Noise reduction has nothing to do with the number of speaker channels, both A type and SR surround have the same Left, Center, Right and Surround set up.
SR has twice the noise reduction of A type, resulting in a much better signal to noise ratio. So you get the same number of channels in SR and A type but with SR the sound is nicer.
These articles explain the science of noise reduction quite well: http://www.dolby.com/ken/
In an older Dolby processors, the two different kinds of noise reductions are done on two different analog PC boards inside the unit. But since the Sony unit is entirely digital, the Sony people had to write a program to "mimic" that same signal processing.
You would probably be doing everyone a favor if you changed the text the SDDS displays. Check with your service guy first, but I'm sure he would agree.
Instead of "NR1," change it to read: "Optical Dolby A type (format 04)."
Instead of "NR2," change it to read: "Optical Dolby SR type (format 05)."
It is VERY important to select the right NR format for any given film. The differences between Dolby A-Type and Dolby SR are quite dramatic. Fortunately this has become less of a problem in recent years because Dolby A-Type is not used all that much (all films with a Dolby Digital track use SR on the analog track). The worst thing you can do is play a Dolby A-type print with SR selected on the processor, as this will result in "pumping" of low level dialogue, not to mention weird effects on frequency response.
This used to be a common problem with DTS-only films, because "DTS Stereo" = Dolby A-type, not Dolby SR (unless things have changed, have they Karen?).
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Ray Derrick
President
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