[Stephen]

As far as I'm aware, we'll what I can remember. Doesn't matter if a tape was duplicated with Dolby or not.

It's the player that decodes the dolby signal. So if the tape deck doesn't have the circuits for it then it won't have any effect.

All Dolby NR did was to reduce the tape hiss making the tape sound cleaner. Tapes were created to be a cheaper format, and inherently it needed Dolby to improve the quality of the recording playback. Dolby NR stopped being licensed in 2003 after pre-recorded tapes stopped being prodiced .

However in recent years some bands and artists have started to release cassettes of recent releases. No Dolby is around. However digital recordings and current ways to duplicate tapes does help reduce the hiss present. I have bought a few new tapes recently but never listened to them.