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Core Sound OctoMic™ -- Recording With OctoMic
OctoMic Recording Tips

(Last updated 04/03/2020)

Recording With OctoMic

Typical Recording Set-ups

OctoMic has an unusually extended low frequency response. If we wanted to go a bit overboard, we could calibrate it to be flat to well below 20 Hz and you could use it as an earthquake detector! But we reasonably limit its response so that it's usable down to around 25 Hz.

As with any high quality microphone that works well down to those very low frequencies, you must use a shock mount unless you really want to pick up footsteps, trucks rumbling by, distant thunder and subway trains. So please always use an effective shock mount. (See the OctoMic Accessories page for recommendations.)

OctoMic's output is a 12-pin jack. A 12-pin PPAc8 cable connects it to the PPAc8 transmitter. Since OctoMic's signal is unbalanced at that point and somewhat susceptible to picking up strong electrical interference, we recommend keeping that PPAc8 cable length as short as possible and routing it away from high power sources of interference.

The PPAc8 transmitter connects to two shielded EtherCon cables, each of which carries four channels. The EtherCon cables can run for more than 500 feet without degrading the audio signal.

The two EtherCon cables connect to two PPAc8 receivers. Each receiver has four XLR plug outputs, for a total of eight.

OctoMic's PPAc8 system can feed the signal to either an eight-channel recorder that has its own mic pre-amps, or an eight-channel microphone pre-amplifier/ADC (analog-to-digital converter) that feeds an eight-channel digital audio recorder. The recorder can be either a computer or a stand-alone digital audio recorder.

Using OctoMic with Portable Digital Audio Recorders

Zoom's F8 and F8n eight-channel portable digital audio recorder are probably the most cost-effective and simplest ways to record with OctoMic. The combination makes very high quality 2nd-order ambisonic recordings. You can buy a Zoom F8 or F8n in the US for $1000 or less.

An alternative to the Zoom F8n is the Sound Devices MixPre-10 II.

Other possible alternatives are the Sound Devices 788T, Roland R-88 and the SonoSax SX-R4+/SX-AD8+ combination.

Connect OctoMic to the recorders using OctoMic's PPAc8 system. The PPAc8's two receivers terminate in eight XLR connectors. Plug them directly into the recorders' eight XLR inputs.

Both the Zoom F8n and the Sound Devices MixPre-10 II have very accurate, digitally-set level controls so it's very easy to match the levels across OctoMic's eight channels. Both recorders can gang the eight channels' level controls, so you can control the levels with one knob. Both recorders are recommended!

Microphone Pre-amplifiers and ADCs

To preserve OctoMic's calibrated performance, all eight OctoMic channels should be gain-matched to within 0.1 dB. Please use mic pre-amps and A-to-D converters that are designed to hold those gain tolerances across eight channels.

DAWs for Editing OctoMic Recordings

OctoMic's raw eight-channel audio output are in what's called "A-format". When you transfer them into your digital audio workstation for editing, convert them to standard 9-channel 2nd-order B-format with the supplied VVOctoEncoder VST encoder plugin.

The following DAWs can be used for editing 2nd-order B-format:

  • Reaper
  • Pro Tools HD
  • Cubase (pending)
  • Nuendo (pending)
  • Pyramix (v11.1 and higher)
  • Ardour
  • Digital Performer
  • Plogue Bidule
  • AudioMulch
  • FLStudio (with proper mixer and plugin I/O configuration)

If your PC runs Linux, you can use Fons Adriaenson's OctoProc software.

OctoMic's 9-channel B-format has been confirmed to work well with the Facebook 360 Spatial Workstation.

VVOctoEncode VST/AAX Encoder and Plugin Options

VVOctoEncode is the A-to-B-Format encoder VST/AAX plugin supplied with OctoMic. It was developed and is supported by David McGriffy (VVAudio.com).

Once you have your coupon code from us, you can download VVOctoEncode here.

VVOctoEncode allows you to select among three options during encoding.

The first option has the least processing noise and provides excellent spatial location cues.

The second option adds a slight amount of processing noise but has slightly stronger spatial location cues.

The third option adds a bit more processing noise but has even slightly stronger spatial location cues.

We advise that when encoding very quiet sound sources, that Option 1 be the default selection. When the sound sources are louder, we advise considering using Options 2 or 3.

Octofile A- to B-format Encoder for Linux

We have great news for OctoMic users who work in Linux environments!

Fons Adriaensen has released the source code for Octofile version 0.3.0.

Octofile is an A- to B-format encoder for Octomic.

Using OctoMic As A Blumlein Array

OctoMic is the world's finest Blumlein array. See the X and Y B-format channel polar patterns to confirm this.

To use OctoMic as a Blumlein array:

  • Place the OctoMic where you judge the sound is good.
  • Record.
  • Encode the A-format recording to B-format with VVOctoEncode (the encoder plug-in supplied with OctoMic).

    Channels 2 and 4 of the 9-channel B-format output are channels X and Y. They are the two orthogonal (crossed) figure-8 microphones. Use Channel 2 as right, and channel 4 as left.

  • If during recording you had the OctoMic facing forward, rotate the array 45 degrees with any reliable rotation plugin. (We use SSA's a3Rotate plugin.)
  • Record the new stereo track
  • You're finished!

If you use a block and wire application like Plogue Bidule for your plug-ins, here's what the layout looks like:

It takes second-order B-format as input, and both plays and records Blumlein.

Using OctoMics In Spaced Arrays

Some recording engineers prefer recording with spaced arrays of microphones to coincident arrays. Recordings made with spaced arrays offer a sense of spaciousness due their spatially decorrelated ambiences.

The simplest spaced array is probably the ORTF array. Two first-order cardioid microphones are spaced 17cm apart and aimed at +/- 55 degrees (110 degrees between them).

Two OctoMics make a superlative ORTF array. That's because their decoded first-order cardioid directivity patterns are almost perfect up to around 10 kHz. (See OctoMic's polar directivity patterns here.)

And since the first-order cardioid mic decodes used in this ORTF array are decoded in post-production, the aiming of the two cardioids can be easily fine-tuned back in the studio.

This same approach can be taken with larger and more complex spaced arrays, including ESMA, ESMA-3D, ORTF Surround and ORTF-3D, Hamasaki Square and Cube, Decca Tree and many others. They all benefit from OctoMic's very precise and stable first-order decodes.

There's another benefit to using OctoMics in spaced arrays: lower cost. For example, in an ORTF-3D array, there are two first-order supercardioid microphones at each corner of the array. If you were using mono mics, you'd need two physical microphones at each corner, for a total of eight mono microphones. In contrast, you can populate that array with only four OctoMics. Each OctoMic gets decoded to two virtual microphones.

For a nice surprise, compare the cost of the eight high-end mono microphones in an ORTF-3D array to the cost of four OctoMics!

ORTF Array With Two OctoMics

ORTF-3D Array With Four OctoMics

Here's how we did the ORTF decode using Plogue Bidule:

We recorded A-format (raw capsule audio from the two OctoMics) to a sixteen track recorder. Tracks 1 through 8 were from the left OctoMic. Tracks 9 through 16 were from the right OctoMic. Each OctoMic's A-format were encoded to B-format using one VVOctoEncode plugin (supplied with each OctoMic) using its own specific calibration files. The B-format outputs went to two instances of SPARTA Beamformer. Both were set to decode to first-order cardioid. The left Beamformer was rotated to -55 degrees, and the right to +55 degrees. The outputs of the two Beamformers went to a gain control and then to a player and file recorder.

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