This decoder is for converting Märklin/Trix H0 locomotives with built-in high-efficiency motors or other DC motors. The märklin SoundDecoder3 has a 21-pin interface connector and an accompanying interface connector circuit board for converting analog and digital locomotives.
The märklin SoundDecoder3 supports the digital formats mfx, MM1, MM2, and DCC.
The decoder has preset sound for an electric locomotive. Additional how-to videos can be found at http://www.youtube.com/c/maerklin