From: chrisc@gold.gvg.tek.com (Chris Christensen)
Newsgroups: rec.audio.pro
Subject: Re: Does spaced omni ever really work?
Date: 28 Sep 92 19:12:29 GMT
Distribution: rec
Organization: Grass Valley Group, Grass Valley, CA

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?

>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.

>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......

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

>The playback system consisted of some medium-sized KEF tower speakers.
>The room was a bit small, but the speakers were about 8 feet apart, and 
>the listening position was about 8 feet from the baseline between the
>speakers.

>While I'm not sure what my friends and neighbors are going to think when
>I trot this CD out at my next party, I must admit that I found it quite
>fascinating.  There were very un-subtle differences to be heard between
>the various setups.  Some of them produced good enough imaging on the
>system we were listening to that we could easily track the exact location
>of the clicks as they bounced around the room.  On the better setups,
>the clicks appeared to move an even amount each time (which is consistant
>with the even spacing of the source speakers in the original recording),
>and the tonal quality of the clicks remained nearly constant as they
>panned across the soundstage.

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

>Of all the combinations presented, the mikings that performed the absolute
>*worst* were the spaced omnis.  The image was completely crowded towards the
>speakers most of the time, and in the space of three or four clicks
>(ie, 16 to 24 inches in the original recording space) the image would
>zoom from one side to the other.  The triple spaced-omnis didn't sound
>much better, and they did worse as far as phasiness.

I am not surprised!   I *think* that I would have predicted this kind
of sound from spaced omni's but I am also very convinced that
amplitude stereo is the best compromise!  :-)  I have had so much
sucess with the technique.  Oh and for the "record"  I have done this
with good cardoids as well as PZM's....

>In my one listening, I seemed to like the sound of the MS (cardioid
>Mid mike), Blumlein, and ORTF (cardiod, 110 degrees) mikings the best.
>I'm going to have to listen a few more times, preferably under blind
>conditions, before I can say which one I like the best.

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

>The coincident cardioids were so-so, but man, those omnis sounded like
>dirt! 3 feet apart, 5 feet, ten feet, six feet from the source, ten
>feet, two mics, three mics, YUCK!

When people talk about coincident cardoids I have to ask the actual
configuration.  Do you know if the capsules were "tip to tip"  or in
an over and under configuration.

I have done coincident over and under recordings that I really liked
and blended in well with my triad array.

I have been forced to use a tip to tip recording and I found that that
configuration had a hot center and little pickup to the edges of the
ensamble.  Fortunately the session was multi tracked with my PZM array
on a coupla channels.  I was abe to use the tip to tip mic's for a mono
center channel and my PZM's for life outside the center.......And some
really nice room sound.

>So what do you folks think?  My personal experience with spaced omnis
>is quite consistant with what I heard on the CD; I always get a hole
>in the middle and/or super-wide central images, and exagerated motions
>if anyone moves around center stage.

>On the other hand, I know that many engineers absolutely swear by a
>pair of B&K 4006s' hanging on a bar somewhere, and consider it the
>ultimate method for miking classical music.  Certainly B&K does!  What
>gives?  Did the producers of this CD mess up, have I screwed up, or
>are a lot of people fooling themselves as to what constitutes good
>imaging?

I agree with the discriptions of your observations.  I have listened
to recordings that *sounded* just like what you described.....

And I have listened to B&K's demo CD that does sound really fine.  I
guess one has to do what one feels is the right choice!

-- 
Chris Christensen                  The opinions I express are my own,
chrisc@gold.gvg.tek.com            and sometimes they are wrong!
916-478-3419 FAX 916-478-3887      After all, I *AM* only human.
Newsgroups: rec.audio.pro