All About National Semiconductor's Dynamic Noise Reduction System

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:
http://www.youtube.com/watch?v=n_oiLuNq28Y

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 So far, all I know is that its business license was revoked and that they did produce at least one other noise reduction device that is mentioned in a Chicago Tribune article from the mid 1980s:
http://articles.chicagotribune.com/1985-03-15/entertainment/8501140895_1_came...

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:
http://wiredworld.tripod.com/tronics/dnr.html (warning: pop-up or under ads are likely!)

You may also wish to read the very comprehensive application notes on the DNR system:
http://www.national.com/an/AN/AN-384.pdf
http://www.national.com/an/AN/AN-386.pdf
http://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?)

Category:

Science & Technology

Tags:

• national
• semiconductor
• dynamic
• noise
• reduction
• DNR
• system
• 911
• GM
• Delco
• car
• radio
• dolby
• dbx
• anrs
• high-com
• archer
• video
• sound
• processor
• 15-1278A
• Symmetric Sound Systems
• audio signal restoration unit
• ASRU
• richard
• burwen
• LM1894

[james42519]

you know anything about tv? i can't seem to figer out what std, irc, hrc do on cable.

[uxwbill]

@james42519 HRC and IRC are both different types of signal modulation on cable TV systems.

[Matthew55904]

i odnt see a difference i can still hear what sounds like rain on both only different is there is no hiss but the rain sound dont change and what are metal tapes? they actually contain metal?

[uxwbill]

@Matthew55904 Hm. Another comment that was never brought to my attention. The rain sound belongs there and is a desired part of the recording. The hiss is not a desired part of the recording, and its absence is what you are supposed to notice. So you are on the right track.

All tapes contain "metal" (usually ferric oxide in a normal bias tape). Tapes advertised as "metal", "CrO2" or "high bias" used different metals in different formulations to produce a cleaner sound with less hiss and noise.

[james42519]

@uxwbill yeah i guess so. i can't tell what the difference is by changing them really. no manual of course.

[r0natello]

To my ears, the DNR seems to somewhat dull the upper harmonics of the guitar and vibes. It got rid of the hiss though!

[Lachlant1984]

@vwestlife I think Dolby Pro Logic II was introduced a bit earlier than 2000, like 1998 or something because I have Donkey Kong 64 which came out in 1999, and I'm pretties sure that game utilises Dolby Pro Logic II as a lot of video games do these days, I've not tried it because I don't have anything that can decode Dolby Pro Logic II.

[Lachlant1984]

I know this isn't really too relevant to this video, but I've noticed that on my iMac there's an Ambient Noise Reduction feature that works with the internal microphone, I've played with it a little bit but not extensively and it certainly works from the very short tests I've done, I'm not sure if it introduces negatively desired artefacts or not, but I'm not willing to really use it if it does.

[dogwomble]

DBX was not popular on _consumer_ tape equipment. However, it was extremely common on multi-track cassette systems, examples the Tascam and Yamaha 4- and 8-track recording decks.

[uxwbill]

@rmx77 Tapes encoded using Dolby B and the HX Pro system are not uncommon. There was a lot of support for the HX Pro system in later model tape decks. It only comes into effect when you are recording. Any cassette playback machine, whether it has HX Pro circuitry or not, will work perfectly to play back a tape made on an HX Pro-equipped machine.

[Matthew55904]

@uxwbill u should do what ive seen to other GM Stereos like that on ebay wire a AUX in jack to it that cuts radio signal when used so ur brother can play say a iPhone on it