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Thread: Tape Noise Reduction

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    Tape Noise Reduction

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    Is anybody making new dbx noise reduction units? Similar to the old DX-4D units?

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    Very doubtful, but there's a ton of dbx Type I and Type II devices available used. Search eBay. Given what dbx NR does, it's not hard to see why there's no new product. It wasn't all that great in the first place, what with mis-tracking, companding noise, response error multiplication and all. It was designed to be low cost, with a big NR number, but performance was less than stellar.

    The last time I had to play an old dbx tape, I simulated a decoder in a dynamics plug. Worked fine. If I was looking to add NR to an analog recorder for making new recordings, I'd shop for used Dolby SR.

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    I agree that dbx type II had companding artifacts and level issues when not calibrated properly but type I units were far less prone to those types of clearly audible problems. Dolby SR is a superior system for sure but it too requires very exacting calibration and costs close to $1000 a channel new. DX-4D's used, go for around $100 and do a decent job and are designed to work with -10db, unbalanced decks. Dolby SR is strictly a balanced, +4db system.

    Cheers!

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    Note that the dbx IC's int he DX-xD's are available from NTE.

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    There's a Dolby XP frame with 24 channels of SR on eBay right now for under $600, Buy It Now price. That's less than $25/channel for world-class NR. Yes, it's more channels than might be required, but what a deal! Keep the unused channels as hot spares. And, it's a long way from $1000/channel. If memory serves, there's enough input gain in an SR card to work at -10 and still calibrate. Output trims should go down as low as needed. As to calibration, it's not all that tight, there's a 2dB window, and, because of how SR works (Dolby A too), it doesn't multiply head bumps like dbx. For those unfamiliar with the term, narrow track heads like those found in 1/4" and 1/2" multi-tracks, have a low-end rise that relates to the narrow tracks - the "head bump". It's not always possible to equalize out, and can be several dB. Causes fits with dbx because it's a response anomaly between encode and decode. For dbx to track, the response between encode and decode should be as flat as possible, otherwise the 1:2 expansion goes a bit nuts and mis-tracks badly with audio in the head-bump zone.

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    If memory serves, there's enough input gain in an SR card to work at -10 and still calibrate. Output trims should go down as low as needed.
    FWIW, I could not get a Dolby 362 with CAT-22 A cards (CAT-280 do not fit) to calibrate at -10dB (I had mistakenly flipped the switch to L on my Otari MX5050BII-2)

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    Jeff is right again, when the DBX units are operating properly they sound amazing. Their is a HUGE diffrence in tape hiss / background noise when the unit is off compared to when it's engaged. I love all for of mine.

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