It's a stripped down LokSound Select decoder that ESU created at ScaleTrain's request (I think, at least so far only ScaleTrains is using them). Only the ScaleTrains non-Rivet Counter versions are supposed to have them. They are like the OEM SoundTraxx Tsunamis that are in Bachmann locos. If I remember correctly, there was a snafu in advertising where the "Operators" (?) versions were listed as having the LokSound V4 like the Rivet Counter version but it was an error.