From: tonyb@juliet.ll.mit.edu ( Tony Berke )
Newsgroups: rec.audio.pro
Subject: Re: Does spaced omni ever really work?
Date: 29 Sep 92 13:58:13 GMT
	<5302@gold.gvg.tek.com>
Distribution: rec
Organization: M.I.T. Lincoln Lab - Group 43

In article <5302@gold.gvg.tek.com> chrisc@gold.gvg.tek.com (Chris Christensen) writes:

   In article <TONYB.92Sep24101640@titania.juliet.ll.mit.edu> 
   tonyb@juliet.ll.mit.edu ( Tony Berke ) writes:
   >I was over at a fellow netter's house the other night, and part of the
   >entertainment involved listening to a CD from some outfit called
   >"performance recordings" that contained an extensive series of
   >recordings intended to compare the stereo localization and off-axis
   >response characteristics of quite a few different stereo miking
   >techniques.

   Do you know if this was a disc who's ultimate goal was to support the
   recordimg technique that they (Ferformance recording) use?

I don't think they had any particular hidden motives at all.  I got
the distinct impression that they did the test because they were
interested in it, and thought some other people would be likewise
interested in it enough to pay some money for the disc.  They appear
to have been correct, given the amount of text that has been written
in response to my original posting about it!  The closest thing to an
editorial opinion that I could find in the whole thing was the fact
that the "example" pair they played first was Blumlein/Spaced Omni.
They used this pair to illustrate clearly the type of differences between
mikings that the text was trying do describe.  The main thrust of the
text was that the 12 loudspeaker sources were evenly spaced and had
a fairly uniform polar pattern, the implication being that an accurate
stereo miking system should make you think that you were hearing a 
reproduction of the original event.

   >The format of the test was to feed a sequence of clicks into a bank of
   >2" loudspeakers that were positioned in a horizontal line along a
   >wall.  Each speaker was, if I remember correctly, 8" apart, and the
   >line extended for about 10'.  The signal was switched from speaker to
   >speaker (between clicks) to cause the sound source to smoothly pan
   >back and forth along the line.

   I *like* the idea of using impulses for this kind of clinical
   evaluation, however, the venues I work are 30-60 feet wide!  I would
   be interested in experiments that were made at those distances.

Me too. 

   >The liner notes on this CD didn't tell you exactly what mics were being
   >used, but they claimed all the mics used were "studio grade", condensers
   >and dynamic, of various patterns.  There were demonstrations of ORTF done
   >with condenser and dynamic cardiods at various included angles, MS with
   >Figure 8, Cardioid, and Hypercardioid "mid" mics, dual and triple spaced omnis
   >at various distances from each other and the source, coincident cardioids at
   >various angles.

   I am leery of this kind of tests.  I would want to know what brand of
   mic was used.

   IMHO th tests should be done with the same switchable pattern mic so
   as to minimize the different sound qualities of the mics used......

Many of the mikings were tried with more than one brand of mic.  Although
the specific brands were not identified, the liner notes make it possible
for you to determine which tests used the same mikes in different patterns.

   This questioning in my mind refers me to  my first question, just what
   was the purpose of the tests,  what was the agenda?

Again, I don't think they had one.  There were no conclusions drawn in
the liner notes, just an invitation to listen, and have some fun.
They said that they didn't identify the particular mikes used because
they wanted people to concentrate on the configuration, and not get
hung up on convincing themselves that their particular $3000.00 stereo
mike sounded best.

   Please supply details on this CD so we can all check it out!

I'll try to remember to write the catalog number of the thing down and
post it.  For now, the label was Performance Recordings, the title was
something like "Stereo Microphone Test", and it was purchased at Tower
Records in Boston.

   Was there a "room sound" taken into consideration as far as
   preference? 

No, but I think one could infer a bit about room colorations from the
way the tonal quality of the clicks varied as the source moved about.
The room itself appeared pretty dead, however.  Perhaps that's the
biggest bias that the test had built into it -- Spaced omni's two
potential benifits ( uncolored room sound and great bass response )
were really of no value in this test, which rewarded precise image
localization and consistant frequency response within the main
soundstage.

Perhaps the test should be repeated by setting off a spaced series of
dynamite sticks on the stage of a large symphony hall, with an
audience.  This test would have a small bias against close-miking
techniques, of course ;-)