Ambisonic Studio Ambisonic
   
Comparative Surround Recording 2008  
 
 

Line Audio QM12i

 

In October 2008 was held a surround sound production workshop (PDF) at OBORO in Montreal. On October 12, we recorded an organ recital by Yves-G. Préfontaine at the Grand Séminaire de Montréal chapel using two surround microphone pickups: a SoundField ST350 and a Line Audio QM12i quadraphonic microphone. Here is an account of the recording session with pictures and audio samples.

Like in October 2007, 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 Ambisonics. From its inception, Ambisonics was always an inclusive technology and although the SoundField microphone is often viewed as "the only Ambisonic microphone", any audio signal can be encoded to Ambisonic B-Format. Back in the late seventies, the Neumann QM69 quad microphone was planned as a source of B-Format, once its quadraphonic signal was converted. The QM69 hasn't been in production for a long time, but nowadays Swedish microphone manufacturers Pearl and Line Audio Design are both offering a quad mic model. For the October 12 recording, we had the opportunity to try out the Line Audio QM12i along with a SoundField ST350.

The Line Audio QM12i microphone is around $1000 and the SoundField ST350 is around $8000.

The QM12i has four cardioid elements arranged at 90° from each other to uniformly cover a 360° horizontal field. It's interesting to note that each cardioid element in the QM12i is in fact made up of three smaller capsules. The 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.

As it can be seen from the following pictures, we also installed a Zoom H2 surround microphone/recorder, but last minute formatting problems meant that it recorded the recital at different settings than the main recording device. We will not use the result for this review then: read the 2007 report for the Zoom H2 performance in similar conditions.


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Highslide JSOBORO's surround sound control room   The workshop at OBORO's surround sound control room. Dynaudio Air 20 monitors are positioned in typical 5.1 fashion with left/right at 30° and Ls/Rs at 110°. On screen is a picture of the 1976 prototype SoundField microphone revealed by Michael Gerzon himself. The picture is from the Michael Gerzon Photos website.
 
Highslide JSOBORO's control room screen showing Apple Grapher   Highslide JSOBORO's control room screen showing Plogue Bidule   Left: in OBORO's surround sound control room, on screen is Apple Grapher. It's used in the workshop to demonstrate the design of virtual microphones.

Right: the front screen again, but with the modular data flow environment for audio of Plogue Bidule.

 
Highslide JSIn OBORO's Studio 1, checking the recording the gear.   In OBORO's Studio 1, checking the recording the gear. The Line Audio QM12i is installed on top the mic stand and about 10 cm in front of it. The four mic-level cables from the QM12i are connected to two Metric Halo ULN-2 audio interfaces. The ST350 is under the QM12i and about 15 cm in front of the mic stand. The four line-level cables out of the ST350 control unit are connected to a RME Fireface 400 audio interface. The Metric Halo and RME audio interfaces are connected to an Apple MacBook Pro 2.4 GHz running OS X 10.5.5 and Steinberg Nuendo 4.2.2 DAW. The audio interfaces share the same wordclock and are grouped with the Mac OS X Aggregate Audio Device feature to present only one audio interface to the recording software. The recording is done at 24 bit and 48 kHz.
 
Highslide JSThe Double MS assembly   As an add-on to the main recording setup, a Double MS assembly will also be installed. This Double MS assembly is comprised of a Schoeps CMIT5 U, a Schoeps MK 8 and a Schoeps CCM 41. The Double MS will be recorded on a Aaton Cantar-X.
 
Highslide JSThe Line Audio QM12i with its grille removed.   The Line Audio QM12i with its grille removed: each capsule triplet make a cardioid element.

Line Audio QM12i microphone courtesy of Etienne Bovo.

 
Highslide JSSetup in the Grand séminaire de Montréal chapel   Highslide JSSetup in the Grand séminaire de Montréal chapel   Highslide JSThe ST350 control unit taped to the stand.   Setup in the Grand séminaire de Montréal chapel.

The 3-meter cable that comes stock with the ST350 meant that we had to tape its control unit to the stand.

 
Highslide JSThe two raised microphone stands.   Highslide JSThe two raised microphone stands.   The two microphone stands once raised.
 
Highslide JSThe main stand with the three surround microphones.   Highslide JSThe secondary stand with the Double MS assembly.   Left: the main stand with the three surround microphones.

Right: second stand with Double MS assembly.

 
Highslide JSRecording and monitoring the QM12i and the ST350.   Highslide JSRecording and monitoring the Double MS assembly.   Left: recording and monitoring the QM12i and the ST350.

Right: recording and monitoring the Double MS assembly.

 
Highslide JSThe MacBook Pro with Nuendo recording the QM12i and the ST350.   Highslide JSThe Cantar-X recording the Double MS assembly.   Left: the MacBook Pro with Nuendo 4.2.2 recording the QM12i and the ST350.

Right: the Cantar-X recording the Double MS assembly.

 
Highslide JSThe wiring behind the audio interfaces.   The wiring behind the audio interfaces:
  • 4 mic-levels from the QM12i into the two ULN-2
  • 4 line-levels from the ST350 control unit into the Fireface 400
  • Wordclock going from the bottom ULN-2 to the second ULN-2 to the Fireface 400
  • FireWire going from one unit to the other into the MacBook Pro
  • SPDIF out of the bottom ULN-2 to a Benchmark DAC1 (not shown)
 

Warm thanks to Yves-G. Préfontaine for letting us record his recital.

Photos by the workshop's participants.

 
 

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