Hey Charles, most of the Pro Dolby units (made by Dolby Labs) you'll see are type A noise reduction. The pre recorded tapes such as the Barclay-Crockers, are encoded with Dolby B. There may be a way to disable the extra filters and use an A type decoder, but that would be a lot of work and would really be best left to someone who knows their way around a decoding card. I believe that the 301 and the 330 were the only ones that did B type decoding. Both of these are getting pretty rare and from what I've heard, would still need modification to sound transparent. The Dolby encoded tapes, like we'd be playing, have a boost in the frequency range that the tape hiss resides. If you listen to them without a decoder, the hiss is there and an emphasis of that band of high frequencies will be present. For now, I'm listening to those tapes without a decoder. It's not super noticeable and once I get caught up in the music, I don't notice it at all. I've been meaning to do some upgrading of a consumer Dolby B decoder but I haven't had a chance to do any serious work on it yet. If you can hold on, I hope to have some good news for 4 track pre recorded tape collectors in the future.