Just about everything you'd want to know about National Semiconductor's no-preprocessing-required Dynamic Noise Reduction System. (And oh yeah...I definitely have the Keykeeper beat on long videos now! Sorry about the length and camera shake.)
After making this video, I realized that a couple of things were not well explained or covered at all. In addition to becoming the noise reduction standard for the MTS television audio system, dbx did see a fair amount of use in the professional audio market, particularly for wireless microphone systems.
Although it use in dedicated noise reduction devices appears to have been limited, DNR did find use in other places. I've seen a Recoton "FRED" stereo TV tuner device with it, and like dbx, DNR was also used in some wireless microphone systems.
Systems that did much the same thing as DNR also existed. If you want to see an example, watch my Symmetric Sound Systems noise reduction kit video:
• My Next Big Electronic...
Like other noise reduction systems, DNR feeds the audio signal not only to the actual noise reduction circuit, but also through a control path that analyzes the signal and takes action based on what it "sees". To prevent uneven noise reduction or corruption of the stereo "image", one control path governs the noise reduction effect on both audio channels at the same time.
I believe that everything I said in this video is reasonably correct. If you have a correction, please do feel free to post it as a comment.
I am looking for information on the Advanced Audio Systems company. So far, all I know is that its business license was revoked and that they did produce at least one other noise reduction device that is mentioned in a Chicago Tribune article from the mid 1980s:
articles.chicagotribune.com/19...
Another standalone device (not shown in this video as I don't have one) implementing the DNR system was known as the KLH/Burwen DNF1201A. These actually seem to be somewhat common. If you can't find any of these devices, National's DNR IC is still produced and readily available for a reasonable price. Plans exist online to build a circuit using the part:
wiredworld.tripod.com/tronics/... (warning: pop-up or under ads are likely!)
You may also wish to read the very comprehensive application notes on the DNR system:
www.national.com/an/AN/AN-384.pdf
www.national.com/an/AN/AN-386.pdf
www.national.com/an/AN/AN-390.pdf
Has anyone got some documentation for either the DNR System 911 or Archer 15-1278A? RadioShack did not have anything for the Archer device on their site and their technical support department was unable to find anything either. Please dig through your junk piles and let me know! (You do have junk piles, right?)
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