Using the AMBEO Ambisonics Mic with the MixPre 6 and Pro Tools Templates
About Ambisonics
An ambisonic recording uses a multi-capsule microphone to capture a spherical representation of sound from a single point. It is a very good way to record spatial environments and ambiance.
It can be decoded many different ways after recording: Stereo, quad, 5.1, and 7.1.2. It also works well with Dolby Atmos. Complex rebalancing can be done with a plugin in Pro Tools.
Ambisonic recordings are captured in A-Format or B-Format.
A-Format is the raw audio captured from each capsule on the microphone.
This is what we will record with the MixPre 6.
B-Format is the decoded audio, representing the spherical sound space with 4-channels, W, X, Y, Z.
We will convert out the A-Format file to B-Format in Pro Tools using Plugins.
B-Format comes in two versions, with different orderings of the formatted channels: FuMa & AmbiX. There is no difference in the audio itself.
AmbiX is more popular so we will use it in Pro Tools.
Part 1: Recording Ambisonics with the MixPre 6
—Setting Up:
It is very important that all four channels be recorded at exactly the same level, The MixPre 6 has a special plugin already installed to properly record Ambisonics. However, you will also need to install a preset to record the Sennheiser AMBEO properly.
This is the same process as with the other MixPre presets. To review downloading and installing presets, please read the Loading MixPre-3 and MixPre-6 Presets article. The special preset you need to download is called AMBEO_MP6_A-Fmt_1-24.
Click here for a direct link to download the AMBEO preset.
After you’ve installed the preset, hook up the mic
- Yellow XLR 1 to MixPre XLR input 1
- Red XLR 2 to MixPre XLR input 2
- Blue XLR 3 to MixPre XLR input 3
- Green XLR 4 to MixPre XLR input 4
The AMBEO mic can record in three different positions. It’s important the mic position matches the MixPre setting so that the sound can be properly decoded later.
The mic is usually used vertically (“up”,) and that is the default setting. The word “front” should face forward.
If you need to change the mic position, you can go to Inputs > Ambisonics > Mic Position, and set the correct Mic Position to match the physical orientation of the mic.
—Recording:
Notice that only the first volume control knob does anything. It’s very important that the gain be exactly the same for all four channels, so they are all controlled by the same knob.
The metering is somewhat different too:
(Tap the Home screen if you don’t see these meters.)
The meters are now vertical. On the right, “bl” and br” are a binaural downmix which is going to the headphones. It gives an approximation of the 3-D sound field. It is not normally recorded.
Now you can start recording!
Your files will have four channels, and their names will end in “_A_FMT.WAV”
Part 2: Using Ambisonic Files in Pro Tools
Now we will bring out files into Pro Tools. Ambisonics has not been part of our normal workflow, so we will need to modify a template track, and then use two plugins to decode and premix the Ambisonic recordings.
—Importing the Files Into Pro Tools:
We can use any audio track to decode these files, but since it is surround sound, it makes the most sense to use the Mix or Atmos templates. For this example, we will use the mix template, and put our files on a background track, since ambience is the most common use of Ambisonics.
We will use the first stereo track. Double-click to change its name to something we will recognize.
After the change is made, right-click on the track’s name, select Change Track Width > 1st Order Ambisonics.
Click OK to change the panning setup.
Now we have a four-channel track, as we can see by its meters.
Now we can import our files and put them on the track.
The audio should play now. But it’s not decoded yet!
—Decoding and arranging the Ambisonic audio:
We will need to add two plugins to the track to properly decode out audio.
First drag the Channel Strip plugin down to the third insert position on the list so the decoding can happen before the eq & dynamics.
Now, in the first insert position, add the AMBEO A-B Format Converter.
The AMBEO A-B Format Converter does two things: It compensates for eq quirks in the microphone itself, and it converts A-Format to B-Format. You don’t need to adjust anything on this plugin, unless you recorded using a non-standard mic position.
In the second insert position, addthe SoundField by RODE plugin.
—If you are in the Mix template, use the 1st Order Ambisonics/5.1 iteration.
—If you are in the Atmos template, use the 1st Order Ambisonics/7.1.2 iteration.
Click OK to change panning setup.
Very Important! You MUST change the input setting to B-Format (AmbiX)
Here is the 5.1 iteration. It is where all the magic is done. It creates a 5.1 sound field, and gives us control of our “virtual microphones”.
Adjustments should be done when listening on a proper surround system.
The upper-right controls change output volume levels.
The lower-left buttons change “microphone” type — directional or omni.
The lower-left circular faders change how directional the “microphones” are — either collectively, or individually if you disable the “chain” button.
The sound field can be rotated, and individual mics can be rotated or tilted up and down in the two large circles.
When playing back audio, colors will appear showing position and amplitude of the original sound. This can guide you in adjusting your “virtual microphone” positions.
Here’s the original sound playing back:
And here’s an adjustment to make it more centered:
And another adjustment to widen the sound field.
Finally, here’s the 7.1.2 output of the same recording being sent to a Dolby Atmos bed:
Recording with the AMBEO mic can create very immersive sound environments. Although the setup requires more steps than conventional mono or stereo recordings, it’s not hard to do. And when you find mixes that you like, you can bounce them out of Pro Tools and save them for later use without the plugins.
Enjoy!