The Suhr unit is not it, but it's very similar to what I'm thinking of. I think somebody used the system here not long ago. Supposed to work pretty well, albeit not perfectly. I suspect all noise reduction/elimination schemes (outside of gates) based on filtering suffer the same side effect, where the lack of interference actually changes the original "tone" enough that it can be heard, since the noise itself changes the original signal due to interacting augmentation/cancellation.