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  1. #1

    Tapes recorded with dbx

    Does anyone have any suggestions for using Audition to correct the sound from cassettes recorded with dbx noise reduction, played back on non-dbx equipment?

    *Background:* I've found a box of tapes of interviews I did on public radio back in the 80s, nearly all of which have dbx noise reduction. Wouldn't you know it, of course, I don't have a dbx tape deck anymore!

  2. #2
    Maybe somebody with more specific info will jump in here, but this may help:

    DBX used a 2:1 compression; that is, a program with 30dB dynamic variation would be compressed to 15dB. So the first thing you have to do is set up the playback system to give you a 1:2 expansion characteristic.

    I don't remember what the attack and release time constants were; you'll have to experiment to see what settings give you the least "knob twiddling" effect. Certainly they will be under 30ms.

    The DBX characteristic that will be hardest to imitate will be the RMS level sensing. Because of the aggressive compression used in the DBX system, level sensing was critical. Due to phase shifts at various parts of the record/reproduce chain, simple average or peak voltage sensing wouldn't have worked. The only voltage measurement technique that is immune to phase shift effects is RMS measurement, which is why DBX used it. That was their big "ace" which made the system work so much better than previous attempts.

    Fortunately, this isn't going to be as much of a problem for you because your recordings are voice only. Phase-shift problems are worst with wide frequency range. Maybe you'll get by.

    Try setting the system up for a 1:2 expansion and a 10ms attack/release. Twiddle the attack/release time until you find the setting which results in least obvious processing. Then try minor changes to the expansion ratio until you've got the most subjectively pleasing sound.

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