of this is that the YM2413 can only play one user defined instrument at same the time. The other channels have to play one of the 15 built-in instruments. There were other cost cutting modifications such as having only 2 waveforms, and not having the channels added together - instead, the chip's DAC plays each channel one after the other, and the output of this is usually passed through an ( analog) filter. The YM2413 was used as a sound expansion on the following platforms: the MSX, the Master System, and a Japanese NES game called Lagrange Point.
