Are there any tell-tales in an Audacity waveform that give a clue that Dolby B was used in a source recording?
I’m restoring some old Cassette recordings for a friend who has long since forgotten whether or not it was used. They are all past their best and a little “dull” so its difficult to just listen for them being over “bright” (the usual solution). I’m never going to be able to make them as good as they once were, that’s way beyond my expertise, but I’ll give the treble a little lift to compensate for the dullness but it’d be nice to start with the correct Dolby setting…
As you noted, Dolby B tends to exaggerate the brightness of a recording, but tapes tend to become dull with age. I still have a lot of old cassette recordings (recorded with Dolby), and in most cases they sound best played with Dolby off, and then apply a little bit of Noise Reduction to reduce the hiss.
Be careful not to apply too much noise reduction because it will cause unpleasant metallic “chirps” that are more distracting than a bit of hiss.
I don’t think so… The frequency content (and audio content in general) will vary a lot anyway so it’s hard to tell.
Maybe with some deep statistical analysis, but that would be like a PhD project with MATLAB, or something. 
Since you say they are all a little dull, maybe you can try with and without, and then boost the highs to see which way sounds best.
As you probably know, a lot of people used to turn Dolby off for playback as “standard practice” because cassettes tended to have rolled-off highs. (I didn’t… I used it “properly”)
Thanks for the feedback guys, I suspected there weren’t but you don’t find out if you don’t ask!
This won’t be helpful, but something I just remembered…
I think it was on another forum where someone said there were CDs where the Dolby-A decoding wasn’t applied to the studio tapes when digitizing (and they were overly bright). I don’t know if that’s true but they were trying to make a digital Dolby-A decoder. It’s probably impossible to do properly because the (analog) levels have to be calibrated and there’s no known-fixed calibration between analog & digital levels.
Yeh - I think I have my answer to this one… …“No there isn’t any (usable) tell-tale”, I’ll just have to use my ears and apply my best guess. I don’t need a decoder, my cassette deck is equipped with Dolby B. There’s absolutely no danger that anything more sophisticated has been used when making the source tapes…
I appreciate your input, however
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