UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Different Dolby B / C Calibration Standards

Ted Kendall · 3rd May 2019, 6:05 pm

No, although I think Dolby Level for cassettes was 200nWb/m and that for open reel at 250, if memory serves. Some NAD decks had a thing called "play trim" which was meant to compensate for HF losses on incoming tapes and bring the Dolby into the sweet spot.

Cassette machines in general and Dolby machines in particular were always pushing the limits of available technology, and undoubtedly some manufacturers were more careful with line-up than others. Azimuth was always a variable feast, too - it was uncommon for two machines to match, and many machines gave a different answer if you removed and re-inserted the cassette. Fascinating as I have to admit they are, two comments from the Sounds Good programme in the 70s stick in my mind - one was a dealer admitting that the hi-fi cassette was "a fluke" and John Longden, the EIC of Radio London, giving his opinion that all the refinements were meant to make something that was basically rather horrid work.

Admittedly, Revox, Nakamichi and one or two others achieved this, but even they struggled with Dolby C - I don't think I've ever heard a Dolby C cassette recording which didn't display artifacts. B, proprely lined up, could actually work well. C was all right E-E, but once the tape was introduced into the chain, things went awry - it was just too finicky on line-up.

3rd May 2019, 6:05 pm	#3
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Different Dolby B / C Calibration Standards No, although I think Dolby Level for cassettes was 200nWb/m and that for open reel at 250, if memory serves. Some NAD decks had a thing called "play trim" which was meant to compensate for HF losses on incoming tapes and bring the Dolby into the sweet spot. Cassette machines in general and Dolby machines in particular were always pushing the limits of available technology, and undoubtedly some manufacturers were more careful with line-up than others. Azimuth was always a variable feast, too - it was uncommon for two machines to match, and many machines gave a different answer if you removed and re-inserted the cassette. Fascinating as I have to admit they are, two comments from the Sounds Good programme in the 70s stick in my mind - one was a dealer admitting that the hi-fi cassette was "a fluke" and John Longden, the EIC of Radio London, giving his opinion that all the refinements were meant to make something that was basically rather horrid work. Admittedly, Revox, Nakamichi and one or two others achieved this, but even they struggled with Dolby C - I don't think I've ever heard a Dolby C cassette recording which didn't display artifacts. B, proprely lined up, could actually work well. C was all right E-E, but once the tape was introduced into the chain, things went awry - it was just too finicky on line-up.