Decode Dolby NR and Stereo from line level source

[Damien Taylor]

Hopefully the topic sums it up accurately enough. In my spare time I scan in films using a home made film scanner, the process is very much not real-time and I recover the optical soundtrack during post processing using the excellent AEO-Light software. Unfortunately at this time there does not seem to be any way to apply Dolby noise reduction either A or SR via software, I believe there might be ways to decode the 4:2:4 matrix but I've not tried yet.

I don't really want to buy any more equipment like an outboard NR decoder or an SDU4 but I do already have a CP55 with an SRA5 in my screening room.

My question is, in the spirit of DIY, is there any way to feed the CP55 a line level source and have it apply the NR and Stereo matrix decoding where I can tap it at the preamp outputs? My initial thoughts so far included bringing the line level signals with resistors down to the expected solar cell input but I have my doubts that this would work. I've also considered that the "mag" input is possibly line level but likely wouldn't apply NR designed for optical. If anyone has any ideas or has done this before please let me know!

[Gordon McLeod]

unplug the opical preamp and input you line level on terminals marked preamp out

[Steve Guttag]

You can use the optical inputs using 47K resistors, in series, on the + and - inputs (so 4 resistors total for stereo) but with the down side that you are now adding whatever noise inherent in the optical preamp plus an unwanted slit-loss correction circuit. In short, you're adding degradation to your source before applying NR. But it is certainly doable. Interrupting the Lt/Rt signal going to the SRA-5 would be preferred. Remember, you are unbalanced and you'll need to address leveling from your source as level matching is critical for Dolby NR tracking.

[Damien Taylor]

Thank you for the suggestions Gordon and Steve, sorry for the delay.