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Core Sound TetraMic -- Recording With TetraMic
TetraMic Recording Tips

(Last updated 11/06/2016)

Typical Recording Set-ups

TetraMic 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 the compact shock mount we supply with TetraMic or another one of your choice that is at least as effective.

TetraMic's output is a 6-pin mini-XLR jack. A 6-pin PPAc adapter cable plugs into TetraMic and connects to the PPAc transmitter. Since TetraMic's signal is unbalanced at that point and somewhat susceptible to picking up strong electrical interference, we recommend keeping that adapter cable length as short as possible and routing it away from sources of interference.

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

Using TetraMic with a Portable Digital Audio Recorders

Tascam's DR-680MkII eight channel portable digital audio recorder is probably the most cost-effective and simplest way to record with TetraMic. The combination makes very high quality ambisonic recordings. You can buy a DR-680MkII in the US for $600 or less.

Alternatives to the DR-680MkII are the Tascam DR-701D, Zoom F8 or F4, and Sound Devices MixPre-6. Of the three recorders, the DR-701D is the smallest. The F8 has the most mic pre-amps: eight.

Connect TetraMic to the recorders using our PPAc system. The PPAc receiver's XLR connectors plug directly into four of the recorders' XLR inputs.

All of the recorders mentioned have very accurate, digitally-set level controls so it's very easy to match the levels across TetraMic's four channels. The DR-680MkII and the two Zoom recorders can even gang the four channels so that you can control the levels with one knob. All four recorders are recommended!

Using TetraMic with an iPad

The folks at n-Track report that their n-Track Studio 7 application runs great on the iPad. You can record pristine 192 khz/24-bit multichannel audio without having to carry around a heavy computer and with the ease of use typical of the iPad.

The iPad is compatible with USB devices that support Class Compliant USB Audio. Those are typically the devices that work when you connect them to a computer without having to install any driver software.

Check with them for recommendations about audio interfaces that work well with Studio 7 and the iPad.

Using TetraMic with a recorder that doesn't have digitally-set levels

Connect TetraMic to the recorder's four XLR inputs using TetraMic's PPAc system.

If the recorder does not have level controls that are set digitally, you would first set each channel's Sensitivity and Level controls, lock them down so that they can't change, and then record a stable tone to each of the four channels. Low-cost tone generators are available from Behringer (the CT-100), Shure (the A15-TG) and other audio manufacturers.

In post-recording (back in the studio), adjust the levels of the four recordings of the tone so that they are within a tenth of a dB of each other. Note the adjustments in gain for each channel, and apply them to your recordings.

Using TetraMic With a MOTU Traveler or 4Pre

If you're using a MOTU Traveler or 4Pre mic pre-amp, plug the TetraMic's PPAc receiver cables into the Traveler's or 4Pre's inputs.

The MOTU Traveler can be used with PC, via a FireWire (IEEE-1394) interface, or as a stand-alone front end with four channel recorders that have Line inputs and excellent gain tracking between channels. The 4Pre can use FireWire or USB.

When used with a PC, you can use any of the many digital audio workstation software applications. Here at Core Sound we use Ross Bencina's AudioMulch. One requirement for the DAW software is that it has identical latencies for all four channels to preserve sample sync. ASIO drivers seem to do this well, and the MOTU Traveler is provided with ASIO drivers.

One stand-alone digital recorder that folks have used with great success is the Sound Devices 744. While it only has two microphone pre-amps (two short of TetraMic's four outputs), the MOTU Traveler's (or 4Pre's) four mic pre Line outputs can be plugged into the 744's Line inputs. The 744 has the ability to set the gains on its Line inputs digitally, precisely preserving gain matching across channels.

Recording with TetraMic, MOTU Traveler (or 4Pre) and a PC

We recommend recording using 24-bit word widths, at a minimum of 44.1 KS/s sample rate. Set gains for all channels to the same setting. If you're recording large choirs or orchestras, a good start is 15 dB. Try to get peaks at around -15 to -20 dB. If you're recording loud rock concerts, set levels to 0 dB; note that to keep from overloading the mic pre-amps you might have to also use the Traveler's (or 4Pre's) 20 dB pads (attenuators).

If you are using a DAW that can use VST plugins, you'll be able to monitor the recording in real-time, fully decoded, and record either A-format (four channels), B-format (also four channels) or files decoded to any specific microphone and playback configuration (from 1 to a very large number of channels). The VVTetraVST plugin does the calibration corrections and the A- to B-format conversions. The VVMicVST plugin does the decoding to set microphone parameters (e.g., number of microphones, the angles at which they point, each one's directivity) and match your playback system configuration.

If your DAW doesn't use VST plugins, then you'll record four channels of A-format and do post-processing later. Post-processing consists of applying the calibration functions for your specific TetraMic, and selecting microphone and playback configurations. The post-processor you'll use will be "TetraMic for VVMic", a Windows application that we supply with TetraMic at no extra charge. See the section on Post-Processing below.

Alternately, if your PC runs Linux, you can use Fons Adriaenson's TetraProc software using calibration files that Fons will provide for you. Fons creates the calibration files using the same test data we use here Core Sound to create the calibration data used with "VVMic for TetraMic". Contact us for details.

Recording With TetraMic, a MOTU Traveler (or 4Pre) and a Sound Devices 744

If you're recording with a standalone digital audio recorder, make sure that the gains on all channels are set identically. What you'll be recording is the raw TetraMic output, called "A-format".



For pre-sales consulting or to place an order, call Core Sound at 1.888.538.6744 or 1.201.801.0812.

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