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Hello, Jay,<br>
<br>
As you may recall, Azimuth has become an issue with me. I hope
you're happy with my two slides on pages 27 and 28 of my Powerpoint
on the subject at the Culpeper Archiving Conference in June 2018.<br>
<a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/cvtfcqleoemov76/HESS_EB1_Azimuth_AES_2018_PowerPoint_v_001-00_reva.pdf?dl=0">https://www.dropbox.com/s/cvtfcqleoemov76/HESS_EB1_Azimuth_AES_2018_PowerPoint_v_001-00_reva.pdf?dl=0</a><br>
The two azimuth audible demos are at the following URLs in the order
presented:<br>
<a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/1aiyy10vgwdaipr/NM_Azimuth_Demo_Dragon_clip.wav?dl=0">https://www.dropbox.com/s/1aiyy10vgwdaipr/NM_Azimuth_Demo_Dragon_clip.wav?dl=0</a><br>
<a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/hf75z5nmbgfl2o7/JD%20Azimuth%20Demo_Dragon_clip.wav?dl=0">https://www.dropbox.com/s/hf75z5nmbgfl2o7/JD%20Azimuth%20Demo_Dragon_clip.wav?dl=0</a><br>
<br>
<br>
As to the levels, of course you are correct that the tape reference
levels should be set in the machine not ahead of it (rec level cal
and play level cal). My comment elsewhere is that you do run into
gain staging issues with dbx, but you don't see those with Dolby for
precisely the reason you mention.<br>
<br>
As to azimuth wander, I had two tapes and the best copies of the
program that could be found were the half-inch four-track loop-bin
running copies. There were two. One of them was reasonable, the
second had the worst wander I think I've ever seen on a tape. Of
course, the loop-bin masters were probably run to death before hand,
and the 1,3 and 4/2 track pairings didn't help. On this project I
tried to keep up with the gross changes as the tape went, but I
found I got a much better mono sum (I'm 99% certain they were
intended to be mono tapes) with running the "Azimuth correction"
function in iZotope RX. The Stereotool.com azimuth "strip chart"
display (page 24 of the Culpeper Powerpoint) went from full extremes
to barely moving. Of course, the azimuth correction doesn't and
really can't do much about the HF loss in the single track, but if
it can consistently time-align the tracks, then the mono sum will
have as good HF response as an individual channel (or almost). See
chart on page 21 of the Culpeper Powerpoint.<br>
<br>
Cheers,<br>
<br>
Richard<br>
<br>
<div class="moz-cite-prefix">On 2020-02-11 5:29 p.m., Jay at MRL
Support via ProAudio wrote:<br>
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cite="mid:625726203.20200211142947@comcast.net">
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<title>Re: [ProAudio] FeralA - Recordings released encoded with
Dolby A</title>
<span style=" font-family:'Times New Roman'; font-size: 12pt;">Hello
James,<br>
<br>
I'm not really a head fabrication expert, but it's approximate
like this: There were at least two ways of making multi-track
heads: one used milled metal side pieces into which the cores
were epoxied, and the whole thing either bolted or epoxied
together. The other used a jig to hold the cores together, then
epoxy was poured to hold it together without using any actual
side pieces.<br>
<br>
Glue together is a nice idea, but subject to the cores moving
around from the intended positions. So the former is subject to
less "drifting" of the cores, which causes gap scatter, but is
more expensive to produce. Ampex professional heads were usually
the former, consumer heads usually the latter. Other vendors
often used the latter. <br>
<br>
So if you want to know what the gap scatter is on your recorder,
you really need to measure the time delay between the several
tracks. And remember that you are measuring the sum of the
delays in recording and reproducing the tracks.<br>
<br>
The gap scatter is much more a time-delay problem than an
azimuth problem in the individual tracks.<br>
<br>
On Tuesday, February 11, 2020 at 10:00, you (James Perrett via
ProAudio) wrote:<br>
<br>
</span>
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<td><span style=" font-family:'times new roman'; font-size:
12pt;">With regard to setting the azimuth by summing to
mono and adjusting for maximum hf - I've heard people
say that there could be a problem if the head gaps on
each track are not in line with each other. I've not
experienced this myself as I've found that setting the
azimuth with a 15kHz tone using just one channel matches
the mono sum method well on the machines that I use but
I guess some manufacturers made their heads more
precisely than others. Have others experienced head gaps
being out of line with each other?<br>
<br>
On Tue, 11 Feb 2020 at 17:21, Bob Katz via ProAudio <</span><a
style=" font-family:'times new roman'; font-size: 12pt;"
href="mailto:proaudio@bach.pgm.com"
moz-do-not-send="true">proaudio@bach.pgm.com</a><span
style=" font-family:'times new roman'; font-size: 12pt;">>
wrote:<br>
</span>
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<td><span style=" font-family:'times new roman';
font-size: 12pt;">Here are three responses to
three different subjects that have expanded from
the original topic! <br>
I. There are so many ways that test tones at the
head of a tape could be different from the audio
on the tape. In the old days in some studios I
saw some visiting engineers lay down test tones
after the fact, on a different machine than was
used for the mixdown, as if that would help the
situation. <br>
We transfer engineers have developed a spidey
sense and often check and recheck the content to
ensure it has not changed from cut to cut. On
most machines, before making the transfer for a
new cut, you can put your finger on the side of
the tape to tilt it slightly, while listening in
mono to ensure the azimuth has not drifted, and
then transfer the new cut. </span></td>
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<br>
<span style=" font-family:'Times New Roman'; font-size: 12pt;">Agreed.<br>
<br>
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<td><span style=" font-family:'times new roman';
font-size: 12pt;">II. As for Bob O's comment
against the practice of doing elevated dolby
level, I agree there was a standard for 185, but
as people started to use elevated levels as high
as 6 dB over 185, I was seriously concerned
about running out of headroom in the Dolby gear
if standard dolby level was used, and so as a
practice, I see less harm in using an elevated
dolby level than to overload the Dolby processor
with too hot audio. I always recorded dolby tone
as well as 1 kHz @ VU. The Dolby 361 meters, as
Richard mentioned, were notoriously inaccurate,
I would put a sharpie mark on the real dolby
level on the meter, for what it was worth. There
was a Dolby tester that could be used for
accuracy of the dolby tone or I believe a test
point that could be checked. </span></td>
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<br>
<span style=" font-family:'Times New Roman'; font-size: 12pt;">Remember
that the Dolby process does NOT increase the level of the
high-level passages, only that of the LOW passages. And if you
record at higher level then 185 nWb/m, that increase should
happen AFTER the Dolby processor, NOT before it. So distortion
of the Dolby processor should not be a problem.<br>
<br>
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<td><span style=" font-family:'times new roman';
font-size: 12pt;">III. Dear John: <br>
So you set azimuth by looking at the bias. Are
you looking at two channels of bias? And how is
this superior to the tried and true method of
mono-summing the left and right audio channel
and adjusting for maximum high frequency
response, also checking by inverting the
polarity of one and going for a minimum as a
cross check? </span></td>
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<br>
<span style=" font-family:'Times New Roman'; font-size: 12pt;">In
my experience, the limitation on the accuracy of setting azimuth
is not the measurement accuracy (how high a frequency you use),
but the azimuth wander caused by tape slitting wander, and
wander of the tape in the transport guides.<br>
<br>
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<span style=" font-family:'times new roman';
font-size: 12pt;">Best wishes,<br>
<br>
<br>
Bob<br>
On 2/9/20 4:32 PM, John Chester via ProAudio
wrote:<br>
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<td><span style=" font-family:'times new
roman'; font-size: 12pt;">On 2/9/20 3:56
PM, Richard L. Hess via ProAudio wrote:
<br>
<br>
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<td><span style=" font-family:'times
new roman'; font-size: 12pt;">Also,
a funny story, the tones at the
head of that master tape caused
Alan a bit of a challenge...the
azimuth of the tone didn't match
the azimuth of the audio! </span></td>
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<br>
<br>
<span style=" font-family:'times new
roman'; font-size: 12pt;">Been there,
seen that. An assembled album master
may contain cuts that were recorded on
different machines, and sometimes even
in different studios. This becomes
really obvious when I'm doing Plangent
transfers. I can see when the bias
frequency and flutter profile change,
and I set azimuth on each cut by looking
at the bias. I have seen a master where
the head tones were recorded on a
different machine which didn't match
*any* of the music. <br>
<br>
When the album master is Dolby encoded,
and several different machines were used
for mixing, I can't believe that the
Dolby setup on all of those different
machines perfectly matches the head
tones. Fortunately the tape with the
head tones recorded on a completely
different machine wasn't Dolby..... <br>
<br>
-- John Chester <br>
<br>
<br>
<br>
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<span style=" font-family:'times new roman';
font-size: 12pt;">-- <br>
<br>
<br>
<span style=" font-family:'courier new';">[...]<br>
<span style=" font-family:'times new roman';">_______________________________________________<br>
</span></span></span></td>
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<br>
<br>
<span style=" font-family:'times new roman'; font-size:
12pt;">-- <br>
**********************************************************************<br>
* James Perrett<br>
* JRP Music Services, Hampshire, U.K.<br>
* Audio Mastering, Restoration, Recording and
Consultancy<br>
* Phone +44 (0) 777 600 6107<br>
* e-mail </span><a style=" font-family:'times new
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<span style=" font-family:'times new roman'; font-size:
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<br>
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<br>
<span style=" font-family:'calibri'; font-size: 9pt; color:
#c0c0c0;"><i>-- <br>
Best regards,<br>
Jay McKnight <br>
at<br>
Magnetic Reference Laboratory, Inc </i></span><a style="
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<span style=" font-family:'calibri'; font-size: 9pt; color:
#c0c0c0;"><i> <br>
Technical Information only: Sales information and
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</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Richard L. Hess email: <a class="moz-txt-link-abbreviated" href="mailto:richard@richardhess.com">richard@richardhess.com</a>
Aurora, Ontario, Canada <a class="moz-txt-link-freetext" href="http://www.richardhess.com/">http://www.richardhess.com/</a>
<a class="moz-txt-link-freetext" href="http://www.richardhess.com/tape/contact.htm">http://www.richardhess.com/tape/contact.htm</a>
Quality tape transfers -- even from hard-to-play tapes.</pre>
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