Bob (K7JQ):
The NR algorithms seem pretty much the same between newer and older versions of the CLRdsp, with the exception of level adjustability and tone control. The NR has a "slow attack, slow release" adaptation time which seems to allow it to work well in tandem with a rigs own NR.
Regarding the utility of the CLRdsp tone control - I find it quite useful but not essential. Two of my units have it, the others do not. But this is all a matter of individual hearing characteristics and preferences.
Regarding cost - yes - these units are quite pricy. But I've yet to find any other NR system that can match them and they make even my old Kenwood TS-440SAT, with it's very noisy and fatiguing receiver, much easier to listen to.
The CLRdsp volume control is ESSENTIAL, BTW, as the radio volume control adjusts the audio signal level into the CLRdsp, and correctly setting this level is critical to best operation. So actual USER volume is controlled via the CLRdsp unit itself, which has a strong audio amplifier - much better than found on most radios. The radio audio level into the CLRdsp should be set just below the clipping level of the CLRdsp, which is indicated by an LED on the CLRdsp unit, then user volume is set via the CLRdsp volume control.
Brian - K6BRN