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.

Downloads

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.

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

The Metric Halo and RME audio interfaces are connected to an Apple MacBook Pro 2.4 GHz running macOS 10.5.5 and Steinberg Nuendo 4.2.2 DAW. The audio interfaces share the same wordclock and are grouped with the Mac macOS Aggregate Audio Device feature to present only one audio interface to the recording software. The recording is done at 24 bit and 48 kHz.

The Double MS will be recorded on a Aaton Cantar-X.

Line Audio QM12i microphone courtesy of Etienne Bovo.

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

Right: second stand with Double MS assembly.

Right: recording and monitoring the Double MS assembly.

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

• 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 participants.