Recording techniques using the Austrian Audio OC818’s Dual-Output design
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Recording techniques using the Austrian Audio OC818’s Dual-Output design

OC818 is a dual large diaphragm, multi-pattern condenser microphone with a switchable high-pass filter and two pad settings for attenuating the signal before the electronics and/or the output gain. At the heart of OC818 is a brand new capsule designed by Austrian Audio but based upon decades of Viennese capsule experience. The CKR12 (Capsule Keramick Ring) is an edge terminated capsule that is made by hand, one-at-a-time by a lady , “Monika”, an industry legend in Vienna who has been making mic capsules for over 30 years.

One of OC818’s standout features is its mini-XLR output on the rear of the mic body. This output is a discrete output of the second ‘rear-facing’ diaphragm and allows the engineer and artist to record both front and rear diaphragms separately and processes them individually in their DAW of choice.

This lends itself to a few different useful applications:

  • Recording two musicians simultaneously, e.g. a singer facing one diaphragm, a guitarist using the other.
  • Recording a two part choir, e.g. one part positioned around one diaphragm and the other part positioned around the other.
  • Capturing both direct and ambient signals of the same instrument, e.g. recording a drum overhead signal with the diaphragm facing the kit and blend in the rear-facing ‘room ambience’ signal captured by the rear capsule.
  • Recording in stereo, e.g. rotate the mic 90° and use one capsule to record the left signal, and the other capsule to record the right.

The advantage of using one mic for these applications rather than two separate mics is that due to the proximity of both diaphragms, the two signals being recorded remain in phase with one another with minimal risk of comb filtering occuring.

Comb filtering occurs when the same audio signal reaches two separate microphones at slightly different times. When these mic signals are then summed together in the mix, even a small delay between the two microphones can cause destructive notch filters that cut frequencies in regular intervals and result in a hollow and ‘out-of-phase’ sound. As OC818’s diaphragms are part of the same CKR12 capsule and live fractions of millimetres apart, the comb filtering is minimal and the stereo signals recorded are phase coherent.

To put the OC818 to the test, I grabbed an acoustic guitar and aimed to make the most out of the dual-outputs for two of the above use cases.

Recording Signal Path

For the recording chain, I sent both diaphragms of OC818 into a matched pair of Camden 500 preamps from Cranborne Audio - if you don’t know about these preamps, they are one of the cleanest, most transparent preamps on the market and they’re perfect for testing out a mic! https://www.soundtech.co.uk/musicians-blog/our-guide-to-the-camden-500

I then sent the preamp outputs into an Apogee Symphony MKII - which is widely considered one of the most accurate and detailed converters on the market. This signal chain was designed to record every subtle nuance of OC818!


Recording Direct And Ambient Signals

For the first example, I setup the OC818 to face the acoustic guitar directly by the 15th fret of the guitar. I planned for the front diaphragm to capture the direct guitar signal whilst the rear diaphragm captured the room ambience. Both preamp gains were set to the same position and the OC818 was configured to output a cardioid pattern from each of its diagrams. In post-production, I sent both mic signals into a bus and processed them with a tiny amount of compression (to help get the levels up to YouTube standards!).

During the video, you can hear how the rear facing capsule can help add a little bit of depth to the recording and put the guitar ‘into-the-space’ of the studio - whilst it can sound subtle, it can become very obvious once the room signal is muted; 0:22 as the tone suddenly becomes one-dimensional and dry in comparison.


Recording In Stereo

Rotating the OC818 90° allows its dual-diaphragm design to record stereo sources with ease. Thanks to OC818’s incredible off-axis frequency response, even signals positioned at this angle to the diaphragms are picked up with the same fidelity as signals facing head-on. I positioned the mic around 6 inches from the 15th fret of the guitar and left the preamps and converters untouched.

In post-production, I panned the signals hard left and hard right to get the maximum possible width out of a single source. In the video you can clearly hear how wide yet natural the OC818 captured the acoustic guitar whilst retaining a solid centre image that is robust. This guitar sound was thick enough to stand by itself in the recording, but it could also be sat into a dense mix. You can hear how subtly the room reacts in each direction when they are solo’d at 1:06.


PolarPilot and PolarDesigner

The second output of the dual-diaphragm CKR12 capsule is not only to facilitate some imaginative recording techniques, it’s also designed to connect with OC818’s party piece, the OCR8 Bluetooth remote.

Connect OC818 to the OCR8 and now you have real time control of OC818’s polar pattern, HPF, and pad settings remotely using Austrian Audio’s PolarPilot app; available on Android and iOS. The app also displays a histogram of the audio passed through OC818 so that the engineer can track down any rouge peaks and clips and adjust the gain accordingly.

Taking this one step further, if you record both of OC818’s diaphragms in dual-cardioid mode into your DAW, you can use Austrian Audio’s free PolarDesigner plug-in to create your own completely custom polar patterns during the mixing phase of your project without committing to a polar pattern during the recording. Polar Designer allows you to scroll through global patterns such as Omni, Cardioid, Figure 8 as well as any combination in between. You can also assign different polar patterns to 5 separate frequency bands for even more unique effects; such as opening up the high-end with an Omni pattern whilst tightening the low-mid with a Hyper-Cardioid pattern. As it is a plug in, you can also automate those changes to a huge plethora of options for production. For example, you could set the drum overheads to a tight Cardioid pattern during the verses and then open up the pattern to Omni during the choruses for a fatter and more ambient drum sound.

To find out more, check out our dedicated blog posts for:

Polar Pilot 

Realtime app control of the OC818 via bluetooth

Polar Designer

Advanced polar response designer plugin 

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This new blog is presented by the team at Sound Technology Ltd, a leading distributor of musical instruments and pro audio equipment in the UK and ROI.