diff --git a/papers/doc/4-instrument/README.md b/papers/doc/4-instrument/README.md
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+++ b/papers/doc/4-instrument/README.md
@@ -1,3 +1,14 @@
 # instrument editor
 
-TODO
+Depending on a system used, there are currently 10 different types of an instrument editor:
+
+- [FM synthesis](fm.md) - for use with YM2612, YM2151 and FM block portion of YM2610.
+- [Standard](standard.md) - for use with NES and Sega Master System's PSG sound source and it's derivatives. 
+- [Game Boy](game-boy.md) - for use with Game Boy APU.
+- [PC Engine/TurboGrafx-16](pce.md) - for use with PC Engine's wavetable synthesizer.
+- [AY8930](8930.md) - for use with Microchip AY8930 E-PSG sound source.
+- [Commodore 64](c64.md) - for use with both revison of Commodore 64's SID.
+- [SAA1099](saa.md) - for use with Philips SAA1099 PSG sound source.
+- [TIA](tia.md) - for use with Atari TIA sound controller.
+- [AY-3-8910](ay8910.md) - for use with AY-3-8910 PSG sound source and SSG portion in YM2610.
+- [Amiga/sample](amiga.md) for controlling Amiga and other sample based synthsizers like YM2612's Channel 6 PCM mode, NES channel 5, Sega PCM and PC Engine's sample plyback mode.