Conference napalm::commusic_v1

    Hmmmm.....
    
    My SWAG is you should have no problem. Dolby B works by boosting
    a set of frequencies around the same point that the hisssss lives at.
    (Methinks it's somewhere in the 8-10Khz range.) By boosssting thessse
    frequenccciesss during recording, it'sss able to cut them on playback
    abd take a few db of hissssss with it, leaving you with what you ssstarted
    with minus some his...
    
    dbx works by CoMpAnSiOn (compression-EXPANSION), compressing a signal
    during encoding and EXPANDING IT ON PLAYBACK with the intent of
    pushing the noise floor d
                              o
                                w n.
    
    Unfortunately, I have another SWAG. It seems that to be most effective,
    you'd want the signal to go through the following processing...
    
                      1.  Dolby encode
                      2.  dbx encode
                      3.  dbx decode
                      4.  Dolby decode
    
    I bet your deck will force the opposite (Which will probably work
    just as well.)
    
    If you can try it out first, go for it. Nuthin's gonna smoke...
    
    Edd
              

	Thanks, Edd.  Anybody else have other input?

	The idea of DBX being a compander, I was wondering if it can be used in 
lieu of a compresser/limiter?  Are they too different, or are they the same kind
of curcuitry but preset in a different configuration?  Am I off the wall (as 
well as too cheap to buy both)?

	Dan

    
    I answered your question in AUDIO. I tend to disagree with Edd,
    I think the two systems will interreact. Dolby B IS a companding
    system, although it is bandwidth-limited to the upper 10KHz of the
    audio band. Two companders in the same loop spell trouble to me.
    
    The dbx unit your thinking of, the NX-40? is non-adjustable. If
    you mess with the calibration controls to allow use as a compressor,
    it will have to be recalibrated to be used as a NR unit. It wasn't
    meant for use as an effects device. If you want a cheap compressor
    for your X-15, get a dbx 163x, they're about $120 new.
    
    Good luck with your low budget studio,
    
    CdH
    

    THAT won't work. Companders are one way devices. They make the signals
    on either side of a given point go further in the same direction.
    dbx, on the other hand, is a two way system requiring encoding and
    decoding. Their purpose is to effect some component (hiss) that
    was not part of the original signal.
    
    Edd

    
    Chris is correct in stating that dolby B is a companding system,
    though not necessarily in the vien we normally expect.
    
    I'll perform an experiment over the weekend....
    
    I'll tape something using dbx and dupe the *undecoded* signal to
    dolby b. Then I'll play that back, decoding the dolby and dupe the
    result. This will then be played back as *decoded* dbx. Given the
    fact that the tape hiss will increase due to the two extra genera-
    tions of tape, the result should (if I'm right) be quiter than 2
    dolby dupes and show no other effects....
    
    Can you wait till monday?
    
    Edd
    
    

	Monday should be no problem...

    We tried it...
    
    The source material was the 1st minute of Alan Parson's "Stereotomy"
    CD. This was recorded on a TDK SAC-90 with dbx. The *undecoded*
    dbx tape was then dubbed to a second SAC-90 set to record with
    Dolby B. Predictably, this second tape was unlistenable due to the
    characteristic 'breathing'.
    
    The Dolby B tape was then transferred back to the dbx deck. The
    Dolby was properly decoded and the dbx was left off. It was still
    unlistenable. The dbx was then switched in. *Most* of the breathing
    disappeared (not a good sign). The tonal balance in the mid to high
    end appeared unaffected, taking into consideration the fact that
    this was a 3rd generation tape. Tape hiss was increased as you would
    expect for a dubbed dub. Despite it all, there was still an obvious
    pumping as the noise floor changed.
    
    Though the high end balance seemed acceptable, I surprisingly found
    the lower midrange to be the most seriously affected band. This
    area was decidedly emphasized. (5-6 db?) This may have been an
    abberation in the frequency response of one of my decks....
    
    Given the fact that there was obvious (though not aggravatingly
    so) breathing, I'd have to modify my opinion. Try it, but listen
    *real* carefully.
    
    Edd
    
    
    

RE Note 748.7 by JAWS::COTE 

	Thanks, Edd, for going through all that.  While I've seen the term
'breathing' used in discussions of dbx, I'm not entirely sure what it means.
I'm sure if I heard it, I'd understand.  It sounds like I would do just as
well to leave the dbx unit alone.

	Dan

    'Breathing' sounds like tape hiss that follows the signal level...
    
    No level:== not much hiss (probably just what's on the tape)
    Low level:== Big hiss
    
    It's a result of the companding process. As the signal level changes,
    you can hear the hiss level change also. The sound resembles that
    of someone breathing...
    
    Edd

    um.  It's a result of the decoding circuitry trying to
    "make sense" of the signal in the bands of concern....
    
    Companding is a function of (usually) the integrated (smoothed)
    full-wave rectified signal. Unfortunately, real-time "smoothing" takes TIME.
    Sort of a VCA where the Voltage control is the 'victim' of dramatic
    level changes...cant seem to 'catch up'. Noticable on certain 
    classical pieces more easily (good test cases).

    darn old tape hiss.    No great analog solution yet....

    ron
    

    One last note about external noise reduction with cassette/mixers...on
    the X15 and most cassette/mixer units there is no way to insert the
    noise reduction except external to the mixer.  In a system of
    separates, the NR goes between the mixer and the recorder.  On an
    X15 while you can add NR to the signal at the input if you want
    (with all the caveats mentioned in earlier replies) there is no
    way to DECODE the NR before you remix....that is, you would have
    to decode your stereo mixdown.  Anyone who has tried something of
    this nature will tell you that decoding encoded tracks which have
    been remixed will result in horrible side-effects.   Stick to the
    Dolby in your X15, just use common sense and the noise won't be
    too bad....I've been recording for years without NR and it certainly
    is possible.  What do you suppose people did before Dolby was invented?
                                                

    
    	Re - .11
    
    	Yeah, I agree - what did they do??  You can always ride your
    source material by hand with a graphic eq - you know the song -
    just push 'em down when there's no high freq content. Sorta like
    a manual DNR.
    
    	I have a Phase Linear Autocorrelator. But have yet to try it
    in a "mixdown" situation. It should do real well. There's one for
    sale in the little audio repair shop across the street from the
    Somerville Theatre. He wants just under $100.00 for it.
    
    	I'm beginning to notice that these "processors" mess with the
    soundstage somewhat. The AutoC does that.
    
    	JJJ
    

    What did people do pre-Dolby ?
    
    Used ultra-clean TUBE preamps and amplifiers, and ran tape at 15
    to 30 inches per second, that's what.
    
    karl

    Wasn't dolby B Thomas's answer to the new problem caused by those
    infernal cassette decs?
    
    Edd

    
    It was Ray not Thomas, and it (in B form) was for consumer cassette
    decks. Dolby A is a studio, full-range system that's still in use.
    There's a new version of this who's name I can't remember right
    now, that's supposed to make analog rival digital in terms of
    signal-to-noise and dynamic range.
    
    CdH
    
    

    	re .15	>supposed to make analog rival digital in terms of
    >signal-to-noise and dynamic range.    

        	I think the name is (sounds like...)
    
    
    	Pea Sea Emm
    

    
    Re: .16
    
    PCM is digital encoding on analog tape, not a NR system. And it
    isn't HX Pro either. Guess it's time to pull out the old Mix magazines
    just to save face here.
    
    CdH
    

    Well, since we're digressing I might as well add a reply that may
    be of interest - I saw an interview with Thomas Dolby - it seems
    that Ray Dolby is trying to sue Thomas for using the "Dolby" name 
    in the music arena.  What a PIA...
    
    Todd.
    

        They settled out of court; neither party will defame the name,
        no cash has exchanged hands, and Thomas won't do adds for stereo
        equipment.

        R

    
    	Well, this has nothing to do with Dolby/DBX, and I'm pretty
    sure it's been discussed before, but after muych searching I have
    not found it, but - i'm having horrible bleed-thru problems with
    my Tascam-424.  I've tried reduced levels etc to no avail!  Any ideas?
    
    	bob