The OBORO workshop was aimed at giving
participants a historical and theoretical overview
of Ambisonic surround sound and a demonstration of
the hardware and software production tools that
can be used for Ambisonic. Without redoing the
comparative surround recordings that took place in
Austria and Germany in 2001 or redoing
the comparative study between
tetrahedral array-generated B-Format and native
B-Format, we thought that the introduction
of the Zoom H2 portable surround recorder in
September 2007 warranted some new comparisons.
This time around though, the "best surround
microphone system for 5.1" criteria would not
necessarily be the main interrogation for the
comparison, but rather if the price point of each
system is subjectively reflected in the timbre
quality and the directional encoding.
The Zoom H2 is $200 (including the
recorder), the AKG Blue Line native B-Format
assembly is around $2000 and the SoundField ST350
is around $8000. It's important to remember that
in the case of the native B-Format and the
SoundField, a recording system must be added.
The Zoom H2 has four cardioid capsules
arranged as a 90° front pair and 120° back pair
(240° from center front), an arrangement
reminiscent of the quad days of the seventies. A
native B-Format assembly has one omnidirectional
and two figure-8 (bidirectional) microphones to
directly generate the Ambisonic B-Format. A
SoundField microphone has four cardioid capsules
mounted as a tetrahedron producing an audio stream
called A-Format: the SoundField control unit must
be used to convert the stream to B-Format.
Although the Zoom H2 can be used as an
USB audio interface, it's in the first place a
standalone recorder and it was used as such: since
the H2 was the lightest system, it was put on top
of the microphone stand. The ST350 was under the
H2 and about 15 cm in front of it. The 3 meter
cable that comes with the ST350 meant that we had
to tape its control unit to the mic stand and then
run four line level cables to its recording
system, a Sound Devices 744T. The
native B-Format assembly was under the ST350 and
about 10 cm in front of the H2. The three mic
level cables out of this assembly were run to its
recording system comprised of two Metric Halo ULN-2 audio
interfaces connected to an Apple iBook G4 1.33 GHz with
OS X 10.4.10 and Steinberg Nuendo 3.2.1
DAW. The three recording systems were set to
24 bit and 48 kHz.
Three excerpts from the Livre d'Orgue de Montréal: Voix
humaine, Trio and Dialogue.
Robert Sigmund, organ. Featuring Hugues St-Gelais, tenor.
Apart from the spatial processing necessary in some cases
(B-Format decoded to Quad, Quad transcoded to B-Format and
B-Format decoded to stereo), no other processing was done
(EQ, compression, etc). The B-format RMS levels for the
AKG assembly and the Zoom H2 were matched to the ST350
B-Format RMS levels based on an organ sustained chord and
a RMS response time of 5 seconds. The output levels were
match by ear and should be within 2 dB of each other. The
B2G plug-in was used to decode
the B-Format to Quad, the Quad2B
was used to transcode the Zoom H2 quad surround to
B-Format and the B2Stereo
plug-in was used to decode the B-Format to stereo.
- AKG Blue Line native B-Format decoded to quad surround
(Zoom H2-like L, R, Ls, Rs, 90°/120°)
- SoundField ST350 B-Format decoded to quad surround (Zoom
H2-like L, R, Ls, Rs, 90°/120°)
- Zoom H2 quad surround (L, R, Ls, Rs, 90°/120°, original
- AKG Blue Line native B-Format (WXY, original three
- SoundField ST350 B-Format (WXYZ, original four channels)
- Zoom H2 quad surround transcoded to 1st order horizontal
B-Format (WXY, three channels)
- AKG Blue Line native B-Format decoded to stereo (110°
- SoundField ST350 B-Format decoded to stereo (110°
- Zoom H2 quad surround converted to stereo through 1st
order B-Format transcoding (110° width/0.75 hypercardioid)
On OS X, the latest versions of TwistedWave
Editor can open, play and process multichannel
OS X audio utility downloads
X Lossless Decoder (XLD):
utility for converting files between the following
formats: Wave, AIFF, raw PCM, Wave64 (.w64), MPEG-4 AAC
(.m4a), Apple Lossless (.m4a), FLAC (.flac/.ogg),
MP3, Ogg Vorbis, WavPack (.wv). Can also read
Monkey's Audio (.ape) and True
Audio (.tta). Files can be multichannel if supported
by file format.
Left: the front screen with the center channel
monitor behind it. On the screen is Wave Editor with an
Ambisonic file converted to 5.1. As far as sound
editors on OS X go, we also did demo the new
Right: the front screen again, but with the
modular environment of Plogue
Left: In OBORO's Studio 1, checking the
feasibility of mounting the three surround systems
on the same microphone stand. In the background, Klein + Hummel O 300
monitors that were used in an Ambisonic birectangle
rig for 3D sound reproduction.
Right: Testing the recording gear: on the table
are the Metric Halo ULN-2s that will be
used with the AKG Blue Line microphones.
There's also the MOTU 828 audio
interface that was used in playback for the
Ambisonic birectangle 3D rig.
Testing the recording gear: getting
around the menus on the
Sound Devices 744T.
The 744T will be used for the SoundField ST350.
We chose to disengage the 744T input level knobs and
to set it at a fixed input sensitivity: that way,
only the ST350 control unit is used for level
setting and the four line level input on the 744T
Left: a wide shot of the Grand Séminaire de
Montréal chapel before the recital. The black
bulge on the mic stand is the polypropylene
foam-wrapped and gaffer-taped ST350 control unit.
Right: The three surround pickups in the chapel.
Notice that the Zoom H2 is already running.
Compared to the other two systems, we have at
least fifteen minutes more of pre-recital
recording on the H2. This is the kind of detail
that must be taken into account when choosing the
SD card that will go in the H2: we used a SanDisk SDHC 4GB card.
Right: attentively listening to the recording in
the control room. Although the
Sound Devices 744T offers a "B-Format
decoded to stereo" monitoring mode, there are no
control for that mode. There was no way to modify
the decoding and, monitoring on headphones, we did
find the result to be quite narrow, to the point
of almost being mono.
By comparison, the stereo monitoring
in Nuendo was done with the B2Stereo plug-in that offered
much more monitoring options which proved to be more
useful in checking technical aspects of the
recording and more enjoyable for simply listening to