(Last updated 08/10/2009)
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 35 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 jack is a 6-pin mini-XLR. To allow you to mount
TetraMic on a stand and get the signal down to your recorder, use a
6-pin extension cable (6-, 10- or 20-foot). Since TetraMic's signal is
unbalanced at that point and somewhat susceptible to picking up strong
electrical interference, we recommend keeping that cable run as short as
possible and routing it away from sources of interference.
The extension cable 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 PC or
a stand-alone digital audio recorder.
Using TetraMic with an Edirol R-44 Four Channel Portable Digital
Audio Recorder
Edirol's R-44
four channel portable digital audio recorder works fine with TetraMic
and is a very cost-effective way to make high quality ambisonic
recordings. You can buy an R-44 in the US for around $900.
Connect TetraMic to the R-44 using an extension cable, breakout cable
and four Phantom Power Adapters (PPAs). We recommend keeping the
extension cable as short as possible.
The R-44 does not have level controls that are set digitally, so to
match the levels across the four channels 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.
For sound sources of moderate loudness, a good starting place for the
R-44's sensitivity controls are -38 dB. That seems to improve the
R-44's not-quite-stellar harmonic distortion specifications.
Using TetraMic With Core Sound's 4Mic
If you're recording with one of our 4Mic multiplexing four-channel
mic pre-amp/ADCs, at the other end of the extension cable you'd connect
a 4Mic breakout cable. The breakout cable has a 6-pin mini-XLR jack on
one end (to plug into the extension cable) and two 5-pin mini-XLR jacks
that plug into 4Mic's mic inputs.
[Under construction]
Using TetraMic With a MOTU Traveler
If you're using a MOTU Traveler mic pre-amp, you'll need four Phantom
Power Adapters (PPAs) and a TetraMic breakout cable. The breakout cable
has a 6-pin mini-XLR jack on one end (to plug into the extension cable)
and four 3-pin mini-XLR jacks on the other that plug into the four
PPAs.
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.
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 Device 744. While it only has two microphone
pre-amps (two short of TetraMic's four outputs), the MOTU Traveler'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 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 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 configuration. 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.
[Under construction]
Recording With TetraMic, a MOTU Traveler 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".
[Under construction]
Recording With TetraMic, 4Mic and a Two-Channel Recorder
[Under construction]
Post-Processing
[Under construction]
What is "A-Format"? What is "B-Format"?
[Under construction]
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