From the Lenz website
-The Gold Series decoders deliver exceptional motor control with a 23kHz silent Back EMF motor drive and revolutionize model railroad control with RailCom, USP, Asymmetrical DCC and SUSI sound interface. New Gold Maxi now available.
The USP is a great feature
USP is an exciting new feature in DCC. In the past decoders have uses contact to the rails to be able to detect and act upon the DCC signal. Capacitors are sometimes added to decoders to provide them more of an ability to operate over dirty track sections. The problem with all these approaches is that while on the dirty track the DCC signal is lost and adding capacitors can have adverse effects such as problems in programming or excessive loads on startup.
To solve the age old problem of poor operations on dirty track, Lenz GmbH is pleased to announce USP.
USP is different from all forms of control that have come before. USP allows the decoder to pick up the DCC signal even when there is no electrical contact to the rails. Gone forever are jerky operation caused by poor electrical pickup.
There are two parts to operating with USP. The first part is a decoder that uses USP technology to pick up and decoder the DCC track signal. The second is a smart power module that powers the decoder while it is operating on dirty track. The size of this power module depends on the amount of time the locomotive needs to be powered while on dirty track. For N and HO scales, with their efficient motors, the storage module can be small. For large scale outdoor railroading where dirty track is much more frequent the power module will be larger.
Because the power module and USP technology are now on board the locomotive, space consuming items such as flywheels are no longer needed and the decoder becomes an electronic flywheel.
DCC decoders with USP are totally compatible with all existing NMRA DCC systems and requires no changes to your existing wiring or control system. Locomotives and rolling stock equipped with USP act the same as any other decoder equipped models with the exception that poor pickup and dirty track will no longer be an issue to smooth and flawless performance.
In addition, since decoders will now be able to receive all DCC packets independent of dirty track or poor electrical pickup, the repetition rate for DCC packets can be reduced which will open up wide new possibilities for DCC operation.
There is more info Here