Originally Posted by
Rudy Kleimann
Burwen/KLH also made a very fine "Dynamic Noise Filter" model DNF1201A, a high-frequency noise supression that shut down the highs below a certain adjustable threshold. It did this on a 'sliding' frequency hinge point that varied up and down according to the frequency content of the signal above the threshold level, instantly opening only the frequency ranges that actually contained material and shutting down all frequencies above the frequencies of the signal content. This made for a very effective single-ended noise reduction system that was great for tape hiss, vinyl surface noise, and hiss in FM broadcasts. It, too, was easy to set and very benign in action. And, unlike Dolby B and C which boosts the high frequencies during the recording, or the much more aggressive DBX type II which is totally unnatural and preactically unlistenable in its encoded form, this system works with normal recordings, therefore usable on any program material that was noisy. I own two of these, one branded Burwen Research and the other KLH Burwen Research.