Category: Voyage Audio

The Spatial Mic Converter plugin transforms the raw audio signals from Spatial Mic to a format useful for audio production.The output from Spatial Mic Converter can decode to first or second order ambisonics in ambiX or FuMa formats, in addition to mono/stereo virtual microphone patterns with flexible higher-order options. To accomplish this, Spatial Mic Converter uses an internal 64-channel filter matrix and measurements from an anechoic chamber. Spatial Mic Converter is available as VST3 and AAX and requires a host that supports multi-channel audio tracks such as Reaper, Pro Tools Ultimate, Nuendo or Plogue Bidule. The plugin and demo session are available as free downloads to test system compatibility.

Link: Download Spatial Mic Converter & free listening session

Spatial Mic Converter offers the capability to change the microphone’s aim at the point in space where the audio was recorded. This is useful when aligning audio position with 360 video, aiming the mic at specific sounds that should be in front of the listener, or used in combination with the virtual mic output stage to focus directional polar patterns at different parts of the soundfield.

Link: Skip ahead to learn about the virtual mic output and pattern decoding with Spatial Mic

The ambisonic output can be sent to a variety of plugins from Facebook 360, SSA, Blue Ripple Sound, IEM, SPARTA and others for further processing while mono or stereo outputs can be used with standard mono/stereo audio production plugins.

Usage

The built-in Spatial Mic Converter filters are specific to the raw signals from Spatial Mic and as such are only valid for Spatial Mic. Note that the plugin also offers the ability to load custom 64-channel .wav filters for any 8-channel second order microphone, however this is beyond the scope of this article. Spatial Mic Converter should be the first plugin in your signal chain when processing the raw signals from Spatial Mic.

Controls & InterfaceControls

Filter

Four built-in filters that transform the raw capsule output are available. Type 1 and Type 2 allow for a tonal choice and both have complimentary low noise versions. In general, the Type 1 filter selection will have a slightly more pronounced mid-range vs Type 2. While Type 1 and Type 2 offer the best spatial resolution, Type 1 LN and Type 2 LN conversion filters offer lower noise alternatives for recording quiet sound sources.

Options: Type 1, Type 2, Type 1 LN, Type 2 LN, Custom (64-channel .wav expected)

Tilt

Tilts the Spatial Mic recording direction up and down. Rotation and roll are maintained when tilting.

Range: ±45°

Default & Reset: 0°

Rotation

Rotates the Spatial Mic recording direction left and right. Tilt and roll are maintained when rotating.

Range: ±180°, continuous

Default & Reset: 0°

Roll

Rolls the Spatial Mic recording direction side to side. Tilt and rotation are maintained when rolling.

Range: ±45°

Default & Reset: 0°

Highpass

Activates a selectable frequency high pass filter, useful to cut wind noise or other low frequency artifacts.

Options: Off, 80Hz, 120Hz, 150Hz

Orientation

It is often desirable for the orientation to correspond with the real-life position of the microphone.

Normal: The Spatial Mic capsule array is aimed up.

End-Fire: The Spatial Mic capsule array is aimed forward.

Inverted: The Spatial Mic capsule array is aimed down.

Trim

Controls input level. Plugin processing may increase the signal level. If output meters clip, you may need to reduce trim.

Range: -20dB to +20dB

Default & Reset: 0dB

Outputs

Selects the output type. This should correspond to the input type of the next plugin in the signal chain. Note that the output types differ in channel count, ordering and level weighting.

Options: ambiX 2nd Order, ambiX 1st Order, FuMa 2nd Order, FuMa 1st Order, Virtual Mic

R Channel Output Note: The ‘R’ channel is silenced by default unless the Tilt control is adjusted. By clicking on the ‘R’ channel label of the output meter, Spatial Mic Converter plugin will generate the R channel from the W channel. When enabled the R icon will change to a green color. This may enhance the presence of height to recordings that are mostly horizontal, however it is best to use your ears to confirm this is the right choice.

Interface

There are 3 main sections to the Graphical User Interface.

Processing

This section displays and allows user input to change mic orientation, rotation, filter and more.

Inputs

Shows the unprocessed level with clip indication for each of the 8 capsules.

Outputs

Shows the processed output level with clip indication. Channel ordering changes based on output format selection.

Virtual Mic Output

The Virtual Mic output section enables the creation of  mono or stereo microphone polar patterns that can be aimed in the soundfield using the plugin tilt, rotation and roll controls. The virtual mic interface is shown on the plugin GUI when it is selected under the Outputs dropdown menu as shown below.

Polar patterns are created using three controls:

Type

Four different types of virtual mic decoding are available: In-Phase, Basic, max rE and Figure 8. Within each type, the pattern and width can be adjusted to manipulate the stereo field and polar pattern shape.

Figure 8: Traditional Omni → Cardioid → Figure 8 microphone patterns

Basic: Virtual mic patterns capable of second order cardioid (pattern = 2)

Max rE: Maximizes energy concentration vector by focusing energy signals in the direction of interest.

In-Phase: Full side-lobe suppression with no out-of-phase components

Pattern

The pattern control is continuously adjustable and changes the focus of the pattern from omnidirectional to a narrow pattern based on the virtual mic type selected. The pattern control can also be thought of as changing the ‘order’ from 0→1 for Figure-8 and 0 → 2 for all other pattern types. 

Width

The width control duplicates the polar pattern created and offsets their aim by the selected angle to create a virtual stereo microphone pair. The stereo width angle is continuously variable from 0° → 180°. When Width = 0, a mono signal is created.

Presets

Spatial Mic Converter has 15 built-in presets to quickly audition different configurations. The following chart shows the characteristics of each one.

Going Further

We hope you enjoyed this walk-through of the Spatial Mic Converter plugin. The ability to decode second order ambisonics as well as virtual mic patterns opens up a wide array of possibilities. In the future, we’ll look at using multiple plugin instances and the virtual mic to decode channel based formats such as 5.1 and 7.1 in addition to a highly configurable Mid-Side decoder. Drop us a line and let us know your favorite configuration or further enhancements that you’d like to see to this powerful tool!

With the ability to aim virtual microphones and craft an immersive 360 VR experience, Spatial Mic lends the possibility for great flexibility. In this article we will explore a live concert recording created with Spatial Mic.

Take a listen to Dreamers’ Circus performing ‘Prelude to the Sun’ — a nordic folk remix of Bach’s Violin Partita No. 3 in E Major. This live concert recording was captured with a single Voyage Audio Spatial Mic at the Conrad Prebys Performing Arts Center in La Jolla California.

The 8 channels of audio from Spatial Mic have been decoded to coincident supercardioid microphone patterns at a 90 degree angle for this recording. Later in this article we will learn how to change the pattern. To experiment and listen to the recording in its un-mastered, raw state, first download either the Pro Tools (Ultimate is required) or Reaper DAW session below, along with Spatial Mic Converter plugin (AAX and VST3). The audio in these sessions is uncompressed 24-bit / 96 kHz, so may take some time to download.

• Download Reaper Session 
• Download Pro Tools Session 
• Download Spatial Mic Converter Plugin 

The Setup

As we discussed in a previous article, techniques for capturing live concerts can vary wildly depending on the genre of music, concert space, gear available and experience of the recording engineer. With limited microphones, there is a trade-off between direct sound from instruments and diffuse reverberant sound from the room. The distance at which the diffuse sound and direct sound are equivalent is sometimes referred to as the ‘critical distance’ or ‘diffuse field distance’. When recording an ensemble with Spatial Mic, it is important to understand how the mic will react at different distances from the performers and position the mic accordingly.

As you can hear, the mic was positioned by audio engineer Matt Birchmeier in such a way that the final outcome produced a pleasant balance between the direct sound from the performers and the diffuse field of the room in which it was captured. The location of Spatial Mic can be seen right in the middle of the picture below, in front of Dreamer’s Circus and as you listen, see if you can hear the violin player move in the soundfield as the musician moves on stage.

Spatial Mic can be connected to a laptop via a USB to Ethernet extender, which can allow for 200ft of separation. Using this method, the analog mic gain can be controlled remotely from the laptop using the Spatial Mic Control app, while 8 channels of audio is recorded directly into Reaper at 24-bit / 96kHz.

Exploring The Recording

Once you’ve downloaded the session above, you can experiment with decoding the recording to different formats. Go ahead and open the session. In this case we are looking at the Reaper session as shown below:

As you can see in the Spatial Mic Converter plugin window, the default decode is the same Supercardioid Virtual Microphone pair used for the SoundCloud clip. The Stereo audio from the SoundCloud clip has been mastered after rendering this stereo audio.

There are many presets available to listen in different virtual mic configurations. Go ahead and use the preset drop down menu and select from different options. Here is the location of the presets in Reaper:

The presets available are as follows:

Using these presets as a starting point, go further and see how changing the virtual mic parameters ‘Type’, ‘Pattern’ and ‘Width’ change the sound. Use the Rotation, Tilt and Roll to aim these patterns in different directions.

If you’d like to dive deeper into the controls and also learn more about In-Phase, Basic, max rE and Figure 8 patterns, check out this article on the Spatial Mic Converter plugin.

Ambisonics, ATMOS & Surround 

With the original recording you can decode to any format you wish. Let’s take a look at some common formats and how to decode.

Ambisonics

The Spatial Mic Converter plugin can output 1st (4 channels) and 2nd (9 channels) order ambisonics in FuMa and ambiX weightings. Most modern plugins use ambiX, especially for higher orders, however there are plugins like the Ambisonic Toolkit that use FuMa weighting.

Simply setup the output section to match the next plugin in the chain. For example, to decode ambisonics to stereo binaural, place a binaural converter directly after Spatial Mic Converter. 

Here are some plugin bundles that contain binaural decoders:

• IEM BinauralDecoder (Up to 7th order ambiX ; VST)
• SSA Monitor (Up to 7th order ambiX; VST & AAX)
• FB360 (Up to 3rd order ambiX ; VST & AAX)
• Waves Nx (1st order ambiX ; VST & AAX)
• ATK Binaural Decoder  (1st order FuMa ; JSFX for Reaper )

Here is Spatial Mic Converter and SSA Monitor setup for binaural decode:

Ambisonics can also be decoded to different speaker arrays and setups using decoders from various plugin manufacturers.

ATMOS

In a previous journal article we learned how Lenny Jones (Ancient Aliens, Curse Of Oak Island, Unsolved Mysteries) delivers sound effects in Atmos 7.1.2. Let’s take a closer look at the various ways in which this can be done.

To decode from Spatial Mic Converter 2nd order ambisonics output to Atmos 7.1.2  there are different approaches you can take. They all require a DAW plugin to be inserted between the Spatial Mic Converter plugin and the Dolby Atmos Production Suite plugin. Keep in mind that Atmos Production Suite requires Pro Tools Ultimate and only works on OSX.

Here are a few options to convert from Spatial Mic Converter Plugin to Dolby Atmos:

1. Blue Ripple Sound ATMOS decoder. This plugin is Pro Tools compatible and accepts up to 3rd order ambisonics, so put the 9 channels from Spatial Mic Converter plugin into the first 9 slots and then leave 10-16 silenced.    
2. Harpex. Another Pro Tools compatible plugin. Route the  first 4 channels from Spatial Mic converter plugin output into the plugin. Even though only 1st order ambisonics is used, the spatial resolution will be higher from the 8 capsule Spatial Mic array than other 4 capsule 1st order microphones.
3. Use the Sparta Compass Decoder or IEM ALLRAD Decoder, both of which are free but not available as AAX for Pro Tools. Using one of these plugins, render 7.1.2 in a separate DAW like Reaper and then bring the resulting files  into Pro Tools Ultimate for conversion with the Dolby Atmos Production Suite.

Surround

If you’d like to listen on 5.1, 7.1 or other channel based surround formats you can use some of the same tools we looked at for Atmos like Harpex and the Blue Ripple Sound decoders. Blue Ripple Sound also has a free 03A Core plugin suite that includes a 5.1 Basic decoder. The difference is that you will not need to use the Dolby Atmos Production Suite, but rather use the output from these plugins as your speaker feeds.

A quick way to audition channel based formats is to use the Sparta ambiDec or compass_decoder plugins. These are both free VSTs included in the Sparta plugin installer. The Sparta website describes ambiDec is a “A frequency-dependent loudspeaker ambisonic decoder (up to 7th order) with user specifiable loudspeaker directions (up to 64)” while the compass_decoder uses a parametric approach up to 3rd order. Here is a setup with ambiDec showing the various decode presets available:

Going Further

As you can see there are many approaches to decoding. Beyond the methods we covered in this article, other third party tools like SPAT Revolution from Flux include options for advanced panning techniques and loudspeaker configurations.

Do you have a favorite method to decode spatial audio? What method or virtual mic pattern sounds best to you?  Let us know

Finally, a big thanks to Dreamers’ Circus ( http://www.dreamerscircus.com) for letting us use this recording and to Matt Birchmeier (http://www.mattdbirchmeier.com) for making this happen.