Country of Manufacturer: USA
Dynamic Noise Reduction works differently from other noise reduction systems as it does not rely on encoding the recorded signal. It should be considered as a filter for the playback process that eliminates hiss. Using a National Semiconductor LM1894 IC, it employs a sophisticated approach which is best explained in the source document below. Perhaps Richard Burwen was the inventor of this technology which appears to be open-source and he marketed his own device, the 1201A.
The system 911 was made by the short-lived Advanced Audio Systems International of San Jose California
Here’s a great document produced after much research…