        A comparison of the CoreSound Tetramic (CS 2050) 
      and a pre-series prototype of the Soundfield ST450.


      Jörn Nettingsmeier <nettings@stackingdwarves.net>
                    January 2011

Thanks to Soundfield Ltd. and S.E.A. Vertrieb & Consulting GmbH for
providing me with an ST450 for testing.

The Tetramic was recorded in A-Format and processed with Fons Adriaensen's
Tetraproc using the custom filter coefficients provided by CoreSound. 
The ST450 went through its preamp/converter box, which produces B-Format.
Both mics were co-incident, the ST450 mounted upright in its cradle, and
the Tetramic on top, in end-fire mode. They were recorded through an RME 
Micstasy with digitally controlled and matched gain, via ADAT through a 
Focusrite Saffire PRO26, to a Linux Audio workstation running Ardour.
The tracks have been roughly matched for equal loudness and rotated for
congruent localisation by ear.


All files are classical first-order B-format 24bit WAV at 48khz.
If you want to listen to them on stereo speakers, you can either use a UHJ
encoder, or a virtual stereo microphone. Both are available as LADSPA
plugins for Linux and Mac users as part of Fons' AMB plugin package. For
users of that other operating system, Google is your friend.
For serious A/B comparison, you should probably import each pair of files
into some DAW and play it back in sync while switching between the mics. 
For recreational listening under Linux, try starting JACK and AmbDec with
a suitable first-order decoder, and then use

	mplayer -channels 4 -ao jack:port=ambdec <filename>

.

*.*

First, two brief excerpts from a concert by "The Kites", a recorder ensemble
from Germany. The concert was part of the Montag-Tontag series at the
Kunsthaus Essen, a very small location that holds about 40 guests if you
squeeze them a bit. Way too close-miked for recorders, directly in front of
the stage, about 1.5m away from the musicians, at standing ear-height. 
And of course the acoustics are quite hostile to recorders, so Fons'
zita-rev1 had to help a bit. Still too direct for my taste, but good for 
comparing mic performance.

Ye olde Englishe musicke, with some very neat ad-libbing over "Pastime with
Good Company":

The_Kites-Three_Pieces_from_the_Court_of_Henry_VIII-CoreSound_TetraMic-24bit-48k.amb
The_Kites-Three_Pieces_from_the_Court_of_Henry_VIII-Soundfield_ST450-24bit-48k.amb

Dave Holland's "Conference of the Birds". The Petzold bass flute was gently
amplified using an AER acousticube amp on stage. Something apparently bumped 
into the mic stand during the performance, thus a GLAME 5-pole highpass at 100Hz
was applied to both mics. Same reverb settings as before.

The_Kites-Conference_of_the_Birds-CoreSound_TetraMic-24bit-48k.amb
The_Kites-Conference_of_the_Birds-Soundfield_ST450-24bit-48k.amb

You will notice that the applause is louder on the rear left - that's how
the audience was seated.

*.*

Next, a 12-minute free improvisation by Vincent Royer on viola, Stefan Werni on
double bass and Thorsten Töpp on classical guitar. Same location, roughly
the same microphone position. No amplifiers - yes, that _is_ a weapons-grade
double bass. Beautiful collaboration with a keen sense for space and tone - 
give it a spin even if the word "free jazz" gives you the creeps, chances
are you'll like it. In any case, it's a great test signal.

No artificial reverb this time, the Kunsthaus works quite well for this kind
of intimate music.

Royer-Werni-Töpp_Improvisation_#3-CoreSound_TetraMic-24bit-48k.amb
Royer-Werni-Töpp_Improvisation_#3-Soundfield_ST450-24bit-48k.amb

You should hear the viola to the right, the double bass in the center, and
the guitar to the left.

*.*

My private conclusion:

The ST450 is quite bassy and warm, which can be nice but it's not how I like
my microphones. However, it's easily tuned to taste with some gentle EQ, and
I can see how the basic sound would appeal to most musicians and location
recordists.
The Tetramic does an amazing job for the price, if and only if the music is 
loud enough.
I have no clear preference for the sound of either, although the ST450 is
nicer to tricky instruments such as strings, or voices.
But if you need better signal-to-noise ratio, there's no way around the
ST450. Of all the Soundfields I have used so far (a DSF-1, a Mark IV, an
ST350), the ST450 has the best localisation.
Unfortunately, it will set you back by about 4k pounds, which makes the
Tetramic look really good in comparison. But that price includes a very good
beltpack-sized matched preamp with stereo monitoring and B-format line outs,
and a very roadworthy, professional package with a sturdy balanced multicore
and LEMO connectors (as opposed to the flimsy nightmare that is the
Tetramic's cabling).
If you want it quiet and precise, there's no match for the ST450. As soon as
I have the cash, I'll get one. But it may well be the Tetramic that earns it :)