multipcm doc

initial revision

doc/7-systems/multipcm.md

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+# Yamaha YMW258-F (MultiPCM)
+
+ a sound chip introduced in 1991 by Yamaha for their first General MIDI-compliant synthesizer, the Yamaha TG100. It also appeared on a number of higher-end consumer keyboards and specialized professional devices. The YMW258-F implements the GEW8 sound synthesis technology, which is PCM sample-based synthesis under Yamaha's "Advanced Wave Modulation" (AWM) umbrella.
+
+Sega used the chip in several arcade games on the Sega System Multi 32, Sega Model 1, and Sega Model 2 arcade boards. The chip as found on these boards is called MultiPCM, and has the Sega internal part number 315-5560. Contrary to popular belief, it is not a custom Sega part and is not based on the earlier SegaPCM chip, but it was named the MultiPCM as a successor to that chip. 
+
+it has a whopping 28 channels of stereo 16-bit PCM and:
+
+- hardware LFO
+- 8bit and 12bit wave format support
+- up to 4MB of wave memory
+- full blown ADSR envelopes
+
+## effects
+
+- `20xx`: **set PCM LFO rate.**
+- `21xx`: **set PCM LFO PM depth..**
+- `22xx`: **set PCM LFO AM depth.**
+
+
+## info
+
+this chip uses the [MultiPCM](../4-instrument/multipcm.md) instrument editor.