[ARSCLIST] Little azimuth trick: more explanation

["Richard L. Hess" <ArcLists@xxxxxxxxxxxxxxx>]

Some questions and comments came up about this technique on the Ampex
and ARSC lists. Thanks for the input. I should have elaborated more.

(1) 1kHz doesn't allow you normally to adjust azimuth finely enough.
Normal azimuth adjustment tones are 8kHz and 16kHz on an MRL test tape.

But, the "lever effect" of a wider spacing allows more resolution
from the 1kHz if you use the wider-spaced tracks.

By Lissajous nulling, I meant a single straight line.

(2) There was no stereo material--it was all single track stuff.
Guitars and vocals.

The tape was played on the APR-16 with essentially brand-new (NOS)
Applied Magnetics heads.

I used the technique to check my alignment on the 8-track 1-inch
Applied Magnetics heads to an MRL test tape and it worked well
vis-a-vis the azimuth setting section. I tried a few different track
pairs and it seemed fine.

Of course, the original record head could have gap scatter and if
you're adjusting way far from test tape null, that might be bad. But
it might still be a useful trick--especially if you look at different
track pairs.

The other thing, of course, is listening to cymbals, etc., for
"tizz". and doing it by ear. What I really love are noisy record
electronics. You can tune for maximum hiss on the tape in absence of program!

Mono compatibility is no better a test as gap scatter affects that as
well. <groan>.

Nothing is perfect, it's just another tool.

(3) I should have pointed out that I had already aligned the head to
the MRL test tape, tuning for maximum amplitude and then nulling.
Using maximum amplitude off the 1kHz did not provide a definite point
because it was a 15 in/s tape and the 70 mil track width doesn't
provide that much attenuation at 1kHz over a degree or two. I was
trying to fine-tune the azimuth to the particular tape.

It should be pointed out that I was rocking the azimuth screw
probably +/-30-45 degrees with knowledge of where the MRL test tape
center was. (like a cruder version of the lovely calibrated PB
azimuth knob on one of my A810s which goes through +/-40 units over
about a 300 degree range).

Other azimuth notes.

Also, when I do new azimuth settings I do look at different
frequencies to see that it isn't the wrong null. My first 8-track
head at 3.75 in/s did that to me, I was off enough to have it flip
back and forth--without a noticeable level difference because of the
very narrow tracks (21 mil).

Another point: many full-track mono tapes at 7.5 in/s have enough
"warp" to them that playing them back with a full-track head will
cause variable high-frequency response due to dynamic azimuth errors.
Instead of using the 240 mil full-track head, one can often get far
more stable frequency response using an 82 mil NAB play head at a
small loss of S/N ratio.

Cheers,

Richard


Richard L. Hess                           email: richard@xxxxxxxxxxxxxxx
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