Eric, I think you misunderstood, perhaps because you have the luxury of working with professional machines.  On a tascam MS-16, there is no user-freind dbx adjustment, and so, you are stuck with whatever nominal level the MS-16 is expecting, that is to say, without dbx, you can choose ANY incoming signal -- within reason -- to calibrating input / record level.  However, the procedure you describe -- calibrating the dbx to the CALIBRATED tape machine -- is the reverse of what MS-16 users (et al) must do, which is basically to feed the machine a 1kHz level that, while switching the dbx in and out does not change and THEN calibrating the machine as per normal -- record level, eq, bias etc -- with the dbx OUT.

This misinterpretation was likely as much my fault as yours, it is sometimes difficult to be precise in a large article where repeated readings try to catch glaring errors -- after many tweaks via word processor -- sometimes minor "fuzzies" become more obvious once the text reaches process "wood stock."

Thanks for your feedback and comments.

ec

PS regarding frequency sensitivity,  dbx does not like frequency anomalies..  Again, these are correctable on a professional machine, but low frequency head-bumps have given dbx (as you say, relatively forgiving) a bad name, making the music or voice "pump" or seem darker than it should be.  I, for one, sucessfully used dbx with no problem.  Consider also that many people aligned machines at fixed frequencies, which, at the low end of the spectrum I am sure you will agree that a bass sweep is preferred.


At 10:03 AM 01/06/2001, you wrote:
Hi Eddie,

I've been enjoying your columns in MIX.  I have to disagree with you,
however, on the question about calibrating a tape deck with dbx in the
system (MIX November 2000, I'm a little behind).

Professional (Type I) dbx is a frequency-dependent system, which is
designed to be essentially neutral at 1 Khz.  Also, the front panel Bypass
switch (at least on dbx 180 and 150 series) is a hard-wire affair--no
circuitry is involved when bypassed.  dbx states that the Play and Record
level adjustments on the front panel are intended only to make monitoring
levels between dbx and non-dbx recordings match, and do not affect the
actual companding process.

My procedure for many years (which is also what dbx recommends) is to put
the dbx units in Bypass, then do a normal calibration of the tape machine. 
My last action is to put up a 1K tone from the console and switch the dbx
in and out of Bypass while adjusting the dbx's "Record" level control for
no change on VU meters at the deck.  To do the dbx's "Play" adjustment, you
can playback a 1K tone from tape, or put the machine in Input and send the
signal from the deck to another meter on the console, again looking for no
change between dbx IN and OUT.  That's it.  All this does is set unity gain
for the dbx so that bypass matches non-bypass.  It should have no affect on
the calibration of the tape deck or function of the noise reduction. 
Unlike Dolby Type A, dbx is a wonderfully forgiving system!

I do agree with you that it is a VERY bad idea to mess with any controls
inside the dbx unit!  You are also correct that the meters on the machine
will not deflect as much when using dbx, but this IS the level on the tape!
 In other words, you cannot set levels with the dbx out, and then switch it
in, because this would not represent the true levels being recorded.  One
must simply get used to the smaller meter deflection when using dbx.

Sincerely,


-- Eric Wenocur
Lab Tech Systems
Silver Spring, MD